Experimental Archaeology: 1. Early Bronze Age Cremation Pyres; 2. Iron Age Grain Storage 9781407307862, 9781407322025

Table of contents :
Front Cover
Title Page
Copyright
CONTENTS
PAPER 1. Simulation of prehistoric cremation: experimental pyres, and their use for interpretation of archaeologicalstructures
Section 1: INTRODUCTION
Section 2: EXPERIMENT
Section 3: APPLICATION OF EXPERIMENTAL DATA
CONCLUSIONS
BIBLIOGRAPHY
CAPTIONS FOR FIGURES
CAPTIONS FOR PLATES
Figures
Plates
PAPER 2. Methods of grain storage during the Iron Age insouthern Britain: further investigation by experiment
Section 1: CONTEXT
Section 2: EXPERIMENTATION
Section 3: GENERAL DISCUSSION
CONCLUSIONS
BIBLIOGRAPHY
ACKNOWLEDGEMENTS
CAPTIONS FOR FIGURES
CAPTIONS FOR PLATES
Figures
Plates

Citation preview

BAR 530 2011  MARSHALL  EXPERIMENTAL ARCHAEOLOGY

Experimental Archaeology: 1. Early Bronze Age Cremation Pyres 2. Iron Age Grain Storage

Alistair Marshall

BAR British Series 530 9 781407 307862

B A R

2011

Experimental Archaeology: 1. Early Bronze Age Cremation Pyres 2. Iron Age Grain Storage

Alistair Marshall

BAR British Series 530 2011

ISBN 9781407307862 paperback ISBN 9781407322025 e-format DOI https://doi.org/10.30861/9781407307862 A catalogue record for this book is available from the British Library

BAR

PUBLISHING

CONTENTS Page 1

Preface

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Paper 1 Simulation of prehistoric cremation: experimental pyres, and their use for interpretation of archaeological structures.

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Paper 2 Methods of grain storage during the Iron Age in southern Britain: further investigation by experiment.

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experimental pyres

PAPER 1 Simulation of prehistoric cremation: experimental pyres, and their use for interpretation of archaeological structures. ABSTRACT Analysis of a series of fully-monitored experimental cremation pyres is used to supplement the interpretation of burnt pyre-bases, and other associated archaeological features, of the type found under Bronze Age round barrows in Britain, and to add detail to the process of ancient cremation. Keywords: cremation, pyres, experimental archaeology, round barrows, geophysical survey. further raised the question as to what additional invisible pyre- or fire-related trace-features might persist as magnetic enhancement in the archaeological record, of a type not defined by reddened, burnt sediment. In many cases the obviously baked original surfaces of such features may also have been removed by clearance of debris to leave only deeper magnetic enhancement. Weaker radiation from a pyre structure perhaps perched above the ground surface (PLATE 8b) might also have failed to redden sediment clearly.

Section 1: INTRODUCTION ARCHAEOLOGICAL BACKGROUND TO THE EXPERIMENTS Excavation in 1990-1992 of the round barrow at Guiting Power 3, located in the Gloucestershire Cotswolds at SP 09574 24660 (FIG 1), produced burnt surfaces, scatters of fire-debris, and deposits of cremated human bone in primary locations. All of these elements were critical for interpretation of the sequence of ritual at the site, and for discussion of its general function as a monument (Marshall 2007b). Guiting Power 3, in common with many barrows of its type, contained a primary cremated deposit in a central pit, dug into the ground surface before mounding for the barrow began, and which lay surrounded by burnt sediment and scatters of charcoal. The pattern of burnt material over this central area suggested that cremated remains were interred through a cleared pyre-base.

Viable and relevant data from experimental cremation, which might be directly used as a more objective basis for positive identification and more detailed structural analysis of such pyre sites, was also missing. Consequently, there was a general lack of information with which to define characteristic traces left by a prehistoric cremation pyre capable of cremating a human corpse, adult or child, single or multiple, to indicate more clearly pyre type, size, and intensity of combustion. Basic data were therefore required from a series of experimental simulations, which could provide standards for identification of these excavated structures, and against which variation in them could be gauged.

In seeking parallels for this central feature from Guiting Power 3, review of excavation at other similar barrows noted many comparable features and scatters elsewhere in southern Britain, variously interpreted as funerary deposits and possible pyre-bases. However, publication of such features almost entirely lacked data from geophysical analysis to quantify burning, and help define burnt areas by more objective means than visual.

Quantified experimental data were certainly required in order to re-examine, and more firmly identify, the possible pyre-structure already excavated at Guiting Power 3, and to review the partial evidence from other sites. Such advance information was also needed in planning excavation at a second, nearby round barrow, Guiting Power 1 (SP 08443 24461), where further evidence of cremation was expected, in order to take full advantage of integrating experimental data with excavated structure (Marshall 2007a).

After excavation, burnt areas from under round barrows were routinely plotted only in terms of clear visual changes seen in sediment, with differences between in situ burning and scattering or re-deposition of burnt material often left unclear. Pyre-, or fire-bases and burnt scatters, only of the most visually obvious type, were typically shown in outline. Possible pyre-bases were usually only identified by association with diagnostic central features, by cremated deposits interred through them, or by association with burnt timber structures, these latter being vaguely interpreted as 'mortuary structures' (FIG 15).

Three experimental cremations were, therefore, carried out in the Guiting Power area (around SP 0973 2470) during the intervening period between these two barrow excavations, for direct application to these particular projects, and to provide an opportunity to obtain more general information on the

This absence of magnetic data for visible structures

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experimental pyres question. The review does not attempt to present a complete summary of the archaeological evidence for structures and processes involved in cremation, even during the Bronze Age, and uses only selected relevant examples for comparative purposes. The main emphasis of this particular analysis is to match data from experimental pyres against excavated structures from the same area, with the same geological background, in this case oolitic limestone and derived clays. The methods used and conclusions drawn are of course applicable to other substrates, such as chalk or gravel, where many excavated interment-pyre sites occur.

process of ancient cremation and its impact on the archaeological record. Guiting Power 3 was excavated in 1990-1992, the first experimental pyre took place in 1993, the second in 1994, the third in 1995, and Guiting Power 1 was excavated in 1996 (Marshall 1998; 2007a). A series of further experiments has taken place since 1996, to examine the properties of other types of pyre, fired under a variety of conditions. Discussion is confined to pyre-bases of the type associated with cremated deposits in and under round barrows of the earlier Bronze Age, of the type common in southern Britain on the chalk and limestone (Ashbee 1960; Woodward 2000). However, the relevance of the analysis is more widespread since the type of pyre construction which generated these burnt features is fairly typical of those in general use amongst many prehistoric communities where routine disposal of the dead was by individual cremation.

Classification of pyres (TABLE 1; FIG 2) For the purposes of this analysis, two basic types of pyre-structure are distinguished: the 'box-pyre', comprising three sub-types, and the 'ring-pyre'. The box-pyre consists of box-shaped fuel-load stacked mainly horizontally, and has a basically rectilinear plan. The ring-pyre comprises a sub-conical fuel-load with increased vertical stacking, and has a basically circular ground-plan. Each type may include added timber structures, which can penetrate the ground or not, which would help retain the fuel-load, and could act to display the corpse prior to cremation.

The type of pyre involved in this review and in these experiments represents a highly functional, non-specialised version, with minimal elaboration, likely to represent a structure of general currency for routine cremation during the period and area in TABLE 1: Classification of experimental pyres TYPE

ARCHAEOLOGICAL NOTES EXAMPLES -----------------------------------------------------------BOX-TYPE -?no additional timber-structure present stack GP1: simple, effective, economic; satellite log-edged

?Brenig

repeated use possible; heavier lateral logs retain the corpse and burning fuel-load well, decreasing lateral collapse of the pyre;

framed

GP1: secondary

increased stability; higher fuel-load possible; promotes inward collapse;

-additional timber structure present (bracing, or bier-platform) sites in increased stability, and support for FIG 15 the displayed bier; RING-TYPE

GP1 and 3

larger firing possible, more than for utilitarian cremation.

Note: GP indicates Guiting Power round barrow.

Such barrows offer an excellent opportunity to study prehistoric cremation, since those pyre-bases and any associated cremated deposits which have been covered by the subsequent mound remain sealed as left, and are amenable to detailed analysis. Despite operation of natural soil processes, such as panning and bioturbation, many such burnt features remain

Excavated pyre-bases from round barrows (TABLE 2; FIG 15) A good introduction to round barrows of the Bronze Age in Britain, their general structure, burials, rituals, and associated artefacts can be obtained from Ashbee 1960, and Woodward 2000.

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experimental pyres pyre-frame, with two cremated deposits and an inhumation at its margin, lay over the centre of a post ring (Marshall 2007c), all sealed under the round barrow.

relatively uneroded and undamaged, protected under the deepest, central part of the barrow mound. Such protected pyre areas, usually primary or satellite rather than secondary, may not remain as they were at the end of the firing. Pyre sites are often disturbed to differing degrees, by clearance of debris, retrieval of scattered cremated bone, by digging a pit for interment, or by trampling during the process of general preparation of the area for construction of the barrow. The nature and extent of any such disturbance can only be gauged by reference to data from uncleared pyre sites, obtained experimentally.

-Amesbury G71, Wilts. (Christie 1967): A rectangular area of burnt debris, containing a pit with no burial deposit, with a post hole and charred log at the margins, lay near the centre of a post ring (Marshall 2007c) which was established on the truncated mound of the round barrow. -Balnaguard (Perth and Kinross). (Mercer and Midgley 1997) A pyre site of early Bronze Age date, marked by burnt sediment and charcoal (mean thickness 15cm, maximum 20cm), containing cremated bone from several individuals (at least 2 adults and a child), showed signs of repeated use. The surface of the burnt area was partly covered with a scatter of stones, many burnt, perhaps with some traces of partial linear placement. The fuel used was mainly alder, with some oak, beech, hazel, rowan/whitebeam, achieving a high temperature burn, as indicated by the condition of cremated bone. Scattering of char to the SE suggests firing of pyres under NW wind-flow, the direction currently prevailing. The burnt spread was relatively well preserved and may have been covered with turf between firings. Six satellite cists, each containing cremated human bone, lay in an arc around the pyre site, of uncertain relationship but possibly broadly contemporary with the pyre-site. Adult females, children and neonates dominate the assemblage at this phase, with only one male present, in deposits of varying completeness. After the cists were robbed the pyre area was partly surrounded with a ring cairn. A slab cist was inserted through the margin of the pyre site, signs of burning on it indicating that the established pyre area was still in use. The pyre site was sealed under a central cairn, then the space out to the ring-cairn was infilled, possibly leaving the central cist accessible. Several ring-groove palisades constructed around the site contained cremated deposits. No other pyre sites were detected which relate to secondary cremation at the site. Cremated remains of at least 21 individuals are represented at the site.

The overall data on the full range of pyres originally associated with round barrows is of necessity partial, since those for secondary cremation, carried out after establishment of a barrow, and which survive far less well in shallower and less protected marginal contexts, are represented weakly in the archaeological record. Many such peripheral pyre-bases are poorly described, especially in early excavation (Grinsell 1941) and, given their greater exposure many, such as those evident in FIG 15, must have passed unrecognised (Marshall 1998, 2007a). Surfaces beneath round barrows which were sealed by construction of the mound often contain areas of intact burnt surface, displaced burnt sediment, and scatters of charcoal. Much of this debris lies over central areas of the site, which can also contain a burial deposit and, if the rite seen at the barrow is cremation, then these burnt features have been taken to indicate a pyre-site, with surrounding dispersion of burnt debris. If post holes containing burnt material occur within this proposed pyre zone then, if dispersed, they have been interpreted as temporary structures supporting the fuel-load or, if rectangular in plan, as a platform-structure supporting or containing the corpse. Rectangular post structures, themselves often burnt, but without much surrounding burning, have been interpreted as mortuary cubicles, perhaps fired with little additional of fuel, rather than as pyre-related structures, although what they contained, for how long, and why, is not known. Such pyre-base and post combinations have been found on a considerable number of sites, but with perhaps the clearest association and interpretation, at Amesbury G61 and Trelystan N.

-Brenig 40, Denbs. (Lynch et al. 1974): A rectangular setting of four posts, three burnt in situ, forming a possible mortuary cubicle or pyre-frame, with associated burnt timber but with no associated burial deposit, lay at the centre of concentric post rings (Marshall 2007c) sealed under the round barrow.

The following examples serve to illustrate published examples of suggested pyre sites, as sealed under Bronze Age round barrows, and described in terms of visible burning (FIG 15):

-Brenig 42, Denbs. (Lynch et al. 1974): A rectangular setting of four posts, with evidence of burning, representing a possible mortuary cubicle, or pyre-frame, lay at the centre of a post ring (Marshall 2007c) under the round barrow. An area of burnt

-Amesbury G61, Wilts. (Ashbee 1985): An ovate patch of burnt debris, containing stake holes, both scattered and forming a rectangular timber structure, a possible mortuary cubicle or

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experimental pyres which may have been deliberately deposited as token burials. The post features show no coherent pattern, nor particular clustering, although some linearity is possible in places. Their interpretation as representing platforms for excarnation is not supported by osteological data from the site. Two larger posts positioned 4 metres apart and located a few metres from the pyre are interpreted as possible markers. These did not decay in situ but were removed, and a small burnt deposit inserted into the holes.

debris including larger timber, with associated post holes, lay nearby, and may represent another pyre-base. -Letterston 2, Pembs. (Savory 1949): A rectangular patch of burnt debris, containing a cremated deposit and stone capping, lay sealed near the centre, under the round barrow. -Newford, Galway, Ireland. (Wilkins 2008). A later Bronze Age funerary area, unassociated with monumental structures, contained a series of pits, one of which was interpreted as pyre-related, lying within a complex of features which included stakeand post-holes, two of which may represent paired marker posts.

The immediate site is best described as a funerary area rather than a cemetery, as indicated by the lack of fuller and deliberate deposits of human remains, which seem to have been made elsewhere.

Four of the five other pits and 16% of post- or stake-holes contained small amounts of burnt bone,

Another pyre area from the same general region is described in Troy 2007.

TABLE 2: A sample of pyre structures under round barrows -burnt area and post-structure: rectangular post-structures within the burnt area, possibly representing the frame of a box-pyre POST STRUCTURE |BURNT DEBRIS assoc|BURIAL | Ref. Site size(m) posn axis |shape size(m) posn|associated | L W to | L W |type # posn | --------------------------------|-------------- ---|-------------| Amesbury G61 2 1.5 cen N oval 7 5 sur crem 3 mar Ashbee 1985 Amesbury G71 single post NW rect 3 2 mar crem >1 mar Christie 1967 Brenig 40 1.5 1.2 cen NNE irreg 1 1 mar Lynch et al. 1974 Brenig 42 1.5 1 cen NNW irreg 1.5 1.5 mar none Brenig 45 ?present cen ? irreg 1.5 1 cen ? Trelystan N 1.5 1.5 mar WNW irreg 3 2 sur crem 1 cen Britnell 1992 Sproxton 2 posts cen NNW ?rect 2 2 sur crem 1 cen Clay 1993 W.Stoke G39 2 2 W irreg 4 3 cen crem ? cen Gingell 1988 Note: 'W'Stoke' is Winterbourne Stoke G39 -burnt area, possibly suggesting cremation pyres, but with no associated post-structures |BURNT DEBRIS assoc |BURIAL | Ref. Site |axis shape size(m) posn|associated | |to L W |type # posn | --------------------------|-------------------- ---|-------------| Letterston 2 NE rect 2 1.5 cen crem 1 cen Savory 1949 Balnaguard ?WNW ?rect 3.5 3 cen crem >14 cen Mercer and Midgley 1997 Newford E2437 NW rect 4 2 crem ?1 Wilkins 2008 -?rectangular post-structures interpreted as possible mortuary cubicles, with little or no associated burning POST STRUCTURE |BURIAL | Ref. Site size(m) posn axis |assoc | L W to |type # posn | --------------------------------|----------burnt structures Knighton Hill 1 1 cen NW crem ? mar Rahtz 1970 unburnt structures Amesbury G51 2 1

cen

NNE

?

? ?cen

Ashbee 1978

Key: L(ength); W(idth); # number; 'posn' denotes position (as cen[tral], or mar[ginal] of the pyre-base, post-structure, burnt debris or burial in relation to the centre of the barrow area.

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experimental pyres The possible role of death and burial in the wider context of prehistoric society has been further addressed using concepts developed in social anthropology (Parker-Pearson 1993, 1994). Supporting literature for this topic is too extensive and complex to review even in outline here, but interesting isolated references include the following: Olshausen 1892, Olshausen 1908, Schlenter 1960, Ucko 1969, Downes 1999, Oestigaard 2000, Kaliff and Oestigaard 2004.

-Sproxton, Leics. (Clay 1993): An elongate burnt area, half destroyed, with a cremated deposit in a pit dug through it, and a post hole at each end, was sealed under the round barrow. A pyre may have overlain the shallower sub-rectangular pit (2.6m long, 2m wide, and 0.75m deep, with fairly level base), which possibly served to aid up-draught. Pit fill contained burnt pyre-debris and included cremated human bone, with some animal bone, and was considered to have remained undisturbed after a single firing. The fill returned radiocarbon dates such as 729 +/- 177 and 669 +/129 cal. BC, indicating later Bronze Age activity. Pyre-debris contained 685g of bone of which about 11% was identifiably human (skull, teeth, ribs, vertebrae, and limb–bones), with a minimum of one individual represented.

Exposure-burial of corpses is well known from the ethnographic record, as seen in North America amongst the Yankton Indians of the Mississippi area. Here, upright, forked posts form a rectangular setting some 3m long, 1.4m wide, and 2.3m high, supporting a platform for the body (Ellison and Drewett 1971, fig. 2). The somewhat smaller, rectangular settings of post holes associated with pyre-bases under round barrows (FIG 15) may provide a similar facility for temporary display of the corpse before cremation. The pyre itself could have been readily constructed under the platform. Such timber frames have been incorporated within certain of the experimental cremations at Guiting Power, as in the case of box-pyre 2 (FIG 5; PLATE 3a).

-Trelystan N, Powys. (Britnell 1982): The pyre-base associated with burial 4 (Britnell 1982, fig.12, p.155) provides an excellent basis for discussing the excavated remains of small box-pyres, and is worth outlining in some detail. A cremated deposit, representing an adult male and female, placed in a Food Vessel urn, together with a flint object, was placed in a pit 55cm in diameter, and 39cm deep, dug through the pyre-base, which was marked by a rectangular burnt area 1.4 by 2.8m. Within this pyre-base five stakes formed a rectangular setting 1.2 by 1.5m. Associated pyre-debris included charcoal, predominantly oak from mature trees, also from charred plant remains and grass, this latter possibly serving as kindling. Here the stake-setting was interpreted as a possible means of retaining the fuel-load of the pyre, and a temporary support for the corpse.

Examples from the Classical World: lessons from history -accounts of cremation in the Iliad: cremation and barrow construction Two full narratives illustrate the basic stages involved in cremation, from initial gathering of fuel to final disposal of the cremated bones under round barrows. Although the general course follows a common sequence dictated by routine practical issues, the massive scale of the pyre, the number of animals and men sacrificed and added, and some aspects of the treatment of the cremated remains, reflect the high-rank of the individuals dispatched. Cremation of the Greek Patroclus is described in most detail, and although that of the Trojan Hector follows a similar course it is only outlined in summary. These accounts are certainly evocative, especially when read in the original Greek, and provide some background atmosphere for, and serve to prompt thoughts about, events at the barrows which are the subject of this paper.

The different types of timber-structure and associated burning, seen at a sample of excavated round barrows can be listed as follows. The extent of burnt areas in these examples was established by subjective visual means only, not by instrumental measurement, and without clearly stating the nature of burning, whether by direct contact, or as displaced debris. Ethnographic parallels On the basis of purely practical considerations, the minimal form of a pyre consists of a fuel-load, structured for efficient combustion and to retain the corpse placed upon or within it. Upright, ground-fast posts can be added to help retain a higher fuel-stack and also to support a platform for the corpse during the cremation itself, or for longer prior display. The general structure of an effective box-pyre capable of cremating an adult, based on such entirely practical principles, is well documented in the ethnographic record (Dubois and Beauchamp 1943; Hiatt 1969; Noy 2000).

..cremation of Patroclus: Iliad Book 23, The funeral and the games (Rieu 1978, 412-436, especially 415-419). Sequence: collection of oak-wood...fuel moved to the barrow site...construction of a massive pyre...lamentation...corpse laid on top...sheep and cattle slaughtered and corpse covered with fat...carcasses laid on the pyre around the corpse...honey in jars added near the bier...4 horses, 2 dogs, 12 Trojans sacrificed and added to the pyre margins...pyre lit...speech made over the corpse...pyre failed to kindle until winds were

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experimental pyres rites (translated here by the author [AJM] in abridged form):

appeased with libations...pyre blazed all night...wine libations poured and the spirit of the corpse was addressed...procession by Achilles around the pyre...fire burnt low at dawn...ash-bed quenched or sprinkled with wine...corpse-bone collected from the centre...bone placed in a golden vessel, then sealed with a double fat layer and covered with a shroud...stone ring-revetment of the barrow constructed and interior mounded...funeral games took place.

It is the Roman custom to deify Emperors who at their death leave sons or heirs, and the occasion is marked by public mourning and religious ceremony throughout the city. After a lavish funeral, the body of the emperor is buried in the normal manner. Then a wax image of the corpse is laid on a large ivory couch draped with rich coverings, where it lies like a sick man. For seven days people sit in attendance, on the left the senate clad in black, on the right women of rank, without jewellery and in mourning white. Physicians visit the couch daily and pronounce that the emperor’s condition is worsening. When death is formally announced noble bearers carry the couch along the Sacred Way to the Forum where, seated on either side, choirs of women and children from the nobility sing solemn hymns of praise. The couch is then carried out of the city to the Campus Martius, where a square house-shaped structure has been built from large timber beams, its interior filled with fire-wood, the outside clad with rich hangings, ivory statues, and paintings. A second similar but smaller storey with open windows and doors rests on this, supporting third and fourth tiers of decreasing size, to give the impression of a lighthouse. The couch is placed in the second storey and the structure is packed with incense and fragrant offerings. A parade of cavalry displays and, with chariots carrying statues of famous Romans, circles the building. When the funeral rites are complete the Emperor's heir first lights the pyre, to be joined in this by the public until it is well ablaze. From the top storey an eagle then soars, bearing the soul of the Emperor aloft, to be worshipped with the other gods.

..cremation of Hector: Iliad Book 24, Priam and Achilles (Rieu 1978, 437-459, especially 458-459). Sequence: 9-day collection of fuel-wood...corpse laid on the massive pyre...lamentation...pyre fired at dawn...remaining fire quenched or sprinkled with wine at the next dawn...bones collected...lamentation...bones wrapped in cloth and put in a golden chest...chest lowered into a pit and covered with packed stone...barrow mounded over the pit. Covering the corpse with animal fat may have been intended to act as a fire accelerant, but experiments by the author indicate that the effects of such additives are minimal compared with firing a well constructed pyre of dry and calorific wood. Also, the idea of retrieving bone after wholesale quenching of areas of the ash- and char-bed with wine needs re-evaluation. Experiments at Guiting Power show that effective retrieval of highly cremated bone, even as larger items and especially as comminuted fragments, from wet, glutinous ash is very difficult, and that bone separated in this way would certainly need further, time-consuming cleaning. In view of this, such scattering of liquids would perhaps have been more libational than for practical quenching. The importance for successful firing of structuring the pyre to take advantage of prevailing wind is emphasised by early failure in the cremation of Patroclus, an obstacle also noted in modern experiment (Jonuks and Konsa 2007).

The pyre structure (here the rogus) was of open cross-stacked timber filled with fuel-wood (similar to experimental pyre 1), acting to funnel heat chimney-like towards the upper pyre and enable efficient cremation. After the firing, cremated bone was transferred to a more permanent but similarly modelled stone mausoleum (ustrinum). Such ustrina or their pyre-equivalents are shown on commemorative coins (PLATE 8d), typically with a plain podium bearing pilasters, drapery, and festoons at the base, surmounted by the sepulchral chamber with its folding doors flanked by niches and statues, then a third similarly-decorated tier, the top level bearing a statue of the deceased in a chariot with a lit torch at each end. The base of the Ustrina Antoninorum in Rome has a podium 13m square, suggesting a similar size for the pyre. Other details of rites at various levels of Roman society are given in Noy 2000a.

-Roman Imperial cremation: points for general discussion In addition to descriptions of high-ranking cremation from the heroic Greek world given in the Iliad, interesting details relating to Imperial traditions are also provided by Roman historians. For instance, there are references in the Annals of Tacitus to the cremations of Caesar (44 BC), Augustus (14 AD), and Germanicus (19 AD). Herodian of Antioch (c. 170-240 AD) is more expansive in his Roman Histories (Whittaker 1969), where in Book 4, chapter 2, which deals with the reign of Caracalla (188-217 AD), he describes the funeral of Septimus Severus, who died in York in 211 AD, whilst on campaign:

Although far removed from routine practices of the type evident during the Bronze Age in Britain such descriptions of high-ranking cremations are nevertheless relevant in that they prompt certain

Herodian relates how his sons Caracalla and Geta carry his urn to the mausoleum in Rome, and then provides a general description of Imperial funerary

7

experimental pyres existence of dedicated cremation grounds at some distance from the place of interment. For instance, pyre sites for secondary cremated deposits made around and into the upper levels of round barrows may have existed within the immediate vicinity or more remotely, within designated areas, perhaps nearer direct settlement.

questions about structure and ritual which are of more general application, providing a case in point for discussion: ..In the description above we see what seems to be a case of ceremonial cremation involving a body-substitute, preceded by separate and more private cremation and disposal, perhaps not surprising in this case given that the death of Septimus Severus occurred so far from Rome. There are other isolated references in Herodian (chapters 8 and 13) to conventional rites where the body was more immediately available for display and cremation. This narrative should alert us to the possibility of token cremation, from full substitution of the body to involvement of body-parts only, a point stressed again for the Neolithic and Bronze Age British context in Duffy and MacGregor (2008).

..The scope for ceremony accompanying cremation should be emphasised, especially in cases involving higher-ranking or otherwise significant individuals, activities of a type not immediately involving the cremation itself but taking place beyond the immediate area of the pyre. For instance, circular structures around certain cremation sites would provide a suitable setting for processional and other action. In the above description, and in those for the funerals of Patroclus and Hector, the contribution of ceremony outweighs the actual cremation event itself.

..The form of the pyre adopted (the rogus) indicates that such structures need not be entirely functional and minimal, but could be elaborate, decorated, and furnished, far in excess of what was required for reduction of a corpse, such embellishment reflecting social standing and the need for public spectacle. This raises the possible existence within the prehistoric context of larger and more elaborate pyre-structures associated with funerary monuments for individuals of status.

APPLICATION OF ARCHAEOLOGICAL AND EXPERIMENTAL DATA TO INTERPRETATION OF ANCIENT CREMATION AND SURROUNDING RITUAL Reduction of a corpse to clean bone by cremation renders more accessible to participation and ritual the lengthy process otherwise undergone during prolonged periods of exposure or temporary inhumation, condensing it to a matter of hours. The firing phase of cremation certainly provides a far more spectacular and dynamic focus for processing of a corpse, as a specific event giving added visual impetus to group observation, collaboration, and participation in ritual activity. The role of ritual and the changing perception of human remains by participants during such events are discussed more fully in Williams 2004, Jonuks and Konsa 2007, and Sorensen 2009. In view of this heightening of experience, when analysing pyre sites, the possible impact of ritual on structures and processes must be clearly borne in mind in discussing features which depart from the functional norm.

..When discussing such elaborate pyres it is necessary to distinguish between the full pyre-structure and the location of the combustible pyre-cell within it. In the above description, and in most of the cases discussed in this analysis, the two appear to coincide and rest directly on the ground. But there are clear ethnographic cases where the combustible chamber is not on the ground but well elevated in the pyre-structure, further adding to the spectacle and its potential for mass viewing (PLATE 8c). Firing such an elevated structure would result in a much reduced impact on the archaeological record. Direct burning over the land-surface would be far less and the event would leave only spreads of charcoal and ash-rich debris, plus any surviving unretrieved pyre goods and residual cremated bone scattered amongst any ground-fast features left by supporting timber or stone structures. This should all be borne in mind when interpreting funerary areas where cremation took place, especially at more impressive monuments, since pyres need not be marked by a directly burnt rectangular area of sediment and stone but could leave far more ephemeral traces. Such possibilities further indicate the need for recording pyre-sites and candidate areas not only visually but by magnetic prospection, all too rarely carried out (Marshall 1998; Cf: FIGS 15 and 17).

The extent of what can be inferred about ancient cremation from the archaeological record is obviously limited because almost the entire pyre and its crematable load has been incinerated, leaving only a few earth-fast traces, and many of these only detectable instrumentally. Besides these ground effects, those few residues from the pyre and its contents which do survive the immediate cremation can be left variously in situ in various states of disturbance, scattering, and clearance, or collected then buried or removed from the site, leaving many imponderables. The plane of contact between the archaeological record and the original structure is therefore weak and very incomplete, connected only by a few ephemeral basal features.

..Cremation and subsequent deposition of remains can be well-separated spatially, suggesting the

Ritual, although the most tenuous aspect of interpretation, must certainly be considered, since it

8

experimental pyres is restricted mainly to pyrotechnic and temporal data on the immediate cremation process and its aftermath, and to the relationship between parent pyre structures and the patterns of burning and scattering they cause over the underlying ground surface. Information on the ability of various incombustible inclusions in the pyre to survive as a residue is also important.

is evident that cremation and deposition of human remains, rather than being purely utilitarian operations, fit within a broader sequence of structural and ceremonial activities which relate to establishment and operation of barrow monuments. The act of cremation can not necessarily be regarded as the functional minimum required to dispose of a corpse, but would be expected to interact strongly with ritual, and become modified by it, in many ways which are unlikely to be structurally apparent.

Activities surrounding cremation can be listed in their approximate order of occurrence as follows (TABLE 3), noting those stages which afford particular opportunity for interaction with ritual, and the extent to which each stage may be amenable to archaeological and experimental investigation:

Experimental cremation and its interpretation must be conducted with this wider context, and with the limitations imposed on use of evidence clearly in mind. The main contribution from such simulations

TABLE 3: The outline sequence of events required to perform a cremation DATA from TYPE OF ACTIVITY RITUALS COMMENT (expanded below) expt arch undertaken present ---------------------------------------------------------------------------Type of ritual possibly present: -preparatory + ++ choice of pyre-site ** appropriate location +++ +++ preparation of pyre-site * turf stripping, post structures? +++ +++ selection of fuel-wood * choice related to status? +++ ++ construction of pyre ** orientation merely functional? ++ + preparation of corpse *** whole, fresh, dried, defleshed? ++ + display of corpse on pyre ** post-structures present? ++ + placement of corpse in pyre * on, in, perhaps under? ++ + placement of pyre-goods ** wide range possible -auxiliary + ++ auxiliary rituals *** feasting activity detectable? -attendant +++ ++ firing of pyre ** conditions, solar mimicry? -final +++ +++ collection of cremated bone ** care taken, retention? +++ +++ clearance of ash-bed * extent, remote dumping? +++ +++ deposition of cremated bone *** crushing, urning? +++ +++ deposition of grave goods *** items fresh or from pyre? ++ +++ encairnment *** dedicatory aspects Key: + to +++: what can be concluded about each stage of the original activity, by experiment or from excavated archaeological structures, graded from lower to higher reliability; * to ***: the degree of ritual likely to be associated with each stage of activity.

be assessed from archaeological stratigraphy, where this initial stage further emphasises the care taken with the site chosen for the event. The extent to which clearance and preparation of the site is structurally detectable can also be established by experiment, placing pyres on a range of natural, and cleared substrates.

The choice of pyre-site is likely to have been determined jointly by environmental considerations, such as availability of materials or degree of exposure to the elements, and the need to use a setting appropriately placed in relation to settlement or to existing areas of funerary activity. However, those pyre-bases which have survived to be investigated need not be a representative sample of pyres built, but only of that small fraction preserved by sealing under subsequent barrow structures, these perhaps even atypical structures used in special circumstances. Other dedicated pyre-grounds are possible, away from monuments such as barrows.

Rather than merely using an existing ground surface as a base for the pyre, construction of an artificial surface is possible. For instance, an elevated or otherwise prepared pyre-platform incorporating turf, soil, clay, and stone would provide further enhancement of the pyre setting. Examples of this practice are common in the ethnographic record, and are noted from the Classical Mediterranean. Such

Evidence for preparation of the pyre-site can often

9

experimental pyres therefore possible that hazel had some symbolic meaning perhaps connected with resurrection or rebirth, possibly a precursor of the tradition seen in early Christian continental Europe (Henricksen 2009). A connection between the social status of crematee and the type of fuel-wood used is also possible: the Roman author Tacitus relates that important men were cremated on chosen types of wood. However, at Brudager it was not possible to establish any connection between archaeological status and specific types of fuel-wood.

structures have been suggested in the central Swedish area during the later Bronze Age (Kaliff 1994). At Cladh Hallan (South Uist), a later Bronze Age to early Iron Age settlement (Parker-Pearson et al. 2004), a terraced row of roundhouses, which contained underlying burials, also included one hut associated with cremated human bone scattered within and over a platform just outside. It has been suggested that this hut may have housed specialists in funerary ritual serving the pyre facility outside. Raising the pyre on a basal platform of timber would also add to the spectacle of cremation, and still further reduce any traces left in sediment by burning, since larger basal timber might remain largely unburnt, and the whole structure could be easily cleared. Such structures separate the basal burning of the pyre from the ground surface, and if demolished after the cremation would of course largely obliterate the pyre site, reducing it to a scatter of displaced burnt material.

The construction of pyres and their properties during use can both be investigated in detail experimentally, and related to the remains which they leave. Such correlations can then be used to discuss the nature and operating conditions of ancient pyre-structures, as suggested by comparison between experimental and ancient burnt pyre-bases. The extent and content of pyre-debris from archaeological contexts surviving in situ, and the nature of the burning over an underlying pyre-base, can all be matched against experimental data to help interpret such remains.

The selection of fuel-wood is probably more of a choice made on practical than on ritual grounds. The range of timbers and other fuel used can be assessed from analysis of charcoal surviving in ancient pyre-debris, whilst the nature, condition, and effectiveness of such fuel can be readily tested by experiment.

How far ancient pyre-structures deviate from standard forms established by experiment can be assessed, and used in discussion of aspects of ritual at the site. Experiment can certainly determine the range of pyre-structures which are practical and minimal for cremation, as a basis for assessing those from under barrows, and identifying any possible abnormality.

The choice of fuel for cremation may be based on a variety of factors dictated by circumstance, practical considerations, and ritual significance: its availability, its calorific suitability for effective cremation, and any perceived magico-religious properties. Analysis of charcoal from pyre sites should give some basis for discussion of the balance between these options, indicating random or specific selection of fuel, and use of prime timber or scrap. For instance, the predominance of oak and ash charcoal, both highly exothermic, in areas where these were common might, suggest that availability and practicality were prime factors in choice. Typically, calorific wood of common local type forms the basis of the fuel-load. For instance, at Ballybar Lower (Carlow) fuel-wood was alder and oak with some Sorbus, an appropriate mix for achieving efficient cremation (Troy et al. 2010). At Balnaguard (Perth and Kinross) fuel was predominantly alder, with some oak, beech, hazel and rowan/whitebeam present (Mercer and Midgley 1997). However, at Linga Fjold (Orkney) fuel was predominantly turf, far less inherently calorific (Bunting et al. 2001).

A corpse rich in bodily fluids needs high and sustained temperatures to burn. On pyrotechnic grounds it seems reasonable that any particular location and orientation for an experimental or ancient pyre would be chosen in an attempt to optimise air-flow, thereby promoting combustion, avoiding partial burn-out and possible collapse, and achieving efficient cremation. In the case of ancient pyres the axis may also have been selected for additional ritual reasons, if aligned E-W for instance, perhaps reflecting passage of the departed towards the west, a direction commonly associated with death. Analysis of axial directions for ancient pyre-bases, and assessment of additional distortions induced in patterns of ground burning by their ventilation under prevailing wind, could provide a point of entry for discussion of the actual basis for their alignment. Final preparation of the corpse can be varied experimentally, and together with knowledge of the pyre-structure can be used to interpret characteristics of ancient pyre-bases and cremated deposits. Experiment can determine the nature of pyres which are adequate for disposal of single or multiple corpses, these being in original, desiccated,

Any marked deviation from common and optimum species could indicate operation of ritual constraints on selection. In the later Iron Age cemetery at Brudager (Denmark), for example, hazel charcoal dominated the pyre debris rather than more commonly available species like oak and birch. It is

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experimental pyres ash-bed would need to be demonstrably intact, a rare occurrence, since retrieval of bone and clearance of debris, often very thorough, were the norm.

or de-fleshed condition, and generate informative sets of residual remains. Since it is difficult to infer original condition of the corpse from cremated residues, in the absence of clear evidence to the contrary the unmodified body would be the case by default. Occasional reports of processing do occur however: for instance, evidence from Early Iron Age Norway and Denmark has been used to suggest that in some cases quartering of the corpse had been carried out before the cremation (Holck 1997).

Consideration of the high temperatures which are required for efficient cremation suggest at the outset that information on placement of pyre-goods is likely to be very partial, with only the most resilient materials surviving the event, and usually in very degraded, erodable form. For instance, highly oxidised and fragmented metals such as copper have increased solubility and are likely do disperse readily, even under well-sealed less aerobic conditions. Detailed ancient clearance of ash-beds is likely to reduce still further the chances of retrieving even that fraction of any pyre-goods which did survive the cremation. The need for very detailed search and careful identification, with this inherent bias firmly in mind, applies both to ancient, and to experimental contexts.

Distinct display of the corpse on a pyre or prior to its construction is often suggested in the archaeological record by the existence of post or stake holes surviving within the pyre-base, possibly indicating supports for a rectangular timber frame (FIG 15). Experiment can assess the adequacy of such timber structures for this purpose, their influence on combustion and downward progress of the corpse into the pyre, and how far such a frame might anyway be required for more practical purposes, such as retaining the fuel-load. Experimental work to interpret pyre-related post constructions from the later Bronze Age to later Iron Age period in Denmark stresses their importance in stabilising the pyre during the initial phase of burning, a time when the raised superstructure is more vulnerable to partial collapse than when structures have burnt low (Henricksen, pers. comm.).

Analysis of survival rates for different materials can readily be undertaken by experiment. In appropriate cases, as for instance with copper-alloys, micro-structural changes induced by cremation can be determined, thus helping to distinguish items which may have been through the pyre from unburnt objects which were introduced to the context separately. Since they may well leave little or no trace in the archaeological record, the occurrence of any auxiliary rituals, carried out before, during, or after cremation is difficult to establish. However, firings of experimental pyres can establish the extent and nature of contact-burning and scattering of debris generated by cremation alone, where no other ritual of a type likely to leave either burning or scattering of food residues for instance, has taken place. From this base-line some general assessment can be suggested for likely levels of auxiliary burning and scattering in the archaeological context, but establishing its timing in relation to the actual cremation would depend on the existence of detailed linking stratigraphy, usually absent. Any discussion based on such subtraction of functional cremation-related burning from observed patterns would be greatly complicated by ancient clearance of the pyre area, removing or at least disturbing burnt surfaces, and scattering them elsewhere.

The extent to which the bases of such posts become burnt by experimental cremation might also be used to help establish whether these frames preceded, formed part of, or followed the cremation event, questions relating to interpretation of ritual. Experimental work in Denmark has confirmed that, despite intense burning, the shielding effect and thermal inertia of the ground stops charring near the surface of the soil, raising doubts about the ability to distinguish between these options (Henricksen, pers. comm.). The corpse and its furnishings could be displayed in more spectacular form by elevation within a tall pyre-structure, as shown by current practices in parts of Indonesia and by depictions on Roman coinage (PLATE 8c,d). Some indication as to the original placement of the corpse within an experimental pyre, including more precise details of the direction of its head-end, could all be determined by examination of an intact ash-bed, the nature of the scatter of cremated bone within it, and its condition. The corpse could be variously placed in the pyre, from its upper to lower levels, leading to different efficiencies of cremation and degrees of scattering on descent of cremated bone through the pyre. Whether the body was prone or crouched might perhaps be detectable in the resultant scatter. For similar interpretations to be made from archaeological contexts, the ancient

The intensity of firing in pyres can be measured experimentally, and matched against resultant burning of ground surfaces, scattering of debris, and to the number of corpses which could be cremated thereon. Matching ancient pyre-bases, and any evidence for the number of individuals of known sex, age, and size represented in associated cremated deposits, against such experimental data, allows assessment of any surplus firing capacity. Any distinctly excessive capacity might perhaps suggest

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experimental pyres some festive component, beyond strictly practical needs.

being an important, but largely unrecognised contribution.

Methods for collection of cremated bone can be investigated experimentally and applied to analysis of that from archaeological contexts, assessing such questions as the ease and extent of retrieval, the possibility of selection of items, and the evidence for any subsequent processing of bone before deposition, such as quenching or crushing. Data can be readily obtained experimentally, under defined conditions, regarding changes wrought in skeletal material and other body tissues, throughout the combustion sequence from unburnt corpse to final cremated residues, and used in assessment of scatters over ancient pyre-bases, and in analysis of related cremated deposits.

DEFINITION OF TERMS There is considerable imprecision and variation in the terminology which relates to the cremation process, as used in technical reports on excavation of related structures, and even in recent reviews, as for instance McKinley 1997, p.130. Terms such as 'cremation deposit', 'cremation burial', 'pyre cremation', or 'cremation-related feature', found widely in the literature, are not used here, because of their ambiguity. Consequently, the terms and their components which are used in this series of experiments, and during further application to related archaeological contexts, are standardised as follows (in bold type), with clear sub-division of structural, and functional aspects:

The retrieval of bone itself could have been ritualised: for instance, there are examples from 19th century Japan where cremated bone was picked out by relatives using chop-sticks according to special rules (Olshausen 1908).

>PYRE-STRUCTURE: the entire construction in which cremation takes place. >PYRE-CELL: that combustible part of the pyre directly involved with cremation, and which may form only part of a larger and more elaborate pyre-structure. In the case of standard box-pyres these two elements coincide, but for larger pyre-structures they need not (PLATE 8c,d).

The extent to which ancient pyre-sites have been changed before sealing, by clearance of the ash-bed or by truncation of the pyre-base, can only be assessed against intact features obtained by experiment, and this is critical to interpretation of data from archaeological contexts. The state of an ancient pyre-base relates to events which immediately follow cremation, and it is important to distinguish between specific clearance, for instance by scraping, and an accumulation of damage, as would be caused by general trampling sustained during retrieval of items and construction of an overlying barrow mound. Identification of such conditions relate to the importance placed on the area used for a cremation, often placed at the centre of a subsequent barrow, and the priority given to sealing it in good condition under the mound, again impinging on discussions of ritual involved in encairnment.

The pyre-cell can vary in location, being either grounded (resting on the ground), perched (raised slightly clear of it on basal timbers or stonework), or elevated (raised well above it in a more elaborate framework). >PYRE: the pyre-cell plus any associated sub-structure. -superstructure: components: the fuel-load, consisting of an interlocked lattice of major structural timbers and smaller essentially non-structural timber; any standing or ground-fast post-structure which serves to support the pyre-cell, and which may form a platform-structure for the corpse if this has not been provided by a separately-placed bier. This superstructure can be classified by shape, for instance as a box-pyre, or ring-pyre, with further sub-division to component types (TABLE 1).

Details surrounding the deposition of cremated bone can be obtained from processing such material produced experimentally. Determination of the time taken to separate bone, and to what detail, allows some appreciation of the level of care taken with ancient remains. Establishing what constitutes a full complement of cremated bone, what proportion is irretrievably lost during firing, or missed during collection, is directly applicable to interpretation of ancient remains as being full, partial, or token. Information on the extent of thermal shattering of bone by cremation can be used as a background to assess the degree to which ancient remains have been further prepared for burial, as by crushing or quenching for instance. The extent to which non-bone bodily material survives cremation can also open up the possibility of carbonised soft-tissues

-sub-structure: components: all features penetrating into the ground under the pyre, such as any scoop made at the margin to aid primary ignition, any driven or set post-holes which support a post-, or platform-structure in the pyre. These features are distinct from those of the underlying pyre-site. >PYRE-SITE: the area on which the pyre was constructed.

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experimental pyres -residual pyre-debris: that which remains within the area of the cooled ash-bed. ..primary: without removal of any items; ..depleted: after removal of items, either as clearance of the bulk without selection, or after selective removal of items, such as larger semi-burnt timbers and charcoal, cremated bone, or pyre-goods.

-unaugmented: where the basal ground area to be covered by the pyre remains unmodified (Cf: pyre-base and ash-bed). -augmented: where there is construction of a pyre-platform of earth materials (stone, turf, soil, or clay), or of timber, to provide an elevated setting for the pyre, which is distinct from the structure of the pyre itself (Cf: the platform-structure which forms part of the pyre).

-deflated pyre-debris: combustion products from cremation (gases, vapour, and finer particulates) removed by rising heat and prevailing wind-flow.

-ablated: where the ground surface under the pyre has been prepared by de-turfing, or further removed to contain it within or position it over a depression.

-scattered pyre-debris: residual pyre-debris which has been generally displaced beyond the ash-bed, either incidentally during clearance and subsequent construction activities, or perhaps as a deliberate act during funerary ritual.

In the case of experimental pyres, the limits of the pyre-site can be clearly seen but, in the case of excavated pyre-bases, the location of the pyre-site can only be inferred from analysis of the surviving pyre-base.

-redeposited pyre-debris: debris which has been taken from the ash-bed and deliberately placed in a separate location, either simply as practical disposal or with some ritual intention.

>CORPSE: the cadaver and any coverings as prepared for cremation, but with any closely associated items considered separately (Cf: primary pyre-goods).

>CHAR-BED the pile of pyre-debris at a late stage of burning, with fuel-wood and structural timber reduced to burnt fragments and embers.

>PYRE-GOODS: items of any type placed as offerings, and burnt on the pyre: -primary: wrapped with or placed immediately on the corpse, before cremation; -satellite: placed separately from the corpse, but within the pyre, before cremation; -secondary: placed to be near or in the pyre during or immediately after cremation.

>ASH-BED: components: the pile of pyre-debris left after burning has finished, depleted of all combustibles, which covers the pyre-base, and marks the location of the original pyre-site; the marginal zone of scatter extending beyond. >PYRE-BASE: burnt features, either visible or detectable only by instrumental means, resulting from cremation, which appear over and are induced within the upper layers of the ground-surface, under the ash-bed and its marginal zone.

>GRAVE-GOODS: items which have not been burnt on the pyre, but which are placed after the cremation with the cremated deposit: -primary placed immediately with the main part of the cremated deposit. -satellite: placed close to, but not with, the cremated deposit.

>CREMATION: the process of combustion of pyre-structure, corpse, and pyre-goods, from the time of ignition to formation of the cooled ash-bed. A cremation is not 'the actual pyre with the burning corpse and any attendant artefacts/offerings upon it' (McKinley 1997, p.130), but the process itself.

>PYRE-DEBRIS: All detritus generated by cremation. This does not include any elements of the underlying baked pyre-base, which is an effect of radiation rather than a product of combustion, and is hence considered separately. The term 'pyre-debris' refers to the material, and the term 'ash-bed' to the feature consisting of pyre-debris.

>CREMATED DEPOSIT: that fraction of human and/or animal bone, enriched with pyre-debris, which was deliberately selected for subsequent deposition or burial. The term 'cremation deposit', in widespread use, is grammatically meaningless.

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experimental pyres >CREMATION-RELATED RITUAL: those activities of a ritual nature directly involved in the preparation, combustion, subsequent processing, and deposition of all material relating to the pyre-structure, its corpse, pyre-goods, and grave-goods.

Group 1: fuller experimental programmes

Rituals of four main types can be distinguished: -preparatory: prior to ignition of the pyre; -attendant: during the cremation process; -final: after the cremation, concerning collection, processing, selection, possible retention, and subsequent interment of cremated remains; -auxiliary: activities supporting but not directly involved with the cremation, taking place either before or after it, such as any associated feasting, ceremonial activity, other firings, scattering of artefacts, construction of features such as hearths and pits, or deposition of artefacts.

Pyres were of two main types: [Henricksen 1991, figs. 1-2]: pyre: stack-pyre about 2.45 x 1 x 0.6m high; firing reached over 1000oC under end-on wind and achieved complete cremation; burnt area planned as a central concentration of bone within the ash bed, surrounded by a red burnt margin; corpse: pig (50-65kg) placed under logs in the upper third of the pyre and cremated effectively after 5h to produce easily retrieved bone fragments;

-Denmark 1989-1992 (Henriksen 1991, 1993; experiments carried out at Lejre and Hollufgarde, Odense, Denmark; overview of programme Henriksen 2008; 2009).

[Henricksen 1993, figs 1-4]: pyre: fuel-load of about 1m3 of timber, about 1m across and 1.5m high stacked within a triangle of three uprights or rectangle of four to support the pyre during the early stages of firing; built over a small pit to allow aeration of the fire; corpse: pig placed within the upper pyre, but in experiment 2 the corpse was placed under the pyre, (Henriksen 2008, 10).

Section 2: EXPERIMENT OTHER EXPERIMENTAL PYRES There are numerous other references to construction, firing, and analysis of experimental pyres. A great many of them have been carried out rather more specifically for osteological investigation of cremated remains than analysis of pyre structure and ground effects. Much work has been carried out, for instance, on those changes which various types and conditions of bone undergo during cremation, and the effects of varied environments and treatment, more often in laboratory-controlled cremation than in timber pyre structures (e.g: Manye Corriea 1997; Walker et al. 2008). Some experiments have indeed placed a greater emphasis on analysis of pyre structures (e.g: Henrikson 1991, 1993, 2008). Far fewer studies have emphasised issues of prospection to the same degree, presenting more detailed analysis of pyre structures, environmental conditions during firing, and accurate mapping of ensuing ground-effects (Marshall 1998, 2007a). Because of the spectacular nature of cremation there has also been a recent trend towards mounting such events for the purposes of public 'edu-tainment', an excellent motive, but usually unmatched by scientific content.

For both types: purpose: analysis and interpretation of Bronze and Iron Age burials of cremated material in Denmark; conclusions: much empirical data on the conditions of cremation; cremated deposits of Bronze Age, and especially early Iron Age date, in pits, represent graves not pyres; triangular or rectangular post settings from late Bronze Age and Iron Age cemeteries could represent the remains of pyre constructions. -Estonia 2005 (Jonuks and Konsa 2007) pyre: box-pyre (approx. 1.75 x 1.2 x 0.85m high) of cleft birch logs stacked in layers alternately along and across, with a layer of stone laid under the pyre for better ventilation; two grooves left in the pyre were filled with brushwood to aid initial ignition; no timber frame present but supporting diagonal shoring was added around the margin; single experiment but part of a broader investigation of burial practices; time-course of cremation is given, but no environmental data or analysis of ground effects reported. corpse: adult pig (100kg) placed on top of the pyre on a half-woollen blanket, with added pyre-goods of metal, bone-antler, shell, and pottery illustrated before and after cremation; purpose: comparative study of burial practices by simulation of open air burial, stone cist burial, and cremation; analysis of factors affecting the cremation process, including the pyre structure, corpse, and pyre-goods.

This is not the venue for a full review of experimental work, but examples can be found in the following references, a very reduced bibliography: Piontek 1976; Graslund 1978; Lange et al. 1987; Werner 1990; Lambot 1994; Sigvalius 1994; Becker et al. 2005). The following projects are given in more detail to provide examples of current trends and to provide specific points of comparison with the experimental work outlined in this paper.

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experimental pyres balanced on top of the pyre, required it to be restrained with poles as it became displaced and started to roll off as the pyre burnt. Correct structuring of the pyre and embedding of the corpse firmly in its uppermost level, or provision of a supporting timber frame, would help avoid such problems. Unfavourable orientation of the pyre in relation to prevailing wind caused further problems, in that strong wind carried heat away from the body.

Group 2: smaller case studies -Archaeolink Centre, Oyne, Aberdeenshire, Scotland: September 2004 (Sheridan 2009). pyre: type and dimensions unknown; no timber frame noted; single experiment; no temperature data nor analysis of ground effects reported; corpse: 6 month old pig placed on top of pyre; purpose: examination of the effects of burning on a faience bead, accessory vessels and bone pin, related to analysis of a cremated deposit of the earlier Bronze Age from Findhorn, Moray, Scotland.

All this combines to emphasise the skill with which many ancient cremations were carried out, judging by the final highly oxidised condition of much burnt bone from archaeological contexts. Such skill in execution would be further tested during inclement seasons of higher rainfall and wind, especially if using damp fuel.

-St Fagan's National History Museum, Cardiff, Wales. (McCarthy 2009) pyre: fuel-load of cross-stacked timber resting on a log-edged ground course (approx. 2.5 x 1.5 x 0.8m high); mixed hard and softwood logs with hay and brushwood kindling; no timber frame; single experiment; no data on environmental conditions or ground effects reported; corpse: sheep/'lamb' placed on top of pyre; purpose: examination of the effects of pyre stoking and dowsing with water on fracturing and fissuring patterns in retrieved cremated bone, with especial reference to possible Anglo-Saxon practices.

Ancient cremation may have been an operation carried out by specialists who qualified on ritual or technical grounds, rather than being done on a more routine domestic basis (Holck 1997). Given general necessary skills in timber felling and fire building amongst the population, and the comparative ease of cremating a corpse compared to use of fire for production of pottery and metalwork, it seems unlikely that the practical side would have required professional management. However, it is far more likely that specialists would have been required for ritual aspects, to handle and prepare the corpse, and to deal with the aftermath of the cremation process.

Group 3: events for public education -Festival of British Archaeology 2009 National Museum of Wales pyre: box-pyre of cross-stacked timber (approx. 1.5 x 1.2 x 1.2m high); no timber frame; single experiment; no temperature data or analysis of ground effects reported. corpse: pig placed on top of pyre; purpose: public education.

EXPERIMENTAL CREMATION at GUITING POWER General strategy Research into Bronze Age pyre technology was planned by the author from the outset as an integrated programme to investigate a series of experimental pyre-structures of prehistoric type. This included replicate firings under varied conditions to enable detailed analysis of the process of cremation and the nature of resultant debris and ground-effects. Longer-term monitoring of physical changes induced in such pyre-bases after burial, and comparison between experimental simulations and excavated controls at round barrows linked the project directly to the archaeological record.

INITIAL THOUGHTS ON THE CONSTRUCTION OF EXPERIMENTAL PYRES In order to ensure effective and dignified cremation the need to construct, fuel, and ventilate the pyre adequately, and provide stability for the corpse, all at the outset, is illustrated well by the experimental pyre of Jonuks and Konsa (2007: time course given in table 2). Here the original 2m3 fuel-load was found to be insufficient for full cremation, and had to be supplemented at three mid to late stages during the 6 hour course of firing. In view of this problem the progress of cremation was slower than for intense single-phase experimental pyres 1 and 2 at Guiting Power, and the cremation process correspondingly less efficient, although after 3 hours most bones were nevertheless heavily cremated. Under such conditions of reduced and extended combustion the survival rate of pyre-goods was also higher than for the experiments at Guiting Power (Jonuks and Konsa 2007, table 3). In addition, location of the corpse,

The preliminary project work on experimental pyres was carried out in two stages. An initial, somewhat simplified, more regular box-pyre of framed type was fired to determine and solve any technical or logistical problems (pyre 1: FIGS 3,4,7,8,12; PLATE 1). This initial pyre, constructed from a large mass of dry, highly calorific wood, arranged to ventilate efficiently, and fired under dry, fairly windy conditions, was also deliberately intended to provide an upper bench-mark for high-temperature cremation, against which other experiments in the series could be compared.

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experimental pyres reflects the situation seen under most round barrows, which suggests single use of an unburnt pyre-site, with primary cremation representing a brief dedicatory event, soon sealed under the ensuing barrow mound. Repeated cremations on or around the same spot would be expected to produce composite pyre-bases, larger and more deeply burnt, the components of which would not be readily separable. This latter situation might be expected for cremation carried out more routinely in any localised cremation-grounds which lay beyond the barrow, of the type which may have produced cremated remains appearing more superficially in barrows as secondary deposits. Experimental determination of burnt basal sediment produced by a single, 'standard' pyre would enable such larger, or multiple firings to be identified and discussed with more confidence.

This pyre was followed, after full analysis of existing results, by a second, more naturalistic framed box-pyre, with structural additions (pyre 2: FIGS 5,7,9,12; PLATES 3a-f). Dividing the project in this way also enabled the first pyre-base to be analysed by excavation, whilst retaining the second base intact, as subjected only to instrumental analysis, to be buried and monitored as part of a long-term experiment. Having covered many of the basic objectives of the project with these two experiments, investigation of a series of other pyre-structures took place after this, as further questions became evident. Investigation of other forms of box-pyre followed, including simple stack- and log-edged types. Experimentation turned to the operation of ring-pyres, larger structures, examples of which also appear under round barrows. Including replicates, a series of nine pyres were fired under experimental conditions.

Full monitoring of conditions during firing, to give complete sets of data on such variables as temperature change and composition of exhaust gases, was carried out for pyres 1 and 2. During other experiments, the very similar operating conditions which obtained were tracked by fewer readings made at strategic points. After the firing, all pyre-bases were investigated with the same degree of resolution, providing comparable data from visual examination, geophysical mapping, and except for those deliberately reburied for later investigation, from excavation.

Experimental cremation was largely confined to consideration of smaller pyres, perhaps representing the type in routine, utilitarian use for prehistoric cremation. These were sufficient for a single adult-sized corpse, although it would certainly have been possible to dispose of at least two adults, with high efficiency, on each experimental pyre, given the intensity of combustion achieved. Only on pyre 2 were two individuals cremated, each prone and side-by-side, representing an adult and infant, the combination found in the primary cremated deposit at Guiting Power 3 round barrow (Marshall 2007b).

Examples of the types of pyre investigated experimentally which are included in this paper, are as follows (TABLE 4):

Furthermore, only the simplest case, that of a single cremation on fresh ground, was considered. This

TABLE 4: Selected pyres from the programme of experimental cremation PYRE TYPE

sub-type

1 2 3 4 5

framed framed log-edged stack -

box box box box ring

Replicate PARALLELS: expts. pyres at GP1 2 1 1 2

secondary secondary satellite primary

FIG

PLATE

3 5 10 10 11

1 3a-f

Guiting Power 3, and at other round barrows, including Carneddau I (Gibson 1993). Details of timber used to construct the pyres came from review of charcoals found with cremated deposits from round barrows widely within southern Britain, and presumed to represent debris from the pyre.

The form of box-pyre used in initial experiments (pyres 1 and 2) was based on consideration of ethnographic parallels, and on preliminary assessment of pyre-bases excavated under round barrows (FIGS 15-17). The form of pyre 2 was modelled fairly directly on structures indicated by the well-preserved pyre-base at Trelystan (FIG 15; Britnell 1982, fig.12, p.155), with its rectangular post setting suggesting a pyre frame, perhaps bearing a platform supporting the corpse. Examination of possible ground-effects from deposition of hot pyre-debris in small pits was related to such pits at

Although it was possible to replicate prehistoric pyres accurately in terms of structure and materials, unfortunately it was not possible, for legal reasons, to complete the parallel by using human corpses for the cremation, although this was the original intention.

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experimental pyres -extent, thickness, and pattern of visible and magnetic changes induced in the surface under a pyre of precisely known properties, operated under closely-defined conditions; -the vulnerability of pyre-bases to destruction during ancient clearance, interment of cremated deposits, and disturbance associated with subsequent mounding activities; -assessment of the extent to which an intact buried pyre-base might be detected at the surface by magnetic gradiometry or magnetic susceptibility (MS) survey; -further definition, by long-term experiment, of the changes which a pyre-base might undergo during burial under a barrow.

The objective was then redefined: to characterise a pyre CAPABLE of cremating a human adult. Use of an animal substitute enabled adequacy of the pyre for cremation to be assessed, its structural behaviour to be monitored, and the overall pattern of residue generation to be observed. The animal corpse was seen as a means to meter the adequacy of pyre intensity, and formed part of the instrumentation, rather than providing a source of cremated bone for detailed forensic analysis. A suitable 'unit-corpse' was certainly required as part of the pyre-structure, to ensure realistic collapse of the burning pyre under the combined weight of both body and timber. An experimental pyre, if it is to provide a viable simulation, certainly needs to be matched against the mass of wet tissue comprising a corpse: without a corpse it remains a fire. It should be noted that the main emphasis of the research was not on analysis of cremated remains, but on examining the relationship between pyre structures and features left in the archaeological record by their firing. The nature of bone and pyre-goods after cremation, although investigated, is somewhat incidental to the main objective of the programme.

Choice of an appropriate structure for experimental pyres Box-pyres seemed a reasonable structural choice, since they are suggested by the generally rectangular or ovate burnt areas revealed by excavation under many round barrows (FIGS 15-17). Such pyres are also well attested throughout ethnographic literature, from sources as varied as decorated pottery from ancient Greece, 17th century woodcuts from Europe, and verbal descriptions and drawings from 19th century India and Australia. The box-pyre structures adopted for the first two experiments were both of framed-type, the first without additional timber support for the pyre and corpse (pyre 1), the second with this added (pyre 2). Further experiments included box-pyres of simple stack, and log-edged stack types. Ring-pyres were also fired to provide comparative data on excavated examples, including that from Guiting Power 1 round barrow.

The animal corpses used throughout the programme were adult sheep. Despite obvious qualitative anatomical differences such an animal substitute was sufficiently human-like in combustability, being quantitatively similar in bone to meat to fat ratio, after surgical modification to remove the rumen with its considerable mass of semi-digested vegetation. Sheep corpses were further modified to allow closer correspondence with a human skeleton by cutting relevant tendons to allow fore- and hind-limbs to be laid flat, fore-limbs by the side, and hind-limbs extended. Attempts were in fact made to obtain primate corpses from zoos, but these were too unpredictably obtainable, and anyway subject to stringent post mortem quarantine because of latent transmissible diseases. Experimental cremation using a monkey corpse have however been carried out by Piontek 1976.

Although other configurations are possible, placement of the corpse prone in the uppermost part of the pyre seemed a practical, and simple option for first analysis, allowing display of the body and any associated pyre-goods to be followed by efficient cremation in the hottest, most oxidative zone of the fire. Preliminaries to the experiments -geophysical survey Since the burnt features resulting from firings were to be mapped, and in some cases monitored as buried magnetic anomalies, it was essential to locate experimental pyres in areas with a magnetic background as low and even as possible, without complication by existing archaeological features or presence of ferrous debris. Magnetic gradiometry, and magnetic susceptibility (MS) survey using a Bartington MS2 meter with D-head, over areas stripped of topsoil before construction of pyres, allowed positioning of experimental areas on natural clay relatively free from extraneous anomalies.

Objectives The experimental pyres were constructed and fired to provide information on the following topics, relating primarily to what is defined here as a 'unit box-pyre', a pyre of box-like construction, containing sufficient timber to cremate a single adult corpse with high efficiency (FIGS 2, 3, 5): -size, and structure required for an efficient pyre; -behaviour of pyre, corpse, and added pyre-goods during the period of combustion and cooling; -amount and distribution of overlying residual, and surrounding deflated and scattered pyre-debris to be expected from firing under defined environmental conditions;

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experimental pyres acted to retain the innermost load of generally smaller fuel-wood. Each pyre was framed and packed so as to allow free circulation of air, thus ensuring efficient combustion, whilst providing robust support for the corpse during the initial states of cremation. This promoted orderly inward collapse during the final reduction of the pyre, with effective retention of burnt bone in the resultant bed of char. The load of fuel-wood was graded from shavings and twigs concentrated around the ignition-point and into the core of the pyre, to larger timber forming the main outer bulk, in order to ensure a smooth sequence of combustion, which was obtained in practice from a single match.

-preparation of the ground Each experimental pyre was carried out at the centre of a 10m square area, stripped of turf by JCB to expose the same type of natural clay on which burning had occurred at the round barrows Guiting Power 1 and 3, hence enabling direct comparisons to be made. -positioning the pyre Experimental pyres were oriented so as to lie end-on into the prevailing wind, with the ignition point up-wind. Since construction and photo-recording of a pyre which contained full instrumentation took two days to complete, the direction for its orientation, fixed once the initial basal layer of the pyre was laid, had to be determined from predictions of wind direction and intensity obtained from the UK Weather Centre, Bracknell. These forecasts proved to be extremely accurate, and enabled pyres to be fired under ideal conditions of dry weather and light axial wind. For pyre 1 the wind direction was predicted as light and WNW'ly, with weather conditions dry and fair. For pyre 2 the weather was again correctly forecast as dry with broken cloud, wind light and variable but mainly W-SW.

The type of timber used for the pyre was based on that seen amongst the mix of charcoals in primary pyre-debris from archaeological contexts. Oak and ash, a year after cutting, were the main constituents, supplemented by less seasoned hawthorn, hazel, sycamore, dried grass and plant-stems. -Pyre 1: box-pyre of framed-stack type (FIGS 2-4,7,8,12; PLATES 1, 4, 6) This pyre was formed by repeatedly placing alternate pairs of timber beams, to form first one course of the side then one of the end, until a box-like shell, about 2m long by 1.5m wide and 1.4m high had been constructed. A shallow pit was dug at the windward end, providing an under-hearth, to aid ignition.

It was important for effective firing of these experimental pyres under optimal conditions, that ignition took place at the up-wind end, and then spread into the remaining pyre, to result in highly efficient combustion and a generally inward collapse of the burning pyre around the cremating corpse. Had pyres been fired under a cross-wind, or with the wind blowing back towards the ignition zone, then partial burning of the fuel-load could have caused premature collapse of the pyre and displacement of the corpse, with under-exposure to central heat of thermocouples placed within the pyre. The aim of the initial experiments was to run the pyre under supportive weather conditions, and a suitable windward alignment helped to ensure this. Although many prehistoric pyres, nor in fact certain of their modern experimental counterparts, did not enjoy such a clear run during combustion, as many samples of poorly cremated bone suggest, establishment of optimal experimental firings provides a standard against which to gauge such inefficiency.

Timbers forming this shell were fairly squared in section, and were mainly well-seasoned oak beams, their regularity increasing the stability of the pyre, thereby deliberately simplifying one unknown element for this pilot experiment, and allowing concentration on successful instrumentation. Oak beams were cut to 2.1m for sides, and 1.5m for ends. For the fresh-cut timber of the bier, two hawthorn side-stretchers, 2m long and about 8cm in diameter, were linked by ten sycamore cross-pieces, each about 4cm in diameter and 1m long, to provide support for the corpse. The shell of the pyre was constructed to enclose thermocouples on vertical metal pods fixed in the ground, and the central void was then filled with fuel-wood. This fuel-load consisted of smaller mixed wood (oak, ash, and some pine) graded in size so that the fire would spread rapidly into the interior, and then burn outward to consume the entire pyre. This avoided partial and asymmetric burning, possibly resulting in collapse of the pyre and displacement of the corpse. The entire structure contained 888kg of timber, about 60% oak, 25% ash, and 15% of other species. The shell of the pyre was sufficiently robust at the top to support the corpse firmly on its bier without the need for further timbering.

There is also evidence from many round barrows elsewhere in southern Britain that pyres may have tended to lie with long axis roughly E-W, perhaps to take advantage of prevailing westerlies, a situation also perhaps evident at Guiting Power 1 round barrow (FIGS 16-22). Materials used in construction Pyres 1 and 2 each contained about a tonne of wood, and comprised a stacked, box-like shell (pyre 1), or less formal interlace of larger timber (pyre 2), which

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experimental pyres frame at its corners, and to restrain the charring corpse from descending until the main pyre was well alight. The entire structure contained 956kg of timber, about 90% ash, with the rest as other local timber, including oak and pine. The frame of the pyre was constructed from limbs of ash, generally greater than 15cm in diameter.

-Pyre 2: box-pyre of framed-type (FIGS 2,5,6,7,9,12; PLATES 3a-f, 5, 7) This pyre was of comparable general construction to the first, and was monitored in a similar way, but differed from it in certain structural details. Whereas the shell of pyre 1 was constructed from regularly-shaped timber, that of pyre 2 was constructed from natural, and hence far less regular tree limbs, in order to approximate more closely a likely prehistoric structure. The interlocking shell of pyre 2 was still box-like, providing a stable retainer for the internal fuel-load and support for the corpse, but being less regular was in reduced contact with the ground, since the basal course was raised on natural angles in the wood. The degree of such ground-contact was considered likely to affect the pattern of burning caused by the pyre, with a reduction in radiant baking at the margins expected.

An experimental box-pyre of cross-stacked timbers raised on larger basal edge-logs, with the corpse on bier at the top, very similar to that of pyre 2 is illustrated in Duffy and MacGregor (2008), fig. 2, with no further details given. During all pyre experiments, except those deliberately compromised, intense radiant heat prevented any approach to the pyres closer than about 3 metres at full burn. This rendered further tending impossible, indicating that such care in initial structuring of the pyre and placement of corpse was critical for effective, orderly, and dignified cremation.

The first parts of the pyre-structure to be established were four sharpened, upright posts, hammered further into guide post-holes, and supporting a timber platform on which the corpse was to be placed. There is scattered evidence for 4-post structures in, and near pyre-sites under round barrows (FIG 15), and display of the corpse on such a platform prior to firing would seem at least possible. This four-post structure which was included with pyre 2 also gave a firmer support for the corpse than the shell could have provided alone, and helped further to retain the interlocked fuel-load, and reduce inherent risk of collapse. Introduction of ground-penetrating posts into the pyre-site also enabled the traces left by such burnt structures within the pyre-base to be examined, and compared against known archaeological data.

Of course the term 'dignified cremation' is entirely value-laden since it presupposes that undue exposure and re-handling of the corpse, for instance after slippage from the pyre in partly burnt condition, would be socially or ritually unacceptable. The only dignified cremation in modern Europe would be one in which the central stages were carried out entirely privately. This contrasts completely with current, equally accepted practices in northern India and Nepal for instance where cremation is deliberately public, and where often incompletely cremated bodies are committed to the river (PLATE 8a,b). -Pyre 3: box-pyre of log-edged type (FIGS 2, 10) Two oak logs, 2m long and 35cm in diameter, placed 1m apart, were infilled with a 573kg fuel-load of oak and ash to a height of 1m, with smaller wood near the firing-end to aid combustion. The corpse was placed directly on the fuel-load.

Instrumentation was then added under the 4-post platform: thermocouples were secured to upright metal pods fixed in the ground, with vulnerable cabling leading out to recording devices buried 20cm deep in a slit-trench until well beyond the radiation zone. The first tier of the pyre was then laid at the base of the 4-post platform, by placing a long timber at each side, and a shorter one at each end. This base-course was then infilled with parallel timbers, lying on the ground along the long axis to form a rough grate, aiding up-draught. Alternate long, and short timbers were laid at sides and ends to form the rest of the shell, infilling the centre with smaller timbers and blocks. About a third of the way up kindling was added at the front SW end, to encourage the rapid spread of fire into the central core, thus promoting symmetrical burning.

-Pyre 4: box-pyre of simple stack type (FIGS 2, 10) An unstructured 394kg stack of oak and ash timber, about 1.2m long, 80cm wide, and 70cm high, held the corpse, placed within its upper level. -Pyre 5: ring-pyre (FIGS 11, 12) A cone of stacked timber, 1,726kg in total, 4m in diameter, and 3m high at the apex, of mixed oak and ash, held the corpse within the mid-upper levels. Instrumentation placed within the pyres -measurement of temperature Temperature during firing was measured at key points within the pyre, in the underlying ground surface, also on and inside the corpse. Cable-mounted thermocouples (nickel-chromium type), capable of withstanding temperatures of about 1000oC, were wired to upright steel tubes, these

The 4-post structure supporting the corpse was of relatively green hawthorn: the 8 cm diameter uprights, each set 30cm into the ground, supported side-runners and cross-pieces, to form a platform 1.8m long, 1m wide and 1.36m high. Such fresh wood, for which combustion would be delayed, was used in order to help maintain the integrity of the

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experimental pyres latter hammered into the ground at the front, side, and rear of the pyre. This positioned the temperature-reading tips of thermocouples in the upper, mid, and lower pyre at 1m, 60cm, and 20cm above ground level. Thermocouple tips were also inserted at 2cm and 5cm depth within the ground surface, and placed on, and deeply within the corpse. Thermocouples were connected to remote recording units by buried cables, and data were logged at 5 minute intervals throughout experiments.

Preparation and placement of the corpse For pyre 1, the prepared corpse was that of a 4 year old Scotch half-bred ewe 65kg (144lb/10stone 4lb) in weight with the rumen removed, and 1.65m long when laid out with hind-limbs stretched out. In pyre 2, a 4yr old Scotch half-bred ewe was cremated, 70.3kg (155lb/11stone 1lb) in weight before removal of the rumen, and 1.55m long when laid out with hind-limbs stretched. Accompanying the adult was the unmodified corpse of a 1 day old Vendeen-cross lamb 2.5kg (5.5lb) in weight, 30cm in length, which had been held in deep freeze for 3 months after its springtime death, before thawing for the experiment.

Thermocouples could have been inserted into the pyre without securing to metal pods, and allowed to move freely as the pyre burnt, but with the danger of becoming inappropriately displaced. This option was rejected in favour of temperature monitoring at fixed points of known location in relation to the changing size and structure of the burning pyre. Readings could be discontinued, and thermocouples repositioned, if seen to be no longer relevant, as for instance from positions which became perched above the cooling ash-bed. Spot readings could also be taken, with the proviso that, at maximum burn radiant heat would prevent any approach to the pyre closer than about 3m.

Corpses used for the other experiments were similar to that for pyre 1. Each corpse was completely wrapped, and lashed securely, along with any primary pyre-goods placed on the body, within the woollen blanket used as a shroud-substitute. Placement of pyre-goods For certain pyres, including pyres 1 and 2 outlined in more detail here, samples of bronze and iron were placed on the corpse as primary pyre-goods, and were also secured to the pods supporting thermocouples, as satellite pyre-goods. Animal bone, and pottery of prehistoric type was also included to assess survivability.

The following thermocouples were set up: -in pyre 1: upper level at the centre; mid level at the centre, front, side and rear; lower level at the centre; in the ground at the front and rear; and in the body cavity of the corpse.

Other preliminaries Each pyre was fully constructed and instrumentation tested on the day previous to the firing, to allow a full day for the actual cremation to take place (PLATE 1). Immediately before the cremation was started, the tarpaulin keeping the timber dry was removed from the pyre, and the corpse placed in position. Temperature recorders were connected to thermocouples, re-tested, and the weather station switched on.

-in pyre 2: upper level at the front and rear; mid level at the front and rear; lower level at the front; in the ground at the rear; within and on the corpse. -gas analysis The composition of gases (oxygen, carbon monoxide, and carbon dioxide) within pyre 1 was monitored at intervals by hand-held meter, after extraction of samples down an elongate probe, pushed into the burning pyre-structure, approached with great difficulty at full burn. This established the extent of aerobic conditions within the burning pyre and the resultant ash-bed, useful for instance in assessing degradation of metal pyre-goods.

DETAILED EXPERIMENTAL RESULTS: pyres 1 and 2 (FIGS 3-9,12) Detailed results are only presented for these two pyres, as being typical of the full range of experiments. Where relevant, other experiments are discussed when any departures from these standards occur.

Recording the weather Environmental conditions were monitored next to the pyre, using an automatic portable weather station: wind speed and direction, air temperature and humidity were logged every 5 minutes (FIGS 4, 6; PLATE 1c).

Summary of cremations Fine, dry weather prevailed for the week preceding and the days during and after each experiment (pyre 1: 6th July 1993; pyre 2: 3rd July 1994). Timber structures were therefore dry, ensuring cremation and processing of pyre-debris under ideal conditions. Windward place ment of the combustion-points of pyres, provision of a sturdy retaining frame, and

Recording of events Each pyre was recorded photographically, and by written record, at key points throughout construction, firing, cooling, and clearance of its ash-bed.

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experimental pyres internal grading of the fuel-load, all ensured a highly efficient cremation, which gradually drew the burning corpse into the pyre by structured inward collapse of timbering. Once lit, temperatures within the pyres rose rapidly within half an hour to about 1000oC, and within 2 hours each pyre was reduced to a low ash-bed.

-char-bed After about an hour, the timber framing forming the sides of both pyres had burnt away sufficiently to cause them to collapse inwards, over the reduced remains of the corpse, by now well down towards the base, and covered with burning char. After another two hours the pyre had reduced to an ash-bed, admixed with glowing fragments of timber, at about 500oC centrally, with ground temperatures at about 300oC.

Stages of cremation The entire process of cremation, similar for pyres 1 and 2, can be divided into four main stages (FIG 13; PLATES 3a-f):

-cooled ash-bed After 3 hours from ignition, most of the remaining charred timber had converted to ash, and internal temperatures were low enough for clearance of debris and safe retrieval of cremated bone by hand (PLATE 7).

-initial firing Each pyre was constructed with a sheltered port at the base of the windward end, containing the light and easily-ignitable wood used to start the pyre burning. Placed behind this kindling was a cone of slightly larger wood, which carried the fire inwards and upwards to cause an evenly expanding central area of combustion, thus starting the main burn. The light, prevailing, axial wind was sufficient to cause a rapidly spreading blaze.

For each pyre, the intensity of burning reduced over a tonne of timber to a few kilograms of ashy residue, the majority being converted to gas and ash, both readily removed from the site by an ascending plume, carried away under light wind.

-main burn Within about 30 minutes of ignition, the fire had spread through the central fuel-load, to cause marked surface-burning of the main timbers and corpse. The essential shell-structure of both pyres remained intact however, with the corpse beginning to sink deeper into the pyre as the light timber support disintegrated, and the burning fuel-load settled. Temperatures in the upper pyre reached 1000oC, with those elsewhere remaining lower, at 500-800oC. The ground surface was heating up sufficiently to cause the magnetic enhancement of sediments later measured.

Left untended, such experimental box pyres, if properly structured, undergo automatic internal collapse and result in completeness of combustion, leaving only a few of the larger timbers smouldering around the margins of the ash-bed. Trials with log-edged box-pyres (FIGS 2, 10) also left such charred lateral timbers. Some of the larger charred logs from certain pyre-sites under round barrows (TABLE 5) can perhaps be interpreted as remnants of major timbers framing the base of a pyre:

TABLE 5: Examples of larger charred timbers surviving at round barrow sites Barrow Canford Heath Amesbury G71 Brenig 45 42 40

timber: length (m) 1.2 0.5 3.8 1.4 0.7 0.8

ref. Ashbee 1954 Christie 1967 Lynch et al. 1974

involve conditions of forced ventilation.

-pits containing hot pyre-clearance debris For pyre 1, two small pits, about 35cm square and deep, were infilled with glowing pyre-debris, then capped with turf, to determine any soil changes accompanying such separate disposal of pyre material. Changing temperature was logged by thermocouple over a 5 hour period. Such pits have been noted at certain round barrows (Gibson 1986, 1993), including Guiting Power 3 (Marshall 2007b). Very little burning or magnetic enhancement occurred over the sides and bottom of pits, suggesting that production of any such marks would

Details of the cremation process -pyre 1 (FIGS 3,4,7,8,12; PLATES 1,2,4,6) ..summary: Burning spread rapidly from the ignition-point at the base of the frontal, windward end to envelop the entire upper half of the fuel-load, allowing the corpse to sink within the less burnt frame as fuel burnt away. The upper half of the frame then burnt away, most timber falling inwards to join the main fuel-load, the lower levels of the frame eventually collapsing over the char-bed, the upper

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experimental pyres three side-tiers up from the base, and lay more in reducing than in oxidising conditions. On the E, originally the 'head' end of the pyre, the top tier had collapsed at the S side, which was where most of the flame was concentrated at this stage. Compact burning wood, char, and ash, at the base of the pyre, gave reducing conditions and great heat, with much of the debris glowing red. A few of the upper fragments of burning wood had dropped down and rolled away from the pyre. The corpse had tilted sideways slightly, possibly aided by sinking onto the upright metal pods holding thermocouples, but still retained its overall position three end tiers up from the base. The corpse appeared well burnt within the carbonised residues of its blanket-shroud, with some bone protruding out of the charred centre, and fully oxidised distal femora clearly visible.

levels of which contained the cremated remains of the corpse. Within 3 hours the pyre had burnt to a low ash-bed, largely within its original confines, but with some lateral scattering of burnt debris. Failure by burn-out of certain of the thermocouples towards the end of the cremation indicates the intensity of heat they encountered, with temperatures exceeding 1000o. ..time course: The cremation was carried out on 6th July 1993. +0min (0955h GMT): The pyre was lit at the base of the front, windward end within the small hearth-scrape provided. +5min: Flame took hold rapidly and reached the level of the corpse. A temporary NW wind resulted in increased burning on the opposite side but caused no structural problems.

+1h 10min: A few other charred timbers dropped away from the western, 'foot' end of the pyre and rolled to the side. The fore-leg of the corpse was now protruding, and the process of tilting was seen to have continued. All metal samples secured to pods remained in position.

+15min: Internal burning became extremely fierce under a temporary change of wind direction, but which soon veered back onto axis, ensuring more even burning. The central fuel-wood was still in place and burning well. The corpse was well charred and slightly slumped as the bier started to burn away, but it remained at its original level on the platform. All logs were now charring, except for the base-level on the ground. Radiant heat was now very intense, even up-wind and 6m away, making any closer unprotected approach, as for tending, impossible.

+1h 15min: The fifth tier at the eastern, 'head' end had fallen inside the remaining structure, and at the W end had become detached and then rolled away from the pyre in charred condition. Both side-tiers still had five levels, but the SE corner had collapsed slightly to a lower level. +1h 17min: Collapse continued, as the third and fourth tiers at the E end burnt away towards the SE corner. The corpse now rested at the second tier up, and was still burning well.

+25min: The structure was still intact, but the bier had given way and the corpse had slipped down to about half the height of the original pyre.

+1h 20min: On the S side, the fifth tier rolled off and to the side because one of the lower courses had collapsed, resulting in local instability. At the eastern, 'head' end, only the second tier remained intact; the first had broken half way along, the third had burnt away, and the fourth had collapsed inwards.

+35min: The contents of the upper three tiers had now burnt away, leaving them empty, the body now lying half way down inside the pyre, with one tier of the shell above it, supported by fuel-wood still in place. The lower leg-bones of the still articulated corpse were exposed and well oxidised. The corners of the pyre remained intact, and with the lower tiers of logs secure, even relatively unburnt in places.

+1h 22min: The upper half of the charred pyre shifted slightly to the S, leaving only first to third side-tiers in place, the fourth and fifth having dropped off. The interior of the pyre was still burning well, obscuring the corpse, as viewed from the E end.

+50min: The basic frame of the pyre remained intact, although it was all burning steadily. The remains of the bier supporting the corpse had burnt away completely, and the body had sunk onto the remaining fuel-wood, three tiers up. The top tier had collapsed slightly at the S end, where the wind direction had concentrated initial combustion. Denser layers of burning wood at the base of the pyre created anoxic, reducing conditions. Great heat prevented any approach to the pyre closer than about 4m.

+1h 25min: All of the timbers were heavily burnt, but four of the six original courses were still standing at the rear end and right side, with the other two sides more collapsed, but still retained enough structure to hold the lowest fuel-load. Fallen burnt wood lay scattered around the margins of the pyre. The upper, and mid level thermocouples were exposed on their metal pods above the burning pyre.

The corpse had sunk onto burning wood only two or

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experimental pyres remained in the area of thorax and stomach, with some ribs and a few vertebrae still only charred. The two lowest side-logs were still burning, as was some of the central wood, but by now the pyre was reduced to a mound, about 30cm high, consisting mainly of very fine wood ash and fragmented charcoal. A stronger wind, gusting to about 3.5 m/second, was dispersing much of this finer ash. Around the ash-bed, fallen logs had left a clear impression over the clay surface, as red scorching with a black surround. The axial and lower limb areas of the corpse were over on the N side of the ash-bed, with the skull to the SE, possibly displaced by the central instrument pods.

Charred tissue and highly burnt bone from the corpse lay over the glowing fuel-load. +1h 28min: Further collapse of the pyre-sides occurred at the S corner of the W end. +1h 42min: The structure had now largely collapsed in a controlled manner into a heap of ash, not extending far beyond the original confines of the pyre. At the 'foot' end, the SW corner had collapsed down to the lowest level, the NW corner still had three end- and side-tiers, charred but intact, although the stacking had collapsed along most of the circuit. A single bone joint from the corpse had fallen out at the W end, and lay 1m beyond the pyre, possibly knocked out by falling timber. The oxidised pelvic bones and spine of the corpse were visible towards the NW corner, and much of the generalised bone had been well oxidised and shattered, lying mainly over the central part of the ash-bed along its mid-line.

+6h 35min: The pyre was now almost burnt out, with only two lowest side-timbers still burning in broken 30-40cm lengths, one on the NW corner, the other on the SE, with other marginal areas now almost cool enough to handle. The remains of the corpse were not still burning, with bone and soft tissue residues seen to be lying over the ash-bed in approximate anatomical correspondence with the original placement of the corpse.

+1h 55min: Most of the structure had burnt down to one or two layers, and all timbers had collapsed inwards, except at the NW corner where four crossed logs remained.

+7h 35min: A few kilograms of hot char were removed for placement in a separate pit, further to interpret the remains of such pyre clearance deposits which sometimes accompany prehistoric cremation. The char-bed remained quiet and unburning, with fine ash being blown across and away from the site.

+2h 5min: The NW corner was now reduced to three crossed logs, which lay well down. The interior of the pyre was now at a higher level than its margins, as a result of accumulating ash. The remains of the corpse were visible, with much fragmented, well oxidised bone exposed. The thorax and abdominal area still remained as a black charred mass, with spongy tissue-residues surviving.

+9h 5min: The ash, except for that on the periphery of the bed away from the corpse, was still too hot to handle, and so the entire ash-bed was allowed to cool further overnight before any clearance was attempted.

+2h 12min: Although well burnt down, the pyre was still hot, and could only be approached to within about 2m.

+23 h: The ash-bed was cleared. Over-night there had been further winnowing by wind of finer wood ash, and its depth along the centre line was about 6cm at the E end, and 1.5cm at the W end, but with an additional 5cm depth in the small depression forming the under-hearth. Almost a tonne of timber had, therefore, been reduced to a few kilograms of ashy residue with inclusions of char.

+2h 20min: The skull lay exposed at the E end of the char-bed, rolled over, and away from the atlas vertebrae, its vault remaining whole, with some charred soft tissues remaining attached to its base. The upper limb was visible, with the axial body still charred and burning. +2h 25min: Larger masses of soft tissue from the central body cavity were still slowly cremating to form spongy black residues. By now the fiercer burning had died down, with little visible flame coming from thicker char deposits, but with many of the remaining logs still glowing.

Metal pods and thermocouples, with any suspended metal samples, were carefully pulled out. Distributions of bone and fallen pyre-goods were plotted. The more obvious, and vulnerable bone, soft tissue residues, and pyre-goods were carefully removed, leaving the remaining thin ash-bed over the burnt clay surface covered with tarpaulin overnight, before further clearance, recording, then excavation took place (FIGS 7,8,12; PLATES 4, 6).

+3h 15min: The pyre was well burnt down to form a mound of smouldering ash and char. The skull had split open, and some soft tissues still remained in the area of the thorax, but were well burnt.

-pyre 2 (FIGS 5,6,7,9,12; PLATES 3,5,7) The cremation was carried out on 3rd July 1994. ..summary: The course of cremation was similar in

+4h 45min: The corpse appeared to have stopped burning, but considerable charred soft tissue

23

experimental pyres collapse starting. The corpse was still in place on the charring bier.

timing and general characteristics to that of pyre 1. Combustion started at the front, windward end, then spread towards the rear of the pyre under light wind, and upward under rising heat to consume the upper area of the pyre. The zone of intense initial burning tapered up from the completely burning front-end to restricted burning at the top of the back-end. Burning then spread from this wedge to consume the basal part of the pyre and the back end, with progressive inward collapse of timbers forming the frame, the corpse descending within the frame as the burning fuel-load sank. The pyre was completely reduced within 3 hours to a low ash-bed, in the top of which was admixed the highly cremated bone and tissue residues from the corpse. Residual pyre-debris was mainly confined to the area of the original pyre, with some lateral scattering out to about 1m, and was sufficiently cool to be handled with care within about 8 hours after ignition (PLATE 7).

+40min: Burning at the base of the upper wedge of the pyre now spread downwards to include fuel in the lower tiers and further towards the back which, although charred, was the most intact part of the frame. The upper half of the frame was now completely burnt away at the front, leaving only the bottom two tiers in place, with a displaced log from the third tier overlying. The upper sides of the frame were burnt away, with the remaining charred lower side-timbers sloping down from the less burnt back. The fuel-load was reduced to an intensely burning bed in the lower half of the pyre, on which the corpse now lay, well blackened, with most shroud residues gone. The uprights and side runners of the bier-platform were smouldering but intact, held from rapid combustion by their greener wood, but the cross-pieces on which the corpse was first placed had burnt out, except one at the back, thereby allowing the corpse to sink within the frame. Charred wood lay scattered around the margins of the pyre within 1m, and was visibly scorching the ground.

Careful structuring of this pyre allowed display, followed by efficient cremation of the corpse, without any further intervention. The burning pyre collapsed in an ordered way: the base of the bier burnt out, allowing the corpse to sink onto the depleting, intensely burning fuel-load within the frame, which itself gradually collapsed inwards to help cover and consume the corpse. The interlocking structure of the timber frame prevented any disorderly collapse and, despite the early combustion of the front end, the surviving structure remained standing, to fall inwards. Delayed burning of greener timber, deliberately used for the uprights of the platform acted, as intended, to support the back-corners of the pyre until the final stages. The general design of this pyre was based on insights gained from the behaviour of the more regular, massive, and less naturalistic pyre 1, where similarly ordered burning was achieved.

+50min: The upper half of pyre had now burnt away, except for the uprights of the platform, but one side runner from the bier had collapsed, and the other was sagging. Burning had spread to the base of the frame at the sides, and into the mid-lower back, which was still largely standing. The corpse, well burnt but still intact, was sinking within the surviving basal frame, and was well ablaze, as the remaining wet body-tissue dried towards combustibility. +1h: The basal two to three courses were now heavily burnt and starting to collapse, with the surviving lower part of the back-end still the most intact. Much of the more massive timber forming the basal tier was still unburnt, with some of the cross-pieces forming the basal grate-layer still intact. Three uprights of the platform were still standing, but one at the front had fallen, burnt through at the base as the side timbers were consumed. The corpse was reduced to a mass of charred tissue, with oxidised bone protruding. The upper half of the pods bearing thermocouples were now exposed above the burning mass.

..time course: +0min (1000h GMT): The pyre was lit at the base of its windward end. +10min: Flame spread upwards and inwards from the ignition-point to consume the upper wedge of the pyre, tapering from the entirely blazing front to the unburnt back end. The top surface was burning intensely, with the corpse charring well. +20min: Burning was still confined to the upper wedge of the fuel-load but had intensified, and the corpse was well alight with burnt lower limbs protruding from the charred shroud.

+1h 20min: The lower sides and back of the pyre were now heavily burnt, but with the cores of their smouldering timbers still held in place by the remaining mass of fuel, glowing at red heat. Only the two uprights at the rear of the platform were still standing. The corpse was visible as a mass of carbonised soft-tissue, perched on the fuel-load, with a scatter of well-oxidised bone on and in its ashy surface. Further burning logs lay fallen at various points around the margins of the pyre.

+30min: The frame and fuel-load were now largely consumed within the upper wedge of the pyre, leaving much of the remaining mid to upper frame empty, with logs charred away, and slight inward

24

experimental pyres +1h 45min: All sides of the pyre were now fully collapsed onto the glowing ash-bed, which was about 40cm high at most. Basal logs were still only partially burnt. The two uprights at the back of the platform were still standing. Metal instrument pods now stood well above the burning fuel, exposing thermocouples at the upper and mid levels. The corpse showed a reduction in blackened tissue and bone was sinking further into the ash-bed.

..details for thermocouple locations ...in the ground: ....at the front (Gf): A rapid rise to 700oC occurred after 30 minutes, remaining between 600 and 700oC until 2 hours, then cooling to 300oC after 3 hours, and to 100oC after 7 hours. ....at the rear (Gr): A rapid rise to 960oC took place within 10 minutes, then a steady decrease to 100oC after 3 hours, thereafter cooling further to 30oC after 6 hours.

+5h 10min: All timber, including the surviving rear uprights of the platform, had now smouldered away, leaving parts of the more massive basal course in semi-burnt condition. The ash-bed was about 30cm deep and covered the original pyre area, but with some surrounding scatter spread out to about a metre. The corpse had been reduced to a scatter of black tissue residues and white oxidised bone, some relatively intact but much fragmentary, within the uppermost ash-bed and lying in approximate correspondence to the original corpse.

...pyre at the upper level ....at the centre (Cu): A rapid increase to 760oC occurred after 15 minutes, with a plateau between 700 and 1000oC until 3 hours, this dropping to 800oC at 4 hours, at which point the thermocouple failed. ...pyre at the mid level ....at the centre (Cm): A rapid rise to 850oC took place after 10 minutes, with a plateau between 700 and 800oC until 2 hours 30 minutes, thereafter decreasing to 200oC after 4 hours, and to 80oC after 6 hours. ....at the side (Sm): Temperatures rose to 1060oC after 20 minutes, with a plateau at about 1000oC until 1 hour, then rapidly decreasing to 200oC after 2 hours, and to 60oC after 4 hours. ....at the front: Low results indicate failure of the thermocouple, possibly through initial exposure to extreme temperatures greater than 1000 oC. ....at the rear (Rm): Temperatures rose steady to 1000oC after 1 hour, thereafter cooling with intermittent peaks to 300oC after 4 hours, and to 80oC after 6 hours.

+7h: Part of the hot ash-bed was cooled with a water-can to determine whether this was a viable process for retrieval of bone, but was abandoned when it was found to cause clogging, and to hinder collection. The remainder of the ash-bed was far more satisfactorily screened for cremated bone by raking whilst it remained in dry condition, which may well, therefore, have been the ancient practice. Similar problems in extracting bone from wet ash were encountered by Henricksen (pers. comm.), who achieved good retrieval after hand picking of bone combined with winnowing remaining ash away. After recording, sorting, and clearance of the ash-bed, the metal pods holding thermocouples were removed, the burnt surface carefully cleaned by very light brushing, and then the area was covered by tarpaulin, pending further recording and sampling. Considerable care was required to avoid disrupting the thin, friable surface, which bore clear signs of differential burning (PLATE 5). The cleared pyre-base was planned, its magnetic properties determined, and samples taken.

...pyre at the lower level ....at the centre (Cl): An irregular rise to 800oC occurred after 1 hour, then a steady decrease to 220oC after 2 hours, and to 40oC after 5 hours. This thermocouple, now well above the burning fuel, was then transferred to read temperatures within the ash-bed. ...associated with the body ....on the surface (Bo): A rapid rise to 1040oC took place after 30 minutes, followed by a steady decline to 180oC after 2 hours, and to 50oC after 6 hours as the thermocouple became detached. ....in the viscera (Bi) Temperatures rose to 700oC within an hour, less than those recorded just outside the corpse, and then declined to about 300oC after 3 hours during advanced cremation on the subsiding pyre.

The residual char and ash bagged for further screening contained one item of bronze, and 19g of cremated bone, which suggests that such semi-cleared pyre sites under barrows may be marked by small quantities of characteristic debris left after routine retrieval of human remains. Changing temperatures within the pyres -pyre 1 (FIG 4) ..summary: Temperatures within the upper pyre rose to over 1000oC within 20 minutes, remaining at this level for about an hour. Temperatures within the lower pyre rose less rapidly and to a lower maximum of 800oC within the same period.

..pits containing hot pyre-clearance debris The contents of the first pit cooled steadily from an initial 560oC to 80oC after 2 hours. The interior of the second pit cooled from 420oC to 180oC over a

25

experimental pyres the thermocouple failed. ....in the viscera (Bi): Temperature climbed to 600oC after 40 minutes, varying between 300 and 500oC until 2 hours 50 minutes, as organs burst and quenched the tip.

similar period. -pyre 2 (FIG 6) ..summary: Temperatures within the upper pyre rose to over 1000oC within 20 minutes, remaining at this level for about an hour. Temperatures within the lower pyre rose less rapidly, to a lower maximum of 800oC within the same period. Thereafter, the temperature of the burnt-out pyre fell to about 20oC after 8 hours.

Other data (FIGS 4,6; PLATE 1) -wind During operation of pyre 1, the wind gusted up to 4 m/second, coming mainly from the WNW (050-150 degrees from Grid North). During pyre 2, the wind, at speeds of 0-3m/second, was from the SW sector during the first 4 hours, then backing to the S for the remainder of the period.

..details for thermocouple locations ...in the ground ....at the front (Gf): Temperatures rose to about 70oC within 45 minutes, remaining at this level until 8 hours. ....at the rear (Gr): Temperatures rose to about 80oC within 2 hours, remaining thus until 8 hours.

-gas analysis During pyre 1 hand-held sampling was difficult because radiant heat prevented any close, sustained approach to the pyre, but was nevertheless carried out. Results satisfactorily showed that within the fairly intact pyre conditions were strongly reducing until collapse of the frame occurred, when oxygen levels increased. Accumulation of dense ash at the base of the pyre then maintained reducing conditions within the ash-bed. Levels of carbon monoxide rose rapidly within the pyre to about 16,000 parts per million when the pyre was at its most intense.

...pyre at the upper level ....at the front (Fu): A rise to 940oC occurred within 30 minutes, thereafter dropping to 100oC after 2 hours 30 minutes, remaining at this level until the thermocouple failed after 5 hours. ....at the rear (Ru): A rise to 850oC occurred after 25 minutes, with a plateau between 800 and 900oC until 1 hour 15min, then dropping to 100oC after 3 hours, and to 20oC after 8 hours. ...pyre at the mid level ....at the front (Fm): A rise to 1050oC occurred after 35 minutes, cooling rapidly to 820oC after 45 minutes, when the thermocouple failed. ....at the rear (Rm): A rise to 940oC after 35 minutes climbed again steadily to 1070oC after 1 hour 5 minutes, dropping to 820oC after 1 hour 20 minutes, when the thermocouple failed.

Analysis of the pyre-base -visual (FIG 7; PLATES 4-6) After careful removal of remaining debris from the pyre-base, the burnt surface was lightly swept then photographed and planned whilst still in fresh condition. The pattern of burning over the clay surface under each pyre had a similar structure. A central area, which was less fire-hardened, more ashy, and generally blacker in appearance, lay under the pyre itself. Surrounding the margins of the burnt-out pyre was a ring of fire-reddened crust, well baked by radiant heat, but with less ingrained ash and finer charcoal. This more oxidised ring of baked sediment extended outwards over the surface for a distance equivalent to between a third and a half of the width of the pyre. This ring-feature was more pronounced for pyre 1, its more massive, upright, and calorific frame, with its regular base in closer contact with the ground, generating higher radiant heat than pyre 2 and other pyres which were of lighter and lower build.

...pyre at the lower level ....at the front (Fl): A rise to 860oC after 1 hour 5 minutes dropped away to 470oC after 1 hour 30 minutes, with a flare to 670oC peaking at 1 hour 10 minutes, temperatures climbing steadily again to 840oC after 5 hours 20 minutes, plunging rapidly to 60oC at 5 hours 30 minutes, after partial quenching during test retrieval of cremated bone. ....at the rear (Rl): A redundant thermocouple was moved from its original position in the corpse (Bi), after 3 hours 30 minutes, in order to monitor the cooling ash-bed. Temperature at this new location climbed steady from 100oC to 160oC after 5 hours 45 minutes, with a flare to 300oC after 6 hours, then dying back to 200oC after 6 hours 40 minutes.

-geophysical survey and sampling (FIGS 8,9,12) Two types of magnetic mapping were undertaken over burnt pyre-bases: ..magnetic gradiometry The exposed, burnt base of pyre 1 was mapped at 25cm intervals, using a Geoscan FM18 gradiometer to determine how useful such a technique might be in scanning excavated surfaces for traces of pyres or other burnt material. The more intensely magnetic

...associated with the body ....on the surface (Bo): Temperature of the probe remained low at 30oC for 20 minutes, locally shielded by the corpse from increasing heat, thereafter climbing rapidly to 860oC after 45 minutes, then dropping back to 450oC after 1 hour 30 minutes when

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experimental pyres ends of marginal wood to be consumed last (FIG 11). If the later, cooler stages of the firing are tended manually, when closer approach becomes possible, then such unburnt timber ends are often thrown onto the burning centre of the fire, still further reducing relative burning at the margins. The conical shape of a ring-pyre also markedly reduces radiant burning of sediment at the edges of the pyre-site, because fuel-wood is angled away from it.

outline of the pyre could be seen against lighter background anomalies, but not well enough to suggest routine use of the method for unsupported prospection. The crust of burning was thin, and the gradiometer was responding not just to the surface, but to deeper anomalies in the subsoil. ..magnetic susceptibility (MS) survey over exposed burnt surfaces Survey at 25cm intervals over the pyre-bases, using a Bartington MS2 meter, fitted with the type D head, allowed MS to be determined for the top few centimetres of the surface, restricting measurement more to the zone of induced change. The area of burning, both as seen visually and around the margins of the pyre, where no detectable colour change took place in sediment, could be accurately mapped using this equipment.

Such information on the observed relationship between pyre-site and pyre-base is useful in suggesting structural details of original pyres from their excavated pyre-bases at round barrows, as has been done at Guiting Power 1 (FIGS 3,5,7-9,19,22). Experimental data suggest that for box-pyres, the most common type of pyre likely for routine cremation, the length and width of the pyre-site occupy about 60% of the pyre-base, as mapped by magnetic susceptibility (MS). On this basis, and using the axis of the excavated pyre-base, the approximate size, shape, and orientation of the original box-pyre can be inferred. This can then be integrated with information from surviving residual pyre-debris as to the species and bole of timber used for the pyre, the number and maturity of individuals cremated, inclusion of any pyre- and grave-goods, the presence of single or repeat cremation, and the extent to which the ash-bed has been cleared or otherwise disturbed.

Characterisation of pyre-bases by visual means, and by mapping magnetic susceptibility (MS) over and within their surfaces, provides structural information on the original pyre-site, and allows pyres to be distinguished from any scatters of re-deposited pyre-debris. These latter overlie no characteristic pyre-base, and cause no burnt changes in adjacent sediment of the type which are only induced by far more intense, direct firing. In any discussion it is important to distinguish between the 'pyre-site', the basal limit of the unfired pyre, and the 'pyre-base', the patch of burning induced under it after firing (see 'Definition of terms'). The relationship between these two areas differs according to the type of pyre used, and the firing conditions.

In the case of pyres from archaeological contexts, mapping from MS is an essential supplement to the visual plan of any surviving ash-bed or spread of baked sediment as a basis for reconstruction. MS more readily survives the clearance to which such pyre-bases were usually subjected, penetrating deeper than the zone scraped away (FIGS 8,9). In the absence of a clear burial deposit, or characteristic residual material or items, certain localised firings, subject to such clearance, and which only survive as MS anomalies, may not even be registered as candidate pyres (FIG 17). It is therefore important to use the most robust data as a basis for discussion.

The burnt and magnetically-enhanced pyre-base which develops under the ash-bed, partly marked by reddening of sediment and further detectable instrumentally, is larger than the pyre-site for box-pyres of simple stack- and framed- types. In these cases radiant baking of sediment around the margins of a fierce pyre adds to this area (FIGS 8,9), and the collapse of the burning pyre tends to cause a lateral spread of char and ash beyond the original limits of the fuel-load (FIGS 3, 5).

..magnetic susceptibility (MS): profiling through exposed burnt surfaces (FIGS 8,9; PLATE 6) Although the depth of burning could be seen in excavated section as a shallow crust, it was essential to determine the true depth of burning as seen by increased MS. Continuous laboratory scans of MS through prepared cores showed that enhancement occurred within the top 3 to 8cm of sediment, and mainly within the upper half of this.

By contrast, for box-pyres of log-edged type the pyre-base is smaller than the pyre-site, the ash-bed being retained within the lateral logs, which rarely burn to completion, and hence shield the margins of the pyre-site, especially if they are substantial and of unseasoned wood (FIG 10). Lateral baking of surface sediment is prevented by the screening effect of these lateral logs, and is confined to the open, down-wind end, where enhancement can spread beyond the pyre-site. The pyre-base is also smaller than the pyre-site in ring-pyres, where the fire and the ash-bed developing within it become concentrated towards the centre, leaving the outer

..spot-sampling of magnetic susceptibility (MS) over exposed burnt surfaces Small spot-samples were taken from differently burnt areas within pyre-bases, for determination of MS. The most intensely burnt, reddened areas had susceptibilities from about 500 to 1200 (mass MS:

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experimental pyres units here x 10-8 SI), and the ashy interior had levels between 150 and 450, with control values for unburnt clay beyond the pyre-base at 40-50.

indeed burnt in place, as sometimes suggested, in order to have been carbonised at depth they would have needed fuller aerobic conditions, unlikely at the base of a burning pyre.

-long term monitoring of the buried pyre-base Whereas much of the base of pyre 1 was removed by excavation (PLATE 6), the base of pyre 2, intact except for very minor and localised sampling, was preserved by burial, as part of a long-term experiment to assess subsequent changes. After full recording and minimal sampling, this pyre-base was reburied under about 30cm of natural clay, then re-seeded to match surrounding pasture, to undergo continuing soil processes of a type which might be experienced under an earthen barrow mound of the type encountered at Guiting Power 1 and 3.

-assessing the degree of disturbance of pyre-bases found in archaeological contexts Comparisons between distribution of cremated bone within residual pyre-debris from archaeological contexts and that observed by experiment (FIG 14) might allow the degree of any disturbance sustained by an otherwise uncleared, ancient pyre-base to be gauged. Experimental determinations show that there is a fair degree of spatial correspondence between location of major skeletal markers in the unburnt corpse, and in the spread of cremated bone which accumulates over the ash-bed after cremation (FIGS 3,14). The corpse descends within the frame of the burning pyre, retaining some articulation until the closing stages of the main phase of combustion, thereafter breaking up more fully, until it reaches the ash-bed. Disarticulation of the corpse by burning, with displacement of bones and their fragments as they fall through the lattice of timbers remaining in the pyre, accounts for the fairly minimal horizontal spread of bone. Since the layer of cremated bone in the primary residual pyre-debris is relatively shallow, typically 10-15cm, no useful inferences are possible from vertical stratigraphy of bone. Any raking of the primary pyre-debris, to encourage final burning or to break up soft tissue residues might be detectable if it resulted in wholesale dispersal of cremated bone beyond the semi-articulation, and degree of anatomical correspondence expected from experiment. Such analysis would only be possible in cases where the usual wholesale retrieval of bone from the ancient ash-bed had not taken place.

-excavation (FIG 8; PLATE 6) The base of pyre 1 was fully recorded in plan then examined in section after removal of opposing quadrants by excavation. The visibly burnt crust was shown to be no thicker than 1cm, with most of the burnt sediment concentrated in the upper half of this zone. Despite the high temperatures generated within pyres, much of this heat is directed upwards, with the cooler mass of underlying soil and bedrock acting as a sink to draw heat from surface sediment and prevent deep penetration of burning. The thinness and fragility of pyre-bases clearly indicate that they would be vulnerable, after firing, to damage sustained during clearance of debris, trampling during mounding, cutting of pits for burial deposits, or exposure to the weather during any delay in barrow construction. Only vestigial traces of such features should perhaps be expected to be encountered during archaeological excavation, and in those cases where pyre-bases are well-preserved, rapid sealing must have been the case. This again stresses the need for full instrumental assessment of excavated surfaces under barrows, in order to identify candidate pyre-bases which have not survived visibly (FIG 17; Marshall 1998).

Analysis of artefacts and other material included within the pyre-structure The high temperatures generated within these experimental pyres, certainly over 1000oC and for limited periods up to 1200oC in parts of the fuel-load at full burn, caused destruction of all but the most resilient material. The following fairly predictable conclusions can be made regarding the behaviour of pyre-goods, considering materials in order of increasing survivability. Pottery of prehistoric type was completely granulated, beyond recognition or recovery. Organic residues, mainly the soft tissue of the corpse, became completely carbonised, much surviving as carbonaceous foam, which disintegrated easily when handled (PLATE 7). Bone, although highly oxidised, survived well, often in larger and anatomically-recognisable fragments, with less substantial adult bone and that of infants faring far less well. Bronze (PLATE 2; TABLES 6-10) was often completely melted, to disappear as tiny globules. Iron maintained its shape well, pyre temperatures rarely approaching its melting point, its inclusion here being mainly to monitor upper limits for

-survival of ground-penetrating timbers The bases of the four posts supporting the platform within pyre 2 survived the firing as charred stumps protruding above the ground-surface, and as unburnt wood below it. The mound of ash, which had shielded the ground under the pyre from the most intense radiant heat, had also helped to prevent complete aerobic combustion within the ash-bed. The ground also acted as an effective heat-sink, preventing deep burning of the wood. This indicates that such posts are likely to be marked in the archaeological record, not as charred stumps, but rather by pyre-debris filling their sockets as stumps are pulled out. Posts forming rectangular structures, perhaps acting to retain the fuel-load and support the corpse, are often closely associated with possible pyre-bases found under certain round barrows (FIG 15). If bases were

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experimental pyres Bronze Age as well (Henricksen: pers. comm.).

temperatures achieved in the pyre. Metallurgical analysis of both surviving bronze and of iron which went through the pyre show that crystalline changes occurred to indicate this re-heating, and that such surviving burnt pyre-goods might be recognisable as such on this basis. Flint withstood firing conditions very well, but with some splitting and general heat-cracking evident.

-copper and bronze The programme of experiments relates specifically to pyres associated with Bronze Age barrows, and so the only metal placed as primary or secondary pyre-goods was copper or bronze. Iron was included only to gauge upper temperatures achieved. Such metal items were placed on the pyre to determine how well they might survive cremation, and the effects on this of sample type, size, shape, location, and degree of mobility in the pyre. Metallurgical changes induced in the items by the pyre were also of interest, in terms of identifying them as pyre-, rather than grave-goods.

Pyre-goods from archaeological contexts can include surviving fragments of worked bone, antler, or items of copper and bronze, the latter metals often highly melted to small blobs, suggesting placement of items with the corpse or on the pyre. Cremated animal bone from these contexts suggests offerings of meat placed on the pyre, and that other less resilient organics, perhaps representing food-stuffs, may also have been present but have not survived. Surviving pyre-goods therefore, obviously, represent a minimum for what may have been present, with no survival to the end of cremation of anything less combustible than stone, flint, bone, and metal, with only vestiges of these remaining, and these with diagnostic, modified structure. Survival rates of items would be improved in pyres which operated at lower temperatures and at slower rates, or which experienced only partial burn-out, allowing items the chance to detach and fall to lower and less intensely heated locations.

The results from pyre 1 are typical of data from other pyres, and so are presented here in detail. Metal items were distributed on the corpse, within the body of the pyre, and on the ground. These items were divided into three placement groups, either free to fall within the pyre during combustion or restrained by fixing to structural elements. Items were each identified by unique shape where possible, further marked by a binary code cut into them, and then tagged with a small steel label to aid identification after high levels of destruction by firing. ..placement groups Items were divided into four groups according to their proposed transit through the pyre during firing: Group 1: loose: some items were placed unattached in the pyre, to move down freely as the timber burnt away; Group 2: fixed: other items were fixed to immovable objects, the instrument pods, to remain in position as the pyre burnt down past them, to record the effects of temporary exposure to heat at key points; minor data from an item in the hot pit are included here; Group 3: temporarily restrained: the final group was fixed to the corpse, in order to mimic body ornament, which would remain in place in the upper, hottest part of the pyre until supporting bone disintegrated, the fuel load burnt away, and items fell towards the ash-bed. Group 4: on the ground

In the pyre of Jonuks and Konsa (2007: table 3, presenting the condition of artefacts before and after cremation) almost all of the objects initially placed on the pyre were found in the final ash bed. Metal, shells and pottery survived well, horn-antler-bone much less well, and predictably the leather strip disappeared. Burning of items was uneven, with some heavily disfigured, others only sooted. It was noted that the extent of melting and burning observed had little to do with how objects were placed on the pyre, some falling off at the start and others going through the hottest fire relatively unscathed. The pyre, which experienced problems after ignition, was not an intense one, temperatures being somewhat lower and generated over a more extended period than those for pyres 1 and 2 at Guiting Power, where by contrast, items added were highly damaged or destroyed during the fierce heat of the cremation process.

..metal types Items of three types were included, differing in their properties, shape and size (PLATE 2):

Not all damage to pyre-goods need be attributed to the effects of burning. For instance, there is evidence from the Danish Iron Age that intentional destruction of grave- and pyre-goods by bending, parting, or crushing was a normal procedure (Henricksen 2009). There are also indications that such rituals may have a wider European basis and have been carried out during some parts of the

...type 1: representing smaller blades, and items of weaponry with relatively high surface area to weight (TABLE 6). These were of medium (15%) tin bronze, with lead, arsenic, nickel, and sulphur impurities present, cast into flattened, elongate plates, of uneven plan:

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experimental pyres TABLE 6: Survival of 'type 1' bronze items in the pyre (mean weight: 31.1g) item thickness (mm) 1 5-8 2 5-7 3 6.5 4 3-6.5 5 4.5 6 5-5.5 7 3-5 8 2.5-4 9 2.5-3 10 3.5-5 11 5-5.5 12 3-4 13 2-6 TOTAL

initial location wt. (g) 75 *Fm 61 *Sm 55 *Rm 51 corpse 21 *Cu 32 *Cm 19 on ground 14 corpse 12 corpse 18 corpse 21 *Cl 13 corpse 12 hot pit -----404 (100%)

PG

survival

2 2 2 3 2 2 2 3 3 3 2 3 2

low high low low intact intact low intact intact

final wt.(g) b 54 b b 32 19 b 21 12 -----252 (62%)

Note: in TABLES 6 and 7 those items listed 'b' in the column for final weights survived only as highly melted blobs, without clear identification marks, and weighed in total 114g. PG: placement group; '*': denotes the instrument pod on which the item was fixed (FIGS 4, 6).

...type 2: representing more compact metalwork, with lower surface area to weight. These were of tin

bronze (12%) cast as pyramids, 3.5cm high and 2cm square at the base (TABLE 7).

TABLE 7: Survival of 'type 2' bronze items in the pyre (mean weight 45.1g) item

initial location wt. (g) 1 46 *Fm 2 45 *Sm 3 36 *Rm 4 46 *Cu 5 46 *Cm 6 45 *Ci 7 44 on ground 8 48 corpse 9 48 corpse 10 45 corpse 11 45 corpse 12 47 hot pit -----TOTAL 541 (100%)

PG

survival

2 2 2 2 2 2 2 3 3 1 3 2

intact low low intact intact intact intact low intact

...type 3: these items were included with the corpse to provide data on survivability for one standard type of metalwork over a range of sizes (TABLE 8).

final wt. (g) 46 b b 46 46 46 44 b 47 -----280 (52%)

Lengths of copper pipe were used, of external diameter 22mm, and thickness of wall 1.5mm:

TABLE 8: Survival of 'type 3' bronze items in the pyre (mean weight 67.3g) item 1 2 3 4 5 6 7 8 9 10 unknown TOTAL

initial location wt. (g) 151 corpse 118 corpse 113 corpse 78 corpse 71 corpse 52 corpse 39 corpse 23 corpse 16 corpse 12 corpse

PG

survival

1 1 3 1 1 3 3 1 1 1

high intact low high intact low low intact intact intact blobs

-----673 (100%)

Note: PG: placement group.

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final wt. (g) 128 126 34 69 71 29 19 23 16 11 5 -----531 (79%)

experimental pyres ...type 4: these items, of standard size, were included with the corpse to represent smaller items of personal adornment (TABLE 9). Copper rings were

used, of external diameter 24mm, width 7mm, average thickness 1.5mm, and mean weight 4.8g:

TABLE 9: Survival of 'type 4' bronze items in the pyre (mean weight 4.8g) number of rings 20

initial location wt. (g) 96 corpse

PG 3

survival of rings 3

final wt. (g) 15

% survival by weight 16

Note: PG: placement group.

Residual bronze and copper retrieved from the pyre weighed 121g, which represents 7% of the original 1714g included. Since this was melted and fused beyond recognition of its original source, it is not known how it would affect the calculation of total

copper alloy survival (TABLE 10). It is therefore assumed to be derived fairly equally from all four types of metal item, with perhaps more from the smaller items, and not to adversely affect estimation of survival at the level of broader conclusions:

TABLE 10: Survival of all bronze items in the pyre survival of metalwork by type: metal WEIGHT (g) SURVIVAL type before after % cremation 1 404 252 62 2 541 280 52 3 673 531 79 4 96 15 16 ------1714 (100%) 1078 (63%) survival of metalwork by placement group (PG): PG WEIGHT (g) SURVIVAL before after % cremation 1 514 444 86 2 651 413 63 3 549 97 18 ------1714 (100%) 954 (56%)

Metalwork items free to move through the pyre during combustion tended to percolate downwards fairly rapidly towards the cooler, less oxidising conditions of the ash-bed, where they became more protected (general survival rate 86%).

..conclusions Analysis of survival for metal items during cremation indicates the following conclusions: ...the nature of destruction Experiment shows that most copper and bronze objects were damaged in the pyre by melting rather than by the type of complete oxidative destruction possible under more fiercely burning conditions.

Samples fixed in the pyre reflected the intensity and duration of transient heating and the extent of oxidising conditions at those points. Items in the mid and rear of the pyre, lying down-wind and undergoing prolonged and intense heating, sustained most damage. Those items which avoided early intense combustion, which were placed or fell into the lower parts of the pyre, or lay on the ground surface, and which came to be covered by the ash-bed, sustained least damage (general survival rate 63%).

...the effects of position in the pyre on survival of bronze Smaller items of bronze, typical of personal adornment or weaponry, fixed to the corpse or free and becoming entangled, and hence remaining with it in the upper, hottest part of the pyre where conditions were highly oxidising and temperatures reached over 1000oC, were readily destroyed (general survival rate 18%).

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experimental pyres Obtaining a longer burn at lower temperatures results in greatly reduced efficiency. A phase of high temperature is needed to vaporise body-fluids rapidly, so that dried residues can ignite fully and combustion of tissue can become self-sustaining. Failure to achieve such a pulse of high temperature, either for the whole corpse or for part of it, as when firing is uneven in the pyre, results only in a cooking or charring of musculature and bone. Deeper material remains hard and sticky with partly carbonised residue, entirely unsuitable for preparation of a clean sample for interment.

...survival of different types of bronze item in the pyre As would be expected, the general survival rate was higher for items which were bulkier (type 1 [mean 31g]: 62%, type 2 [mean 45g]: 52%, type 3 [mean 67g]: 79%), than for those which were smaller, with higher surface area to weight ratios (type 4 [mean 5g]: 16%). This all suggests that finds from pyre-debris are unlikely to reflect well the presence of any smaller personal items such as body ornament. ...micro-structural changes to bronze induced by cremation Microscopic analysis of bulkier metal items of a type which survived experimental cremation well indicates that alteration of their micro-structure clearly reflected the conditions to which they had been exposed. Re-heating items of cast 10% tin bronze to about 700oC, a temperature to be experienced within most parts of the pyre for differing durations, destroys the original dendritic micro-structure of the metal, whilst grain shapes remain unaltered, and it is also possible to detect the presence of an oxidising or reducing environment. This suggests that such items from Bronze Age pyre-debris could yield useful information about the nature and placement of pyre-goods. However much of the original sample of bronze will have been damaged beyond retrieval, given high oxidation, and comminution to further droplets readily corrodable in the burial environment. Survival for analysis of much smaller damaged bronze in the archaeological record is therefore not to be expected, and the general sample unrepresentative.

A compact pyre containing about a tonne of fuel is more than sufficient for complete cremation of an adult corpse, provided it is well structured, and need not be added to once fired. Certainly, at full firing, close approach for stoking or tending is not physically possible in view of the intense radiation, so any intervention for either pyre or corpse would be more likely towards the end of the combustion sequence. ..substitution of animal for human corpses There are reservations imposed on application of data from cremation of animal bone to that of humans, because of differences in anatomy and bone microstructure. It is for this reason that conclusions drawn from the experiments are general and attempt to transcend detailed differences in anatomy. It should also be noted that the main emphasis of these experiments was interpretation of pyre structures, with cremated bone essentially a by-product and its analysis a secondary consideration. ..degree of survival Although disarticulation and considerable fragmentation of bone occurs during experimental cremation much of it survives as larger fragments, or as skeletal elements retaining near-intact form. Larger fragments of skull, vertebrae, long-bone, and rib can all be found on the ash-bed even of efficient high-temperature pyres such as 1 and 2 (PLATE 7). The highly oxidised nature of this bone indicates the efficiency of the combustion process. This ability of bone to survive cremation as larger fragments contrasts with the generally comminuted condition of cremated bone deposited in archaeological contexts which, despite allowing for inevitable damage after burial, indicates the common practice of crushing bone residues before deposition.

-survival of organic materials An 800g sample of grain, included with the corpse, was completely burnt, no carbonised grains being retrieved from the primary ash-bed. Samples of organics placed on the corpse (non-meat foodstuffs), 1157g in total, were almost completely burnt away, leaving only glazed residues, readily comminuted and dispersed beyond identification. Samples of prehistoric pottery of Bronze Age type (hand-made, of fairly hard fabric, and with shell-grit filler) placed on the corpse, retained most of their weight (399g before, and 326g after cremation), but became extremely friable. They disintegrated readily on handling to a condition unlikely to be identifiable against inclusions in natural sediment.

..relationship to the original body weight of the corpse The sheep corpse, maintained at a fairly standard weight throughout experiments (65-80kg), was typically reduced to between 1.5 and 1.8kg of well-cremated and easily retrievable bone. In the pyre of Jonuks and Konsa (2007) a 100kg pig was reduced to 2.7kg of bone residue. The ratio of body-mass to residual cremated bone is similar in

-analysis of cremated bone ..the format for effective cremation The effectiveness of cremation depends on a particular format for combustion: generation within the pyre of an intense phase of burning, reached soon after ignition, in which temperatures between about 700 and 1000oC are achieved and then maintained over a period of about 2 hours.

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experimental pyres the majority of white, highly calcined and heat-shattered fragments, to include some merely well-cooked blackened bone with organic residues still present.

both cases, being 1:0.023 in this programme and 1:0.027 for Jonuks and Konsa. Values for conversion of bodies to cremated bone residues (McKinley 1993) vary according to age, sex, stature, and nutritional status but for human females average 1.8kg and for males 2.7kg.

Deliberate experimental cremation under less than ideal conditions, involving poor pyre construction, non-axial ventilation by wind, use of damp, or unsuitably-prepared wood, wet weather, or premature removal of cremated remains from the ash-bed, all resulted in less complete and uniform burning of the corpse. Alternative orientation of the corpse with either the head or the legs up-wind did produce some initial increase in burning of whichever bone lay at the hotter, down-wind end. However, the effect was not consistent, and differences in combustion of the body apparent during the earlier stages of cremation become evened out as bone sank towards the ash-bed for final burning away of residual organics. If the pyre is not fired end-on into the wind, partial burn-out, and subsequent outward collapse of the superstructure can occur, at its worst taking the corpse with it, resulting in incomplete, disorderly cremation. Cremation in wet weather is certainly difficult, even using dry wood, and especially so if use is made of systemically damp fuel-wood which has been exposed to the elements over winter months. Here there is real difficulty in reaching the sustained high temperatures required to render operation of the pyre independent of adverse conditions. The unsatisfactory results from using too little fuel at too low a temperature is well illustrated in Plate 8a.

..stages in the cremation of bone Cremation of human bone in a furnace at temperatures up to 1200oC for 1-3 hours, in alternative environments rich or poor in organics, and with these additives absent, has been described in Walker et al. 2008. Four main stages of transformation of bone during increased burning were distinguished, each with corresponding textural and colour changes (ibidem, figs. 1-2): dehydration, decomposition, inversion, and fusion with, during the final stage, bone becoming calcined and salts fusing at prolonged temperatures over 800oC, changing colour to blue-grey or white. It is to this latter stage that cremated bone from pyres 1 and 2 belong, confirming the efficiency of oxidation therein at temperatures above 1000oC. The colour of burnt bone gives a general indication of firing conditions, ranging from black from charring around 400oC, to blue-grey indicating incomplete oxidation between 500 and 700 oC, with white indicating complete oxidation over 800 oC. ..unevenness of burning and its interpretation The uneven state of burning in cremated bone often indicates that a corpse has been subject to uneven heating (Brothwell 1972) as noted, for instance, at Sproxton and Eaton (Clay 1993). This general observation has been open to varied interpretation. It could suggest differences in temperature experienced by a corpse at various levels and positions in the pyre. There are cases where differential burning of bone has been used to suggest the position and state of the body or its limbs. For instance, at Balnaguard (Perth and Kinross) less burnt arm-bones may indicate limbs extended towards the cooler margins of the pyre (Mercer and Midgley 1997). At Ballybar Lower (Carlow) reduced burning of the cranium suggested that the head may have been protected by some covering (Troy et al. 2010).

Patterns of differential burning have been used to suggest that the corpse may have been cremated on the ground, with the pyre constructed over it. Differential burning of bone encountered amongst Saxon cremation deposits at Illington, Norfolk (Wells 1960) was used to suggest that the corpse was placed on the ground, not on top of the pyre where cremation would be much fuller. It was proposed that such grounding would also reduce scattering, and thereby ease collection of cremated bone. A pyre of very considerable size was also deemed necessary for complete cremation, possibly encouraged by stoking as the ritual progressed. None of these interpretations are supported by the present set of experiments. Experimental cremation in this programme of such a grounded corpse, under good weather conditions, does indeed result in far less efficient cremation than when the corpse is placed in upper hotter levels, and there seem to be no advantages whatever in use of this method since heat from much of the fuel-load is wasted. Irregularities in burning of bone are probably best explained by variations experienced in the upper pyre and during descent of the burning corpse.

Orientation of the corpse within the pyre in relation to the hotter up-wind or cooler down-wind zone of the pyre could also affect parts of the skeleton differently. Inadequacy of the fuel-load, partial failure or inefficiency of burning caused by wind-change, or the adversity of wet weather conditions prevailing at the time of the cremation, acting to quench the pyre, could all contribute to reduced burning of bone. However, even under the very efficient firing achieved in these experiments (pyres 1 and 2), incomplete burning of bone was noted, ranging from

..charred soft tissue residues Significant quantities of highly charred soft-tissue

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experimental pyres vertebrae can be readily removed, with finer bone fragments separable from ash by sieving through fingers, or winnowing between cupped hands. There is some evidence that clearance of bone from the ash bed was not entirely scrupulous. Inclusion of charcoal within many deposits of cremated bone from round barrow sites (Guiting Power 3: the primary cremated deposit from the central location and an auxiliary pit) suggests that either a bone-enriched charcoal fraction was considered sufficient, or indicates deliberate addition of char to the hand-picked bone. Perhaps more likely might be inclusion of charcoal during less scrupulous extraction of the most comminuted bone, simply by scraping up groups of smaller fragments within their general matrix.

residues, friable and spongy in appearance, were evident in primary residual pyre-debris produced by the experimental cremations (PLATE 7). These carbonised tissues could be tracked through the pyre during their formation in the mid, and later phases of cremation, and were seen to originate mainly from the internal organs of the corpse. Such residues may have been important products of cremation, albeit fragile ones, deemed worthy of reverent disposal in addition to bone, with their importance eclipsed in the archaeological record by the more durable nature of the latter. Secure interment of such residues would have been possible only within a receptacle, such as an urn, common containers for cremated bone, their partially filled interiors often indicating that other more perishable items may have been present.

Experimental data on collection of cremated bone from the ash-bed provides a guide to efficiency of retrieval, within defined limits of time spent and care taken. Within an hour and a half, one individual can easily separate by hand a complete and fairly uncontaminated set of cremated bone fragments, roughly equivalent to an adult human skeleton, from cooled residual pyre-debris, with well over 95% efficiency. Checking the effectiveness of this separation by dry sieving the scrutinised ash through very fine mesh shows that an average of 2-3% is missed, mainly very small particulates. The ease of this sorting process suggests that cremated deposits which are obviously partial or token are not so because of any inherent practical difficulty in retrieval of bone, but for additional, deliberate reasons.

..copper staining of cremated bone Copper staining is often noted on cremated bone, as at Guiting Power 1 and 3 (Marshall 2007a; 2007b), or at Sproxton and Eaton (Clay 1993). Cases of possible copper and other staining of cremated bone from Bronze Age contexts were noted by Troy et al. (2010). This residue may indicate the former presence of a copper-alloy item, either held on the corpse as personal adornment, for instance an arm-ring which came to stain the bone on melting, or by other transient contact with such metal during or after the cremation. It has been suggested that the presence of such direct staining could indicate de-fleshing of the corpse before cremation, either by exposure or perhaps butchery. Experiment by the author clearly indicates that this staining-effect can be induced by cremation of a corpse with flesh present, as long as the bronze is sufficiently substantial to remain after most flesh has been burnt away. Alternatively, other work suggests that such staining can be the result of natural mineralogical processes (Hermann 1972).

Partial and token cremated deposits may suggest anything from careless retrieval, to divided deposition within the simplest rite, to considerable elaboration and extension of the whole process, resulting in complex and socially important patterns of retention and disposal of human remains (Bruck 1995; Parker Pearson 1999; Waddell 2000).

..scattering and containment of cremated bone Despite the relatively close fit of a standard box- or log-edged pyre structure to the shape and size of a prone human corpse, containment of most bone over the final ash-bed occurs naturally, and with collection straightforward, given sufficient cooling and time for retrieval. No sub-structures, such as a scoop under the pyre, are required to facilitate collection of bone, which falls to lie over the surface of the ash-bed.

An adult human skeleton, as cremated efficiently, produces 1-1.5kg of residual cremated bone. Scrupulous collection (about 95%) of bone from primary residual pyre-debris would, therefore, produce a weight of bone within the same approximate limits, and provide a reference weight against which to compare the completeness of a cremated bone deposit. Using such criteria for completeness, there is a tendency for primary cremated deposits under round barrows to represent a higher proportion of the skeleton than do satellite or secondary deposits. This may indicate the higher degree of care taken with this initial event, which was perhaps of singular dedicatory importance for the monument, involving disposal of an individual of sufficient status to merit such attention. Cases of scrupulous retrieval can be seen in primary deposits from round barrows at Guiting Power 1 and 3, Glos. (Marshall 2007a; 2007b), Sproxton and Eaton, Leics.

..retrieval of cremated bone from the ash-bed Experimental retrieval of fragmentary cremated bone from residual pyre-debris, cool enough to handle easily, demonstrates that extraction requires no equipment, and its effectiveness is largely dependant on the time spent doing it. Much of the cremated bone lies in a layer about 10cm thick over the centre of the ash-bed, in very approximate anatomical correspondence to the original skeleton, but with slightly wider dispersion (FIGS 3,14; PLATE 7). Larger fragments and complete bones such as

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experimental pyres (Clay 1993), Portsdown, Hants. (Nicholls 1987), and Ashey Down, Isle of Wight (Drewett 1970). Examples of less complete retrieval occur at cemeteries such as Simons Ground, Dorset (Hazzledean 1982), Coneygree Farm, Notts. (Allen et al. 1987), and Pasture Lodge Farm, Lincs. (Allen et al. 1987).

..shape: A generally sub-rectangular outline to the burning would result from a box-pyre elongately-shaped to carry a single prone corpse. This burnt shape would correspond more closely with the original pyre-site if cremation was carried out under calm conditions. Any wind would act to spread radiant burning to the down-wind side, thus modifying the shape of the pyre-base, as visible and detectable by instrumental means. Such deviation in shape of the pyre-base can be used to infer conditions during ancient firings.

..interpretation of cremated deposits from archaeological contexts Cremated deposits from Bronze Age round barrows represent the expected bone mass from the original skeleton to varying degrees, minus a fraction, often relatively minor, which could represent inevitable loss of smaller fragments during retrieval from the ash-bed. As shown by experiment, during cremation a proportion of bone becomes finely comminuted and thereby rendered difficult to retrieve by hand-picking, even by careful winnowing. Larger bone may simply be missed during sorting from residual pyre-debris under any circumstances, but especially so if the debris is still hot. Further loss may have occurred during any crushing of the remaining bone, as part of its preparation for final disposal (McKinley 1993, 1994). Further incidental sources of loss, especially for finer bone particulates, during the interval from original deposition to archaeological retrieval, include resorbtion of bone in calcium-poor, or acidic soils, and loss during excavation by inadequate screening procedures.

..area: Direct burning occurs over the contact zone under the original pyre-site, and extends around its margins where radiant heat and falling burnt debris bake the exposed surface. The entire zone affected includes an area about twice the original width of the pyre and about 1.5 times its original length. ..thickness: The burnt crust is little more than a centimetre thick at most as gauged visually, but up to about 5cm maximum in terms of enhanced magnetic susceptibility (MS). The crust is of uneven thickness and MS enhancement, the result of differential burning over the pyre area. The fragility of this crust and its vulnerability to damage or complete truncation during aggressive pyre clearance is important in considering methods for prospection of pyre-sites, and interpretation of the surfaces where these are identified, or are expected to occur.

Alternatively the missing fraction could be explained by deliberate retention of items for purposes of ritual. Fragments of bone, perhaps from specific anatomical features such as the skull or long-bones, may have been deliberately retained by participants for other ritual purposes. For instance, there is evidence for placement of what could be retained bone in the cairn over the primary cremated deposit at Guiting Power 1 round barrow (Marshall 2007a).

..patterned burning: The areas of highest burning over the ground surface occur just beyond the original base tier of the pyre, where fierce radiation and highly oxidising conditions occur. The general pattern of burning is an irregular sub-rectangular ring of redder, highly oxidised sediment lying around the margins of the pyre. This surrounds an inner area of blacker ashy baking located more centrally under the ash-bed, where surfaces have been shielded from fiercest heat and fully oxidising conditions. The areas of highest burning occur towards the down-wind side of the pyre, where prevailing wind produces the most intensely oxidising conditions.

The practice of partial deposition or burial of cremated bone and pyre-grave goods, as observed in the later Iron Age cemetery at Brudager (Denmark) but observed far more widely and earlier, during the Bronze Age, termed the pars pro toto ritual, has been well discussed by Henricksen (1998). Here, graves of the later Iron Age usually contain only a few grams of cremated bone, but in the later bronze age the proportion of the corpse represented is far higher, although instances of near complete deposition of cremated bone are rare.

..orientation: Given the need to produce complete combustion which spreads efficiently from the ignition-point into the pyre, its alignment end-on into the wind would be an optimum orientation. The prevalence of westerly winds in southern Britain could therefore, on practical grounds alone, have resulted in a preference for a generally E-W orientation of pyres. It might have been necessary to establish the pyre-axis well before the cremation, by application of a general rule for expected wind direction, as for instance in any cases where the corpse was required to lie for a prolonged period beforehand, displayed on a raised

Properties of pyre-bases: conclusions Experimental simulations at Guiting Power suggest that box-pyres, fired on a clay substrate, produce ground features with some or all of the following properties: -the base of the pyre is marked by a thin burnt crust (FIGS 7-12; PLATES 4-6)

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experimental pyres detected, especially if large enough to produce characteristically non-human fragments. Prehistoric pottery is too friable to survive, and thermal fracturing reduces it to an amorphous sediment-like residue. It remains possible, however, that any item found over a pyre-base, even if burnt, might be extraneous debris not linked to the cremation event, being either residual, or inadvertently trodden in during subsequent activities. All of these points can be illustrated with reference to Guiting Power 1 round barrow (Marshall 2007a).

platform-structure. However, if the pyre was laid immediately before cremation, a task which could take as little as an hour or so when using already-assembled supplies, the axis could be matched precisely to the prevailing wind direction at the time. Other factors, of a ritual nature, may have affected the choice of pyre-axis, perhaps with some basis in the solar cycle, as for instance alignment towards westerly sunsets, this direction having a widespread link with death. -low levels of associated pyre-debris might be expected Residual ash and char form a compact ash-bed, spreading little beyond the original pyre-site, and in efficiently burnt pyres this debris amounts to only about 0.5% of the weight of the original timber. Remaining fire-debris can be further reduced during the hours required for fuller cooling, as wind acts to remove finer particulates. Such winnowing would also tend to be increased if cremation took place on relatively exposed upland, a frequent location for round barrows.

Detection of pyre-bases Comparisons between the plans of pyre-bases, as made visually and as obtained by measurement of magnetic susceptibility, emphasise the essential need for instrumental survey to produce a fuller version which includes non-visible enhancement (Marshall 1998). Radiant heat from a pyre causes non-uniform magnetic enhancement in the ground at its periphery which need not be accompanied by clear changes in colour. Consequently, survey using a Bartington MS2 susceptibility meter, fitted with a D-head, should be undertaken at maximum resolution, sampling at intervals of perhaps 20-25cm, preferably as replicate surveys.

-certain pyre-related structures might survive The ignition-point of the pyre might be marked by a scrape in the surface at one end, perhaps the most likely windward edge. Uprights for a platform bier might be seen as post-sockets infilled with char-enriched sediment, but are most unlikely to persist as charred post-bases remaining in place, since burning of buried wood is very difficult to achieve.

Cremation and firing in pits The series of experiments included a series of small pits, about 50cm in diameter and 40cm deep, cut into clay substrate, in which a range of firings were carried out, to examine the extent to which combustion was reflected in burning on the sides and base.

-preservation of the pyre-base might be poor Fairly severe damage might be expected, given the patchy and thin nature of the burnt crust, the extent of trampling associated with clearance and screening of pyre-debris, then burial of the cremated deposit within the pyre-base and subsequent covering of the site. Patterning in the burnt crust might be removed or blurred, at least visually, perhaps leaving a clearer picture to be obtained only by instrumental survey of sub-surface enhancement. Truncation of such a patchily-burnt surface might result in the original feature only surviving as separate component anomalies.

These were intended to supplement interpretation of such features sometimes found at round barrows. For instance, an auxiliary pit at Guiting Power 3, containing what may be part of the primary cremated deposit together with re-deposited pyre-debris (Marshall 2007b), bore no trace of burning nor increased magnetic susceptibility at the sides. It was hoped that experimental replication would help distinguish whether the pit was filled directly from the hot ash-bed, or with cooled scattered debris collected some time afterward. Experimental deposits of hot ash and cremated bone produced no visible burning, but slightly increased MS over the interior of pits, suggesting that these alternatives could perhaps be distinguished. The pit at Guiting Power 3 therefore appears to have contained cooled re-deposited pyre-debris, acting as a repository for residual bone and charcoal. These experiments, and others (Gibson 1986), indicate that it is difficult to burn the interior of such a pit without an active, well-structured, and aerated fire.

-finds characteristic of pyres might occur Despite detailed screening of the ash-bed during retrieval of bone, tiny fragments of such bone are likely to remain over the surface to suggest identification of the burnt feature as a pyre-base. Residual pyre-goods might also be present, but only those of a type likely to survive exposure to high temperatures. Flint, or items of harder stone would persist as highly heat-fractured fragments. Copper might survive as metallic droplets, staining on bone, or as chemically-altered derivatives, although these are too water-soluble not to be readily leached. Animal bone survives cremation and can be

The three burnt pits at Carneddau 1, Powys (Gibson 1993, fig.15) were different from this experimental repository-pit, in that here the sides were indeed burnt and the fills were of sufficiently high MS to

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experimental pyres cremated human bone over it (ibidem, figs.3,4; this paper FIG 14b). Unlike many others which have undergone disturbance by raking, clearance, or erosion, this pyre-site may remain relatively intact, preserving the true condition of its ash-bed after final firing, since it was sealed under collapse from the mortuary structure, with intact underlying timbers further suggesting an absence of disturbance. The distribution of bone does not appear to them to reflect the pattern to be expected after orderly descent of a prone articulated corpse onto an ash-bed, the scatter appearing to be reduced in quantity and differently dispersed. They further suggest that the disorder in the scatter of cremated bone at Linga Fjold (Orkney) (Downes 1995), originally seen as resulting from raking of the ash-bed, may be capable of similar reinterpretation in terms of cremated body-parts. In view of such a possibility they suggest that unqualified use of the term 'pyre' might be prejudicial, in inferring disposal of a complete corpse.

indicate in situ burning, perhaps cremation of disarticulated, excarnated bone. Other experiments carried out at Guiting Power indicate that such burning is certainly possible if firing is carried out with dry, calorific timber, especially under windy conditions to remove ash and aerate the fire, and with judicious intervention by pokering of the fire. Single and multiple use of pyre-sites Using the extent and depth of burning over the ground surface produced by standard experimental box-pyres 1 and 2 it may be possible to distinguish between single and multiple use of pyre-sites amongst archaeological examples (FIG 15). Single use is suggested by areas of visible burning at Letterston 2, Brenig 40, and Brenig 42 which are less than the standard but similar to that of the smaller experimental pyre 3 (FIG 10). Brenig 40 and 42 also have post-structures, possibly pyre framing, which would match the area of a small box-pyre.

Although the corpses cremated were those of surgically-modified sheep rather than human, the experimental work in this analysis does provide a useful preliminary indication of the pattern of bone fragments generated by cremation of an intact, articulated, prone skeleton, what might be termed for convenience here a 'standard cremation' (FIG 14a). In a well-structured and efficient experimental pyre, fired at high temperature, the burning corpse descends into the collapsing fuel-load in relatively intact form, to disarticulate and fragment in the lower levels when most tissue has been removed, with elements becoming anatomically displaced as they fall through burning timbers. Further damage from falling timbers and displacement by rolling adds to the disaggregation. The bone is scattered fairly evenly over most of the ash-bed, remaining largely within it, and shows a fair degree of survival as larger fragments, with articulation often present (PLATE 7).

Similarly, burnt areas at Trelystan North, Amesbury G71, and Sproxton (although half destroyed) seem to match the standard. Trelystan North also has a post-structure slightly smaller in area than the standard. Amesbury G61 and Balnaguard have burnt areas in excess of the standard and hence appear to represent areas of reuse and/or of larger pyres. At Amesbury G61 the post-structure within the spread of burning is about the same size as the standard box-pyre area. At Balnaguard two of what may have been many phases of firing were detected, resulting in a bed of burnt debris about 15cm deep which contained a scatter of cremated human bone. Use over a fairly lengthy period for multiple cremation seems evident, perhaps producing those deposits which lie in small cists around the pyre-site. The burnt area is equivalent to about two unit box-pyres side by side, but reuse for a series of single pyres, these varying in placement around a central zone, would be expected to result in a larger spread.

In contrast, the scatter of cremated bone at Pencraig Hill appears distinctly uneven, with four main concentrations, each containing a mixture of skull and limb fragments. Whatever its cause this is unlikely to represent a standard cremation. If the bone is not residual from previous firings on the site, does not represent different token deposits made onto the pyre-site, is not the unsorted residue from a normal retrieval, or has not fallen from some repository originally above, then cremation of body-parts is certainly a possibility, perhaps as a variant on standard utilitarian practice.

Cremation of a full or partial corpse The need to address problems of interpretation, using data from experimental cremation and from well-preserved pyre-sites rather than by analogy and conjecture, is stressed by Duffy and MacGregor (2008). Citing evidence for the widespread occurrence in the archaeological record of disarticulated human remains and of token cremated deposits they propose that the idea of a standard cremation involving a prone individual on a dedicated pyre be revised to include the possibility of variant practice involving only body-parts. Using the Neolithic timber mortuary structure at Pencraig Hill (Lothian) as an example of the northern British tradition of cremation, to argue the point, they cite the case of its axial pyre-site and the distribution of

If such partial or disarticulated cremation is to be addressed in the archaeological record and any supporting experimentation justified it is essential to consider under what circumstances such a rite would have been carried out and its overall likelihood.

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experimental pyres correspondence would be expected for an intact corpse, but less so for those undergoing disarticulation, because dispersal of the latter in the pyre would begin earlier in descent, with more latitude for slippage and rolling.

A selection of reasons can be grouped briefly as follows, first considering reasons for disarticulation in the corpse to be cremated, then for processing its individual body-parts: -as part of the standard utilitarian rite ..dismembering a whole fresh corpse as part of a standard cremation The resultant body-parts could have been placed in different parts of a standard pyre, more compactly in a smaller pyre, or parts only cremated, with the rest disposed of elsewhere. This might have allowed cremation of remains to be spread over time, or shared between different social groups and locations. However, butchery of a routine corpse in this way would seem a somewhat messy technical challenge, procedurally unnecessary, and potentially impious.

Such control data would be simple to obtain, but the problem arises in applying them to archaeological contexts, confidently comparing like with like, since the intact nature of an ash-bed and its associated bone is very difficult to verify, and selective retrieval of bone or partial clearance could still be argued.

Section 3: APPLICATION OF EXPERIMENTAL DATA COMPARISONS BETWEEN DATA FROM THE EXPERIMENTAL CREMATIONS AND FROM PYRE-SITES EXCAVATED AT GUITING POWER 1 ROUND BARROW (FIGS 16-22) Excavation of Guiting Power 1 round barrow (Marshall 2007a) produced three pyre-bases of different types, each well preserved, and from a specified archaeological context, all of which were surveyed and excavated with analysis using existing experimental data clearly in mind (FIG 16).

..disarticulating a decayed corpse after storage, excarnation, or exposure Shorter-term storage-burial may have been carried out on the grounds of convenience, for instance to avoid practical problems in cremating during an inclement season such as winter, when dry timber was in short supply. During such a period some potential for disarticulation could develop. However, bodies exposed over the longer term on platforms or in exposure grounds, or encisted or inhumed corpses would certainly provide an abundant source of disarticulated remains. Their final disposal in total or part could involve cremation.

On balance it seems more likely that utilitarian whole-body cremation was the dominant rite, with many barrows producing supporting evidence, but with token and partial deposits of human bone perhaps requiring explanation beyond selective and incomplete retrieval. There is the distinct possibility of variant practice, using disarticulated material perhaps from decayed rather than fresh corpses, taking place at both local community barrows and at other mortuary structures of more dedicated ritual significance.

Types of pyre at Guiting Power 1 -the primary ring-pyre The base of a large, central, primary ring-pyre lay over the cleared ancient ground surface, at the centre of the area to be covered by the ensuing barrow mound (FIGS 18,19). After cremation the ash-bed was cleared and a cremated deposit (an adult male, full deposit) was placed in a pit-scrape at the centre of the pyre-base. This deposit was without obviously associated artefacts, except for one flint core (burnt, possibly primary or satellite pyre-goods), and a fragment from a broken arrowhead of barbed-and-tanged type (unburnt, possibly primary grave-goods), both perhaps gender-related items. The cremated deposit was covered by an elongate cairn of loose rubble, aligned E-W. The entire area of the ring-pyre, encairned over its central sector, was then covered by the inner core of the clay mound for the barrow, without much delay, certainly before the cairn and surrounding pyre-base could sustain much damage. The large size of the pyre, in excess of that required to cremate a single individual, suggests that the firing was festive as well as functional, perhaps part of the dedicatory rituals required for establishment of the monument.

The question of whole versus partial cremation is amenable to experimental investigation. First of all the degree of correspondence between corpse and derived scatter of cremated residues in the ash-bed needs to be determined in replicate using both intact human bodies and decayed corpses, in a variety of relevant positions, such as prone or crouched. A fair

-the satellite box-pyre (stack-type) After the central area had been mounded with clay and covered the area of the primary ring-pyre, a small stack-pyre was set near the limit of the growing mound-core, an infant was cremated, and the remains disposed of at an unknown site. Only a few fragments of cremated bone remained on the

-for magico-religious reasons There are many possibilities here, with many useful ethnographic sources, for instance cremation of bones as part of seasonal ritual, or of body parts taken in warfare or as punishment. Dismemberment might also have been used to nullify an individual who was considered to be possessed or who was diseased.

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experimental pyres pyre-base was thoroughly cleared of debris, and the area then covered without delay by a rubble platform extending out from the kerb of the barrow. The cremation may well have been dedicatory for this additional structure, rather than indicating a more routine cremation in a secondary location.

uncleared ash-bed. At about the same stage in the construction sequence of the barrow, burnt debris, including fragments of animal bone and charred grain, was scattered over the flanks of the mound, suggesting auxiliary ritual, of which this cremation may have formed a part. This cremation may well have been highly ritualised, rather than indicting the necessary disposal of a naturally-dead infant corpse, and was perhaps linked with ceremonies marking near completion of the basic barrow mound. Similar deposition of a cremated infant was also carried out on the growing flank of the clay core of the barrow at Guiting Power 3 (Marshall 2007b).

Detailed magnetic susceptibility (volume MS) survey of the entire surface under and around the barrow provided instrumental in addition to visual definition of burning. A series of other candidate areas for pyres or fires were identified, a few associated with weakly fire-reddened sediment, hence possibly features extensively cleared of debris, and none producing cremated bone or other associated finds (FIG 17).

-the secondary box-pyre After completion of the barrow monument, and an interval of use sufficient to require replacement of the stone kerb revetting the mound, a box-pyre was fired just beyond the margin of the barrow, and a cremated deposit (an adult female, possibly two) was placed in a pit cut through the pyre-base. Very few artefacts were associated, but present were a flint scraper (burnt, possibly primary or satellite pyre-goods), and small bronze point (possibly satellite grave-goods), both perhaps gender-related. Low survival of smaller bronze items placed in experimental pyres suggests that this intact point is very unlikely to have passed through the pyre, and hence may represent grave- rather than pyre-goods. After cremation this

The three known pyre-bases definitely identified provide excellent structures for direct comparison with the experimental pyres, since they took place on a very similar clay substrate and were subject to similar methods of survey. Comparative analysis: box-pyres at Guiting Power 1 (FIGS 16,20-22) The properties of pyre-bases excavated at Guiting Power 1 round barrow, and details of comparable experimental pyres are as follows (TABLE 11):

TABLE 11: Box-pyre-bases at Guiting Power 1 round barrow PROPERTY secondary pyre satellite pyre -------------------------------------------------------------------Cf: expt. pyre 1,2,3 3 pyre type ?stack or framedburnt crust shape and approximate width/length (m) visual rect: 1.1 x 1.7 from MS rect: 2 x 2.5 ?original pyre rect: 1 x 1.6 orientation W-E thickness (max) 1cm ring pattern slight indication from MS burnt plumes mainly lateral (MS) post holes absent pyre-debris re-deposited in pit/ some over base corpse adult: young female cremated residue near full in pit/ half over base burial pit cut into pyre-base oxidation of bone high finds associated flint scraper, bronze point related structure few placed stones on base preservation base well cleared sealed under laid rubble beyond kerb date early 2nd millennium BC Key: rect(angular); crem(ated); frr fragments.

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?stack rect: 0.8 x 1.2 ovate: 1 x 1.5 rect: 0.5 x 1 SW-NE 3cm none beyond ?back end (MS) absent primary residual ash left over base infant very partial few frr. over base none at pyre-site high none none low ash-bed left intact clay core of barrow early 2nd millennium BC

experimental pyres that achieved in experimental pyres. It also indicates easy retrieval of bone from the small, well-cooled residue of ash left by complete combustion, after deflation of finer material by wind, stronger in this upland location. The fragmentary cremated deposit buried in the secondary pyre-base indicates further reduction of this bone after collection by simple crushing. The very high proportion of the skeleton represented in the secondary cremated deposit indicates that collection was very painstaking, with missing bone explainable as unretrievable particulates, matching retrieval rates recorded under careful experimental conditions.

Data from experimental box-pyres allow further interpretation of these excavated pyre-bases, adding detail to discussion of original structure, operation, the cremation process, and what any associated artefacts may represent: -size The secondary pyre-base was of a size close to those generated by experimental pyres 1 and 2, and hence can be identified as a typical adult-sized box-pyre, as further confirmed by the associated cremated deposit of an adult female (perhaps partial of two individuals).

-grave-goods The near absence of artefacts associated with these pyre-bases as pyre-goods could be readily explained by destruction of all but the most resilient materials, under temperatures which could have reached 1000oC, and even higher under conditions of forced ventilation by wind. The only pyre-goods from the period in question which are likely to survive are bronze and flint, both of which present in the pyre-base of the secondary cremation, the latter also associated with the primary cremation deposit.

The satellite pyre-base, a box-pyre of stack-type, was only large enough for an infant or juvenile, and again token infant bone retrieved from the ash-bed supports this reduced capacity. In both cases the original size of the pyre can be gauged from the burnt pyre-bases, likely covering an area just within the visibly burnt patch, and well within the limits of surrounding magnetic enhancement caused by radiant heat. -shape The basically sub-rectangular shape of both pyre-bases would conform with the original shape of the pyre itself.

-other unidentified fire- and pyre-sites Although many possible pyre-bases can be clearly identified by larger-scale deposition of cremated human bone within them (FIG 15), this association is not always the case, as in the case of very minor bone marking the satellite pyre at Guiting Power 1 round barrow. Also at this site, other areas of burnt sediment, not apparent visually but only as magnetic anomalies from MS survey (FIG 17), unassociated with human remains, show similarities with anomalies produced for experimental pyres. Screening such areas in detail for traces of bone or its chemical derivatives, may help identify such features as candidate pyres, and provide information important to general interpretation of round barrow sites.

-orientation The long axis of both pyre-bases conforms well with the practical need to obtain even and complete combustion by aligning pyres on this exposed hill top end-on into prevailing wind, in this area generally westerly. -firing The strength of magnetic anomalies marking these excavated pyre-bases indicates an intensity and efficiency of burning comparable with those achieved by experimental pyres 1 and 2, a conclusion further supported by the highly oxidised nature of cremated bone present. In the case of the satellite pyre, the absence of much pyre-debris suggests that manual clearance of the ash-bed took place, but may have been little needed, given deflation of debris in the wind-swept location and the near-complete combustion seen in comparable experimental pyres. The thin bed of ash, with very little charcoal, preserved intact by rapid mounding of the barrow, which marked the base of the satellite pyre, further indicates the efficiency of firing and extent of ash deflation.

Analysis therefore suggests that pyre-bases obtained by experiment compare well in general morphology with those from excavation, and provide an important supplement for their interpretation. However, one apparent difference suggests that pyres like those discovered at Guiting Power 1 round barrow may have undergone even more efficient combustion than the simulations. -patterns of burning over excavated pyre-bases The two excavated pyre-bases at Guiting Power 1, satellite and secondary, do not show clear division into a relatively unburnt central zone within the more oxidised ring of aerobic burning which occurs around the margins of the pyre-base, as clearly as seen for experimental pyres 1 and 2 (FIG 7). From the visual and MS data, the secondary pyre shows the ring weakly, the satellite not at all, and so in both of these

-processes of cremation The absence of a general scatter of cremated bone around these pyre-bases suggests effective confinement of the corpse within the body of a pyre structured to collapse inwards, in a similar manner to

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experimental pyres Experimental simulation of such a perched structure did produce a slightly more uniformly burnt pyre-base, but not to the extent observed in the excavated examples. Such perched pyre-structures are possible during the prehistoric period, and at certain sites large charred timbers survive, perhaps derived from substantial basal or lateral timbering in the frame of the pyre (TABLE 5).

excavated cases the centre of the pyre-base had also been fairly uniformly exposed to high levels of intense, oxidative burning. This could not have occurred if the base had become sealed within an ash-bed, which promotes reducing conditions and reduces baking and magnetic enhancement of underlying sediment. Major alteration by bioturbation of the pyre-base after burial would not spread burnt crust laterally to the extent required, the only physical movement of material possible would be a slight thickening and dilution of the crust, caused by natural processes within the soil. Accumulation of iron pan at the burnt surface was not observed, nor would it change the nature of the magnetic anomaly.

There is, however, a simpler explanation for the more uniformly burnt pyre-base, which again has been validated in this series of experiments: ..prolonged contact burning within the ash-depleted char-bed Experimental pyres 1 and 2 were carried out in a relatively sheltered valley location, under conditions of light wind, and resulted in a fairly well developed ash-bed, which stifled fiercer final burning of the ground. This choice of calmer conditions was deliberate, in order to provide control data as a base-line for comparison with firings under changed weather. Further experimentation showed that for firings under high wind, in exposed upland locations, during the final stages of cremation, much more of the lighter residue was blown from the ash-bed, allowing development of hotter, well-aerated char close to the ground surface. Individual smouldering logs which fall from any pyre, and lie on ground beyond the margin, also produce uniform red, well-oxidised scorch marks, and further serve to illustrate the principle.

More uniform basal baking of this type could have occurred in two ways: ..perched pyres: Raising the main fuel-bearing structure of the box-pyre above the ground, on larger basal timbers, would provide an air gap under the pyre, initially containing a small starter-fire at the windward end, and thereafter aiding burning by allowing increased ventilation of the main fuel-load (PLATE 8c). Intense radiant burning could occur as the earlier stages of fire swept along the underside of the perched fuel-load, and on into upper levels. Continued baking would depend on the ground surface remaining relatively free of ash, a shower of which would begin to settle as soon as smaller wood became consumed. The ground would become smothered when supporting timber burnt through and allowed the main fuel-load to fill the space. Firing such a structure during prevailing axial wind of medium to high strength (say above 5m/s) would result in rapid generation of very high temperatures within the pyre under conditions of forced ventilation, sufficient to sustain the high levels of radiant baking required.

Such windier conditions, common now and during the Bronze Age, and which prevail at the majority of upland round barrows, located as they are in exposed locations, are sufficient to promote burning over central areas of the pyre-base to the same degree as seen at the margins of the pyre. Collection of cremated bone from a well-ventilated ash-bed, soon burnt out and reduced to a very small residue by wind-deflation is also easier than for a larger ash-choked bed, smouldering for a longer-period.

Selective use of greener timber in the frame of such a raised box-pyre would add to the efficiency of the cremation process by allowing delayed collapse and final combustion to follow an ordered sequence. As seen in experimental pyre 2, use of green timber for uprights would act to strengthen the corners of the burning frame, helping to prevent premature collapse. If, in addition, the lowest tiers, and especially any raised grate which they supported, were of similarly fresh timber, then sap would delay their burning, acting to keep basal ventilation open and the burning mass aloft until appropriately late in the process.

Comparative analysis: the ring-pyre The properties of the primary ring-pyre-base excavated at Guiting Power 1 round barrow, and details of a comparable experimental pyre are as follows (TABLE 12; FIGS 18,19). Data from experimental ring-pyres allow identification and further analysis of the example sealed under the centre of the round barrow at Guiting Power 1.

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experimental pyres TABLE 12: The ring-pyre-base at Guiting Power 1 round barrow (comparable to experimental PYRE 5) PROPERTY DATA -----------------------------------------------------------burnt crust shape and approximate width/length (m) visual circular: 3m diameter from MS circular: 4m diameter ?original pyre circular: 4m diameter thickness (max) 5cm ring pattern present, margins more burnt burnt plumes present, extending ?down-wind post holes absent pyre-debris depleted: ash-bed cleared of larger debris cremated remains adult: male in pit-scrape, over it, and within body of rubble cairn burial pit scrape cut into pyre-base oxidation of bone high finds associated flint core (burnt) and arrowhead fragment (unburnt) related structure none preservation base semi-cleared, trampled sealed under covering stone cairn date early 2nd millennium BC Key: crem(ated).

timbers sloping away. Some clearance accompanying construction activities over the centre, burial and encairnment, would cause localised depletion of magnetically enhanced sediment, contributing to the ring-like distribution of MS.

-size The original pyre was probably a conical stack, some 4m across at the base, with a fuel-load many times larger than used in the type of adult-sized box-pyre required for routine cremation. Its greater size, difference from the type of box-pyre in more routine use, and its firing just before construction of the round barrow began, suggest that it may have had a ceremonial as well as cremating function. The depth and intensity of burning indicate that the original blaze may have been prolonged by addition of further fuel to the fire, the event having something of a festive emphasis. Analysis of orientation of structures at the site suggests a possible interest in the westward horizon, perhaps linked with the solar-seasonal cycle, and such a large dedicatory conflagration, circular in plan, could perhaps have represented some form of solar mimicry.

-firing and the cremation process The extent of burning over the pyre-base indicates very intense and efficient combustion, sustained over a period of about a day or so. The strength of burning is also confirmed by highly oxidised bone in the primary cremated deposit. Deflation of the final ash-bed would have left relatively little debris to clear, with the cremated bone semi-exposed and easy to remove. Human bone would have been all but destroyed by a pyre of the observed intensity, and it is perhaps possible that the firing took place in two stages, although no indication of this survived in the pyre-base. Cremation in a smaller pyre, of ring- or box-type could have taken place at the centre, with ready retrieval of bone within 4-8 hours. The pyre could then have been re-kindled with additional timber, and continued to burn for a longer period, perhaps days, as other auxiliary rituals and preliminaries to establishment of the barrow took place.

-shape The burnt pyre-base shows a clear ring shape, the result of increased oxidation of sediment around its margins, visible despite subsequent burial and encairnment over the centre. The pattern of magnetic susceptibility (MS) over the pyre-base shows augmentation towards the E side, indicating increased down-wind burning under westerly wind, the prevailing direction in the area. That this enhanced ring developed suggests that the fuel-load may have been rather more steep-sided than conical, thereby allowing intensity of radiation to scorch surrounding surfaces more effectively than for

-grave-goods Again only the most resilient material was found, a lump of burnt flint, to suggest any placement of pyre-goods.

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experimental pyres interpretation of such sites, and discussion of their general function, for instance their status as ritual monuments of longer currency.

CONCLUSIONS -the utility of experimental data in identification of pyre sites Data from this series of experimental pyres enable fuller analysis of those ancient pyre-bases found sealed under Bronze Age round barrows, allowing clearer identification, and some inference as to original pyre-structure and conditions of firing. It has been possible to determine the ground-effects left by a unit box-pyre of adult size, of a type likely to have been in routine domestic use, and to recognise the former presence of such structures at test sites, and amongst other candidates which occur more widely in the archaeological record. Such pyre-sites survive as localised areas of burning, which occur as visual discoloration of sediment, often patchy and uncertain, supplemented by clearer, and more resilient areas of readily measurable magnetic enhancement.

On the experimental side, although many simulated cremations have been carried out, there is a distinct lack of a programmed approach to address obvious and readily addressable problems relating to the human remains. For instance, the relationship between position and condition of the corpse in the pyre and the resultant pattern of cremated residues in the ash-bed needs to be established, in replicate, to provide a basis for assessment of any surviving archaeological pyre-sites in terms of intactness and status of their residual bone. As a second example, the case for interpreting certain pyre sites as being of multiple- or single-use needs to be supported by data from repeated cremations on the same spot to determine ground-impact in terms of depth and spread of magnetically enhanced sediment.

-the need for quantified mapping of burnt sediment and key osteological data from replicate experimental pyres Although there is much archaeological information relevant to cremation-related activity, in terms of burial structures and osteology, there is a considerable lack of any attempt to map patterns of burning over associated surfaces and through stratified sediment in a quantified manner. Such data are essential for identification and interpretation of ephemeral structures such as pyre areas, of event-phasing represented by pit and other feature fills, and in discussion of funerary activities as indicated by other patterns of burning and scattering. Despite successful high-resolution mapping of burnt sediment, not only in visual terms but as increased magnetic susceptibility (MS), over the pre-mound surface at Guiting Power 1 round barrow, Glos. (Marshall 1998, 2007a; this paper FIGS 17-22) there still seems to be a distinct lack of application of these simple procedures elsewhere. For instance, availability of such MS data for those recently discovered candidate pyre sites and their settings shown in FIG 15 would have added greatly to their interpretation.

-the potential wealth of data The large number of cremated deposits which survive as later insertions within and around barrows, and in other non-monumental cemeteries, presuppose the existence of many parent pyre-sites. These known deposits must be a small fraction of the actual number of cremations which took place routinely over the centuries of the Bronze Age in southern Britain, as can be estimated from some appropriate value for the death-rate. This indicates that, even given repeat, superimposed cremation within approved cremation-grounds, the number of pyre-sites which exist should be high, despite problems of survival and erosion. Some means of identifying and assessing them where they do survive sufficiently, problematic though this will be in many cases, must be firmly based on quantitative data from experimentation.

Detailed experimental data are important in further characterising burnt features which are already more obvious candidates for pyre-bases, as suggested by deposition of human bone within them and post-structures around them. It is also essential in discussing other directly burnt areas, or those rich in scattered burnt debris, which have no such clear associations, or survive only as slight traces. Here, there may be an absence of any ground-fast post-structure suggesting a mortuary platform, or of any cremated deposit, which may have been otherwise utilised, or placed remotely, for instance as a secondary burial in a round barrow or nearby. Clearer identification of pyre- or fire-bases in and around round barrows is of direct interest to

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Parker-Pearson, M., Sharples, N., and Symonds, J. 2004. South Uist: archaeology and history of a Hebridean Island. Stroud: Tempus. Piontek, J. 1976. Proces kremacji i jego wplyw na morfologie kosci w swietle wynikow badan eksperymentalnych. (with summary in English). Archeologia Polski 21 (2), 247 ff. Warszawa-Krakow-Wroclaw.

Walker, P.L., Miller, K.W.P., and Richman, R. 2008. Time, temperature, and oxygen availability: an experimental study of the effects of environmental conditions on the color and organic content of cremated bone. In C.W. Schmidt, and S. Symes (eds.). The analysis of burned human remains. Elsevier Press. Chapter 7. pp. 129-136.

Rahtz, P. 1970. Excavations on Knighton Hill, Broad Chalke, 1959. Wiltshire Archaeological Magazine 65 part B, 74-88.

Wells, C. 1960. A study of cremation. Antiquity 34, 29-37.

Rieu, E.V. [translator].1978. Homer: The Iliad. Penguin Books.

Werner, A. 1990. Versuche zur Rekonstruktion provinzialrömischer Brandbestattungen vom Typ Bustum. Experimentelle Archäologie in Deutschland. Begleitschrift zu einer Ausstellung des staatlichen Museums für Naturkunde und vorgeschichte Oldenburg. Archäologishe Mitteilungen aus Nordwestdeutschland, Beiheft 4, 227–230.

Savory, H.N. 1949. Two middle Bronze Age palisade barrows at Letterston, Pembrokeshire. Archaeologia Cambrensis 100, 67-87. Schlenter, U. 1960. Brandbestattung und Seelenglauben. Verbreitung und Ursachen der Leichenverbrennung bei aussereuropäischen Völkern. Berlin.

Whittaker, C.R. 1969. (translator). Herodian: the Histories. London: Loeb.

Sheridan, A. 2009. Replicating an early Bronze Age cremation from Findhorn [Moray, Scotland] involving a faience necklace and other artefacts. Ancient cremation workshop, 10 Oct 2009. Osteoarchaeology Research Group, Cardiff University.

Wilkins, B. 2008. N6 Galway to Ballinasloe Scheme, Contract 2. Final Report on archaeological investigations at Site E2437, a Bronze Age cremation pyre and burnt mound in the townland of Newford, Co. Galway. Project code: NGB05. Unpublished report: Headland Archaeology, Ireland.

Sigvallius, B. 1994. Funeral Pyres. Iron Age Cremations in North Spånga. Theses and Papers in Osteology, 1. Stockholm, 15–32.

Williams, H. 2004. Death warmed up: the agency of bodies and bones in early Anglo-Saxon cremation rites. Journal of Material Science 9(3), 263-291.

Sorensen, T.F. 2009. The presence of the dead: cemeteries, cremation and the staging of non-place. Journal of Social Archaeology 9(1), 110-135.

Woodward, A. 2000. British barrows: a matter of life and death. Stroud: Tempus.

Troy, C. 2007. N6 Galway to Ballinasloe Scheme, Contract 2. Report on the human remains from Site A024/1, A Bronze Age cemetery and pyre in the townland of Newford, Co. Galway. Unpublished report: Headland Archaeology, Ireland.

Disclaimer The following paper contains unauthorised material relating to the programme of round barrow excavation and experimental pyre construction at Guiting Power:

Troy, C., Tourunen, A., and Stewart, K. 2010. Paying respects: the multi-disciplinary analysis of an early-middle Bronze Age cremation cemetery from Ballybar Lower, County Carlow. http://www.wac6.org/livesite/posters/poster_files/WA C_164_Troy_Tourenen_Stewart.pdf

McKinley, J.I. 1997. Bronze Age 'barrows' and funerary rites and rituals of cremation. Proceedings of the Prehistoric Society 63, 129-145.

Ubelaker, D.H. 1981. A replicative cremation experiment. North American Archaeologist 2(4), 275-283.

This paper contains in figs. 2 and 4 unauthorised publication of, and inaccurate copies from draft

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experimental pyres technical diagrams produced during a programme of experimental cremation directed by A.J. Marshall (AJM). This was done without the knowledge of and without permission from the author (AJM). These items were released on trust to the author of that paper as a basis for discussion, and still remained subject to full copyright restrictions. The pyre structure published in McKinley 1997, fig. 2 is based on that for pyre 1, given in Marshall FIG. 3, adapted to contain elements observed during operation of pyre 2 (see Marshall FIG 5). The fictional pyre structure shown in McKinley 1997, fig. 2 formed no part of the experimental programme, but is nevertheless matched with environmental data for pyre 1 (Marshall fig. 4).

Establishment, CRE Technical Services, Stoke Orchard, Cheltenham, Glos. GL52 4RZ (UK), who provided staff, and equipment, to help monitor environmental conditions at the pyres. The UK Weather Centre, Bracknell, Berkshire provided exact predictions of wind direction and intensity, which allowed pyres to be constructed with the correct alignment several days in advance. Dr Armin Scmidt (Department of Archaeological Sciences, University of Bradford, BD7 1DP) provided scans of magnetic susceptibility (MS) through sediment cores taken from the base of pyre 2. Dr Gerry McDonnel (University of Bradford), and Dr Peter Northover (University of Oxford) provided metal samples for inclusion in pyres and commented on their subsequent analysis.

Photographs of one of the experimental pyres (McKinley 1997, figs. 1, 3) were also taken by Ms McKinley, against express project policy, and without the knowledge of, or any permission from the director (AJM), or from the owner of the private land on which experiments took place. These photographs are unacceptably poor in quality, contain no essential scaling, and are misleading, in that they certainly do not represent the actual organisation at the site, nor the care taken with photographic recording. In addition, no permission was given to include any references to the programme of round barrow excavation, closely linked to the experiments, references which also contain errors. All experiments were entirely devised and carried out by AJM, with specific technical aid from the Environmental branch of the Coal Research Establishment (Stoke Orchard, Glos.), not jointly with Ms McKinley, as stated (p. 132), who was present on just two occasions as an observer.

The author is most grateful to Dr Mogens Bo Henricksen of the Odense Museum, Denmark, director of the Lejre-Hollufgarde programme of experimental cremation, for helpful discussion of the topic in general, and for very useful suggestions regarding the final version of the paper.

CAPTIONS FOR FIGURES COPYRIGHT The author, A.J. Marshall produced all of the figures and plates and is the copyright holder, unless otherwise stated. Where material from other sources has been used as a basis for figures this is acknowledged (after: [author, publication]). FIGURE 1 LOCATION of the experiments in the Gloucestershire Cotswolds (the Guiting Power area, SP 0924).

This publication was done without consulting AJM, contrary to statements made in Acknowledgements (McKinley 1997, 143). Representations to the editor of Proceedings of the Prehistoric Society, Dr. J. Gardiner, to prevent final publication, in breach of copyright, were ignored.

FIGURE 2 INTRODUCTION: suggested basic structures.

box-pyres:

FIGURE 3 PYRE 1: box-type, built using regular-cut timber/ the structural sequence during combustion.

Acknowledgement The project formed part of the programme of excavation sponsored by the Guiting Manor Amenity Trust, at the instigation of its founder, Mr. E.R. Cochrane.

FIGURE 4 PYRE 1: environmental conditions, and temperatures generated within the pyre. FIGURES 5 PYRE 2: box-type, built using natural timber/ the structural sequence during combustion.

Planning and direction of the project, all geophysical survey, recording, retrieval and extraction of samples, post-excavation analysis, including production of publication drawings and text, experimental work, additional survey, and investigation providing background for the project, were carried out entirely by the author.

FIGURE 6 PYRE 2: environmental conditions, and temperatures generated within the pyre. FIGURE 7 PROPERTIES OF PYRE-BASES: PYRES 1-2/ the pattern of burning over the underlying soil surface, viewed after clearance of loose pyre-debris.

Especial thanks are due to the Environmental Monitoring Section of the Coal Research

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experimental pyres FIGURE 8 PROPERTIES OF PYRE-BASES: PYRE 1: magnetic properties of the pyre-base, as measured after clearance of loose pyre debris. FIGURE 9 PROPERTIES OF PYRE-BASES: PYRE 2/ magnetic properties of the pyre-base, as measured after clearance of loose pyre-debris.

FIGURE 16 MATCHING EXPERIMENT WITH EXCAVATION: Guiting Power 1 round barrow (Glos.)/ the site-plan after complete excavation, showing the location of pyre-bases. FIGURE 17 MATCHING EXPERIMENT WITH EXCAVATION: Guiting Power 1 round barrow (Glos.)/ areas of burnt sediment within and around the barrow, as shown by magnetic susceptibility (MS) survey at 0.25m interval over excavated surfaces. Instrumentation: Bartington MS2/D-head. Data: after x2 low pass filtration, greyscale with black high, all units vMS (SI), displayed at 1 s.d. about the mean. a. 27-81; b. 16-65; c. 19-160; d. 24-141.

FIGURE 10 PROPERTIES OF PYRE-BASES: box-pyres of simple stack (PYRE 3), and log-edged type (PYRE 4)/ the pattern of burning over the underlying soil surface, viewed after clearance of loose pyre-debris. FIGURE 11 PROPERTIES OF PYRE-BASES: PYRE 5: ring-type/ the pattern of burning over the underlying soil surface, viewed after clearance of loose pyre-debris.

FIGURE 18 MATCHING EXPERIMENT WITH EXCAVATION: Guiting Power 1 round barrow (Glos.)/ the central ring-pyre.

FIGURE 12 PROPERTIES OF PYRE-BASES: PYRES 1-5/ magnetic properties of cleared pyre-bases, as shown by magnetic gradiometry and magnetic susceptibility (MS). Data: vMS (SI), after 2x2 low-pass filtration, and x2 x/y interpolation, greyscale with black high. a. 0.4 to 4.3 nT, using a Geoscan fluxgate gradiometer; b. 17-243 vMS units, using Bartington MS2/D-head; c. 12-249 vMS units, using Bartington MS2/D-head.

FIGURE 19 MATCHING EXPERIMENT WITH EXCAVATION: Guiting Power 1 round barrow (Glos.)/ analysis of the ring-pyre base using data from experimental cremation. FIGURE 20 MATCHING EXPERIMENT WITH EXCAVATION: Guiting Power 1 round barrow (Glos.)/ the satellite pyre, at the SE of the barrow area. FIGURE 21 MATCHING EXPERIMENT WITH EXCAVATION: Guiting Power 1 round barrow (Glos.)/ the secondary pyre, at the NW of the barrow area.

FIGURE 13 ANALYSIS: experimental box-pyres/ the general sequence during combustion. FIGURE 14 ANALYSIS: displacement during cremation of major skeletal elements from a prone corpse, as shown by the distribution of cremated bone in primary pyre-debris. Distribution of burnt bone over the ash-beds of: A: experimental pyres in this programme The summaries shown here indicate a degree of correspondence between the prone corpse on the pyre (surgically-modified sheep) and the resultant scatter of cremated bone in the undisturbed upper ash-bed. B: parallel/ the pyre area at Pencraig Hill (Lothian). A well-preserved pyre area within the Neolithic trapezoidal timber mortuary structure (shown inset at the right) produced a scatter of cremated human bone interpreted as originating from body parts rather than an intact articulated skeleton (data re-plotted after Duffy and MacGregor 2008, fig. 4).

FIGURE 22 MATCHING EXPERIMENT WITH EXCAVATION: Guiting Power 1 round barrow (Glos.)/ analysis of the satellite and secondary pyre-bases (box-pyres) using data from experimental cremation.

CAPTIONS FOR PLATES PLATE 1 Instrumentation for pyre 1. A: pyre fully-constructed and undergoing instrument checks before placement of the corpse, and ignition. The automatic weather-monitoring station can be seen in the background. B: thermocouples secured to upright metal pods within the body of the pyre. Scale (horizontal): 50cm. C: the weather station automatically logging temperature, humidity and wind direction.

FIGURE 15 PARALLELS: pyre structures under Bronze Age round barrows in Britain/ a selection of excavated examples. Balnaguard (after Mercer and Midgley 1997); Amesbury G71 (after: Christie 1967); Amesbury G61 (after: Ashbee 1985); Sproxton (after: Clay 1993); Brenig 40, 42 (after: Lynch et al. 1974); Letterston 2 (after: Savory 1949); Trelystan (after: Britnell 1982).

PLATE 2 PYRE 1: part of the range of unburnt copper-alloy items, before placement on the pyre to monitor survival rates, after firing, for a range of metal-shapes and sizes. Scale: 10cm.

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experimental pyres mass of fragmented, cremated bone (white), and soft-tissue residues (black) can be seen just to one side of the metal instrument pods, as accumulated in a relatively concentrated area over the mid-line.

PLATES 3a-3f PYRE 2: the combustion sequence, from initial construction to the cooled ash-bed of the burnt-out pyre. A: the pyre and platform under construction, with reserve fuel-wood visible in the background. Scale: 2m; B: the pyre fully constructed, with the corpse placed on the platform. Scale: 2m; C: the pyre 5 minutes after ignition, with the fire spreading into the upper front section; D: a detail of the upper part of the pyre fully alight after 20 minutes, with charring of the corpse penetrating the shroud and outer layers of the body; E: the pyre structure extensively burnt after 1 hour, the front section largely gone, with the charred timbers of sides and back remaining more intact as burning progressed inwards and upwards from the front ignition end. The corpse, reduced to burnt bone and charred soft tissues, sunk within the interior of the pyre, lay in the upper ash bed; F: the ash bed after 1 hour 45 minutes, with most of the fuel-wood burnt away, except around the basal margins, to form the ash bed, with highly cremated bone and soft tissue char in its upper layer;

PYRE 2: more detailed lateral views of the ash-bed and cremated remains visible in A. B: from the right; C: from the left. Details of cremated bone and charred tissue on the cooling ash-bed. D: PYRE 2: relatively intact ribs, vertebrae, and long bones are visible amongst the charred tissue residues. Scale: 20cm. E: PYRE 2: as D but with redundant thermocouple wires visible in the foreground; F: PYRE 1: concentration of bone including ribs, longbones, and vertebrae amongst charred tissue, with a scapula in the foreground; G: PYRE 1: a section of intact and articulated vertebrae. Scale: 10cm. PLATE 8: Ethnographic parallels A. Cremation on ghats in Nepal. A series of commercial cremations taking place on very compact pyres of stacked blocks shows a poorly-burning sequence from part-burnt in the background to the laying of a corpse in the foreground. Partly cremated corpses are probably destined for the adjacent river. Source and copyright: http://en.wikipedia.org/wiki/file:ghat_nepal.jpg

PLATE 4 PYRE 1: patterns of burning caused by the pyre over underlying sediment. A ring of radiant burning (redder) marks the margins of the central ash-bed, this latter lying within the impressions of the large, lateral, basal timbering. Scale: 50cm. PLATE 5: PYRE 2: patterns of burning caused by the pyre over underlying sediment. The less substantial and less regular pattern of burning caused by the lighter timber frame of this pyre contrasts with the more intense ground-effects of pyre 1. Scale: 50cm.

B. Pyre at Pashupatinath Temple, Kathmandu, the most widely used place of cremation in Nepal. A well burning pyre perched on basal blocks has adequate fuel for effective cremation of the corpse. Source and copyright: http://en.wikipedia.org/wiki/File:Pashupatinath_Tem ple_cremation.jpg

PLATE 6: PYRE 1: stratigraphy of burning caused by the pyre over underlying sediment. A: the pyre-base excavated in opposite quadrants. Scale 50cm. B: a detail of the section through the pyre-base showing shallow penetration of visibly burnt sediment within the upper few centimetres of the natural clay surface. Scale (horizontal): 20cm, (vertical): 10cm.

C. Ubud cremation: Hindu rite, Bali, Indonesia. Efficient cremation is taking place in an elevated position on an elaborately decorated pyre-structure. Source and copyright: http://en.wikipedia.org/wiki/file:ubud_cremation_ 1.jpg D. Imperial pyre or mausoleum structures shown on Roman coins. If these issues depict the pyre (rogus) rather than the stone mausoleum (ustrinum) then the elaborately decorated, multi-tiered structure contained the corpse in the second level of a timber frame internally stacked with fuel-wood. Source and copyright: [email protected]

PLATE 7 The ash bed with cremated bone and tissue in its upper layer. A: PYRE 2: the near-final ash-bed, after 1 hour 45 minutes. The ash bed is viewed from the ignition end, the basal course of the pyre and two uprights for the platform heavily charred but still in situ, with the metal pods for thermocouples visible. The smouldering

Reverses of silver denarii commemorate: upper: Lucius Verus, after 169AD;

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lower: Marcus Aurelius, c180AD.

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experimental Iron Age grain storage

PAPER 2 Methods of grain storage during the Iron Age in southern Britain: further investigation by experiment ABSTRACT Discovery of unusually large, rock-cut 'silo-pits' at certain Iron Age enclosures in the Cotswolds (Gloucestershire, UK), with parallels elsewhere, prompted examination of their potential as unsealed but roofed granaries, in view of practical difficulties inherent in sealing them at ground level and other structural evidence. A series of fully-monitored experiments allows their performance during over-winter storage of grain to be assessed, and compared with operation of smaller sealed pits. Data quantify environmental conditions and the changing state of stored grain, indicating that such roofed silo-pits are in fact more effective for grain storage than sealed pits, with access to stocks conferring many additional practical advantages. Evidence for the function of such pits is briefly reviewed, with grain storage considered the most common primary function for pits of defined type. Assemblages of pits from various sites are analysed briefly, and key statistics established as a basis for discussion of their properties for grain storage. Spatial patterns within pit clusters are discussed, with the simpler, attenuated distributions at smaller settlement sites used as a key for understanding more complex, crowded storage areas at larger sites. A basic ergonomic model for grain production is presented to provide a closer context for the particular system of storage proposed here. Use of alternative methods for grain storage is suggested during the Iron Age in southern Britain, providing appropriate access to stocks. Smaller, sealed pits are proposed for seed-grain, with food grain variously stored in larger sealed pits, and significant stocks held in pits with accessible superstructures, some of large silo-type. Above-ground storage is briefly discussed in relation to pit-based storage. The advantages of such diversity of storage are outlined, and reasons sought for widespread use of pit storage during the Iron Age, as opposed to earlier and later periods, with emphasis on the need for security. The influence of changing climate on the choice of method is also considered. Keywords: Iron Age, settlement, agriculture, storage pits, experimental archaeology. although circular in plan, these Neolithic pits are shallow, with average diameter 70cm and depth 23cm, are generally truncated to an unknown degree, and are of a form which seems entirely unsuitable for grain storage. Little or no other structure remains at this site, and such pits remain of unknown function, but were infilled with quasi-domestic debris from phases of possibly temporary occupation or other activity, of varying duration.

Section 1: CONTEXT INTRODUCTION If operational issues relating to grain storage during the Iron Age in general are to be analysed, then the evidence for this being the principal purpose of the pits in question must be reviewed briefly. The case for interpretation of the majority of typical Iron Age pits, those over a certain minimum volume (FIGS 12-13, 14a), for grain storage, although not clearly proven from the archaeological record, seems highly persuasive, for a range of reasons, related to historical evidence, ethnographic parallels, and practical, functional considerations.

The case for grain storage as the prime function for pits -classical authors Grain storage was a topic covered by several Greek and Roman authors, writing on agricultural practices in the Mediterranean world and to a lesser extent amongst the Celts settled beyond it. Such sources clearly establish the currency of subterranean storage, in addition to above-ground grain reserves. However, much of the information is unlikely to be based on first-hand observation, with reuse of existing documentary sources probable, and may be regarded as far less reliable for marginal areas of northern and western Europe than for southern. These authors were also writing towards the end of the Iron Age, when use of pits may have been in

These Iron Age pits differ in form and capacity from the majority of those which are earlier, as if a fairly specific format had developed to cope with the storage needs of more intensive arable agriculture. In contrast, Neolithic and Bronze Age pits tend to be shallower, more variable in form, and very unlike those of typical Iron Age type (Allen et al. 1993; Lambrick and Allen 2004, fig. 2.4). The difference between pits of Neolithic date, and those of the Iron Age is well demonstrated by the 236 examples excavated at Kilverstone, Norfolk (Garrow et al. 2005). In contrast to the typical Iron Age pit,

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experimental Iron Age grain storage shelter, and stored produce (Mattingley 1948).

decline for grain storage. Although there is repeated reference to pit storage of grain, there is little detail on the precise conditions of operation, and nothing closely relevant to their use as unsealed but covered repositories, the main subject of this paper. A selection of sources are as follows:

The reliability of all such information, and its relevance to grain storage remains uncertain. It may, however, highlight the need to maintain security of stored produce underground, a topic returned to later in this general analysis.

..Marcus Terentius Varro (Varro Reatinus), 116-?27 BC, mentions pit-storage within the Mediterranean area in his Rerum rusticarum de agricultura, Books 1-3 (Hooper and Ash 1934).

-ethnography Use of pits for storage of various products has been noted widely, with examples from Europe (Romania, Hungary, Balkans), North America (Omaha Indians), Africa, and Australasia (Maoris), many operating in damp, temperate environments similar to that of Western Europe. Stored items include grain, protective linings are sometimes used, pit forms include similar utilitarian types found in Iron Age European contexts, and both outdoor sealed, and indoor lidded examples can be cited (Ellison and Drewett 1971; Evans 1982).

..Diodorus Siculus, c. 90 to 21 BC, floruit c. 49 BC, travelled in Asia and Europe compiling his Bibliotheca Historica, Books 4-6 of which deal with Greece and Europe (Oldfather 1946). Much of this narrative consists of compilation, drawing on now lost works, but supplies certain interesting detail. For instance, like Strabo he quotes Pytheas, through Poseidonius, both making similar references to Britons, saying that they 'cut off the ears of grain, and store them in houses that are roofed over, and pluck the ears from day to day'.

..North America Amongst the wealth of ethnographic parallels for pit storage, those from amongst native North American cultures of the Mid-West are particularly interesting, and appear relevant to discussion of pit use in Iron Age Britain, providing combined data from archaeological and historical sources. These modern agricultural groups are sufficiently similar in key aspects of their arable economy, subsistence strategies, and physical environment to those of Iron Age Britain to allow very generalised comparisons to be made. Data exist for groups in the more arid American South-West, such as the Hidatsa (Wilson 1987) and Mogollon (Sturtevant 1981-1996), and for those in the wetter, colder Mid-West, such as the Ioway (Blaine 1979) and Oneota (Harvey 1979; Martinek 1999). The latter faced similar practical environmental problems in their use of pit-based storage of cereals and other foodstuffs to those envisaged for the farmers of Iron Age southern Britain.

..Strabo, c. 64/63 BC to c. 23 AD, compiled a Geography, written during the reign of Augustus (27 BC to 14 AD), which covers peoples and countries known to the Greeks and Romans (Jones 1917-32). In the section on Britain, Ireland and 'Thule' he mentions the inclemency of the weather, and the existence of large store-houses for grain, but includes little of direct use to detailed consideration of agronomy. ..Gaius Plinius Secundus, 23 to 79 AD, published Historia Naturalis around 77 AD, Book 18 of which contains significant detail on cultivation of grain in the Mediterranean area (Bostock and Riley 1856). In discussing methods of storing grain, he describes purpose-built granaries built above-ground, together with details of appropriate construction and orientation, and matters relating to the resilience of stored grains and other seeds. He then continues with a consideration of ground-based storage, drawn from drier Mediterranean Europe:

The Mogollon were desert pit house-dwellers, with a developed agriculture, who stored food in bowl-, to barrel-shaped pits located both inside, and outside houses. The floors of larger pits were covered with timber, and pit-tops were capped with flat stones. Larger interior pits could be reused for burial (Sturtevant 1981-1996).

'The best plan, however, is to lay it [the grain] up in trenches, called 'siri', as they do in Cappadocia, Thracia, Spain and Africa. Particular care is taken to dig these trenches in a dry soil, and a layer of chaff is then placed at the bottom, the grain, too, is always stored in the ear. In this case, if no air is allowed to penetrate the corn, we may rest assured that no noxious insects will ever breed in it. Varro says, [Rer. Rust. de Agric. i, 57] that wheat, if thus stored, will keep as long as 50 years, and millet a hundred.'

The Oneota of the upper Missouri were Plains Indians, active 1000-1650 AD, who over-wintered grain in generally unlined storage pits of basin-, belland cylindrical form, averaging 1m wide and 1-1.5m deep, with larger examples known. Excavated pits have been used as the basis for modern storage experiments, entirely successful in outcome, with dry and cool conditions considered the key criteria (Martinek 1999).

..Publius Cornelius Tacitus, c. 55 to c. 120 AD, refers in his Germania (chapter 16, section 4) to native use of underground chambers, camouflaged by debris, in which they took temporary winter

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experimental Iron Age grain storage challenging: the average year-round temperature is about 28oC, rainfall 0.5-1m, and the area has a 3-month rainy season.

Actual use of storage pits has been recorded amongst the Hidatsa, as outlined by native informants, who used bell-shaped pits for storage of maize, dried squash, sunflower seeds, and beans. Some of these pits were '4-5 feet' deep, with larger pits requiring ladders (Wilson 1987). Pits were floored with dry twigs, lined and covered with dry bundled grass, and when full were covered with short sections of log, topped with a thick layer of wood-ash, then earth (FIG 15a). Pits were left entirely unmarked, as protection against raiding Sioux, clearly indicating that added security was an issue in choice of pit-based storage.

above-ground: Most structures are not proofed against moisture, rodents or air, and structural defects develop in the roof, walls, and support columns. mud rhombus: this has a cylindrical body of clay-grass plaster, is raised on a circular timber-legged support, and capped with a conical thatched roof through which 1-8 tonnes can be loaded. Storage for 6 months to 3 years can result in losses of 10-20%.

..Africa Northern and central Africa provides another source of ethnographic information on pit storage of cereals amongst farming communities, a method which is still in widespread use, and with ancient examples establishing a long tradition.

thatched rhombus: a woven grass cylinder or sphere, constrained with tension bands around its girth and with a ring of timbers supporting its upper margin, holding 0.5-8 tonnes, is raised on a wooden platform, and capped by a conical thatched roof. Losses are similar to those for the rhombus.

There are examples of modern use of pits for grain or water storage in Morocco, with many pits lined, and grain losses noted as high (Bartali 1987).

in-hut earthen pot: storage pots hold 5-20kg of threshed cereal, used mainly as seed-corn.

In Chad, pits for storage of sorghum and guinea corn are of two main types. One is bell-shaped with a large chamber and small entrance, which can be further constricted by a clay rim acting as a foot-rest. The other is cylindrical with a wide opening, its walls supported by mats, and when not covered it can be surrounded with thorn bush branches for protection from animals (Gronenborn 2010). The antiquity of pit storage in this area is shown by an excavated example of the type with constricted opening. A conical, flask-shaped pit (FIG 15a) with narrow upper entrance shaft, 1.2m diameter at the base and originally about 1.7m deep, possibly for storage of plant food such as grasses or early cereal domesticates, dated 1500-1200 BC, was cut through a clay layer into drier sand (Gronenborn 1997). Modern examples of this type are unlined, and when full the base of the entrance shaft is covered with straw matting then filled with clay. In sealed use, build-up of moisture is minimal and low oxygen levels are maintained. Once unsealed the pit is completely emptied and not reused. The largest pits contain about 2 tonnes. Cylindrical pits are lined and then sealed over. The location of pits is disguised in times of trouble.

subterranean: Pits are cylindrical or square in plan, 1-3m across and deep, usually straw-lined, hold 1-6 tonnes, and are constructed only in areas where the water-table is low. Full pits are covered with timbers and soil, and can be left sealed for 1-5 years, but once opened they are fully emptied. The same pit can be used for up to 12 years, with annual maintenance by cleaning and replacement of the lining. Losses are similar to those for the rhombus. Testing of experimental linings for pits storing sorghum in the central clay plain of the Sudan demonstrated the usual problems of marginal spoilage caused by incoming dampness at the sides and base, with only a slight improvement in using chaff lining over mud-dung plaster (Abdaklla et al. 2001). The predominant practice of sealing pits is clearly seen in the ethnographic record, with far fewer examples of accessible covered pits. The cylindrical pit is fairly ubiquitous, and the more constricted flask-shaped pit has a wide currency, with well-separated examples from the Sudan, southern Britain, and North America suggesting convergent evolution of structures to solve a common problem (FIG 15). The balance between above-ground and subterranean storage also varies, with the former often dominant, as can be seen in different parts of Nigeria and the Sudan. There is also fairly broad variation in the lifetime of pits, from single use to serial refurbishment being recorded. Also the most common practice seems to be that of emptying a pit

Traditional grain storage practices in the savannah of the Nigerian Sudan have been well documented, predominantly involving above-ground granaries but also including pits (Adejumo and Raji 2007). Millet, sorghum, maize, and cow-pea are usually stored in threshed condition, but often remain unthreshed. There are four traditional methods of storage, with structures incorporating local timber, straw, and mud-plaster. Storage conditions can be

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experimental Iron Age grain storage completely once opened, with no intermediate covering stage.

may have served as cool-stores for a variety of foodstuffs.

The variable nature of current and traditional storage practice should be borne in mind in interpreting archaeological storage structures, especially under the wetter ground conditions of the British examples central to the current discussion. There is certainly some evidence here, albeit indirect, for pit covering structures, and the experimental evidence presented in this paper proves ventilated pit storage as a superior method with many practical advantages over sealing.

At Gravelly Guy there was no direct evidence for use, but one pit was clay-lined and lay adjacent to a hut, perhaps acting as a water-butt, drip-filled from the eaves. Here too, some small bowl-shaped pits may have stored reserves of non-local clay (Lambrick and Allen 2004). Finds of carbonised grain within pits do not provide direct evidence for grain storage, since these deposits could have come from any external, grain-related activity. The fact that such surviving grain had been heat-treated would anyway render it far less suitable for pit storage in the first place, certainly as seed-corn. However, such deposits could provide indirect support for grain storage, if they were deliberate ritual offerings, made to mark success in the gathering and over-wintering of the harvest.

-ecology of sites In the southern British context, association between pits and storage of grain is indirectly suggested by their apparent absence at Iron Age sites which are inappropriately located for nearby arable cultivation. Sites with few pits, as on poor soils (Hardy and Cropper 1999), or in vulnerable locations, such as on the upper Thames flood-plain, at such settlements as Mingies Ditch and Watkins Farm, may have had a more specialist pastoral economy (Lambrick and Robinson 1979; Allen 1990; Allen and Robinson 1993). By contrast, those settlements on the more elevated, drier gravel terraces flanking the Thames, better suited for cereal cultivation and below-ground storage, produce an abundance of pits, as at Gravelly Guy (Lambrick and Allen 2004, fig. 1.4) and Wyndyke Furlong (Muir and Roberts 1999). Some sites in intermediate locations, such as Claydon Pike, producing few pits, may have relied on above ground granaries, as suggested by the presence of 4-post structures (Miles et al. 2007).

At Danebury, 33 such pits contained basal layers of carbonised grain. One pit contained a basal layer of carbonised grain overlain by ash, with the distinct possibility that the entire lower part was full of grain when abandoned. However, this could still be dumped refuse, since it would be difficult to burn grain effectively if confined within a pit bottom. In addition, the stratification of some pits indicate that they may well have contained a depth of unspecified organic material on abandonment, subsequent rotting and compaction of which caused slumping (Cunliffe 1984; Cunliffe and Poole 1991, p. 161). Several pits at Wyndyke Furlong also contained small amounts of carbonised grain and chaff (Muir and Roberts 1999).

-alternative functions Besides grain storage, many other functions have been suggested for pits (Reynolds 1976, 1979; Ellison and Drewett 1971; Evans 1982; Thomas 2005) either in primary use, or secondary reuse. These include storage of non-grain foodstuffs, salting meat, production of silage, water storage, latrine-related use, tanning of leather, dyeing, clay storage and refinement for pottery manufacture, and as a cache for weaponry. Although many of these uses, by their very nature, would leave little or no trace in the archaeological record, there is evidence for the latter two, clay residues remaining within atypical pits, as at Danebury hillfort, Hants. (Cunliffe 1984), and sling stones in pits at Maiden Castle, Dorset (Wheeler 1943).

If not primarily for bulk storage of grain, then it is difficult to suggest an alternative primary function for the majority of such pits, common on Iron Age sites in southern Britain producing clear evidence for active arable agriculture. The model of grain storage included in this paper certainly produces realistic results if pits are assumed to be essentially for this purpose.

The variety of size and shape of pits at Danebury suggests a range of designs to cope with different storage needs, although the majority of circular pits were considered likely to have been used for grain (Cunliffe and Poole 1991, p.161). Alternatively, sub-rectangular pits with large mouths, not easily sealed, and which frequently occur within buildings,

Even given storage of grain as a principal function, variety of size and form amongst pits suggests a range of more precise applications: capacities vary upwards from less than 1m3 to beyond 20, and forms change from cylindrical to flask-shaped. For instance, division of types between smaller pits for routine agrarian use and larger silos for centralised

The common presence rodent bones on pit-bases, and cases of claw-marks on pit walls, do not clarify the nature of the contents, since these could relate to any period of use or abandonment (Cunliffe and Poole 1991, p. 161).

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experimental Iron Age grain storage post-built granary, of the type reconstructed at Butser Ancient Farm (Butser 2010). It would allow regular access for inspection of quality and remaining quantity, any servicing of the storage area, and periodic removal of grain for consumption. A convincing reason must therefore be sought for any seemingly perverse use of sealed, underground storage, under damper, more adverse, less predictable conditions, not amenable to regular inspection and access, and with loss of at least a 5% proportion guaranteed from marginal rotting and general spoilage.

storage is suggested by examples in central Anatolia, in use during the 1st and 2nd millennia BC (Fairbairn and Omura 2005). Here, small and numerous pits, in regular domestic use over a long time-span, were possibly used for seed-corn or trade-grain, and are similar in form to those from the British Iron Age. Far larger pits, greater than 7m in diameter, of a type mentioned in Hittite texts, some excavated examples containing cereal remains, were confined to the Hittite period, and may indicate centralised control of grain supply. The date of storage pits Storage-type pits have a wide currency amongst agrarian communities both in time, Neolithic to modern, and in space, including Africa, America, the near East, and Europe, as a common response to the problem of securing bulk reserves. Amongst earlier archaeological examples, a flask-shaped pit from Nigeria has been dated 1500-1200BC (Gronenborn 1997), and pits from Anatolia of the 1st and 2nd millennia BC show clear differentiation of types (Fairbairn and Omura 2005).

The inherent efficacy of entirely above-ground storage seems self-evident. Even for pit-based storage, the experimentation at Guiting Power clearly demonstrates that unsealed pits, transitional between above-ground and subterranean options perform better than do fully sealed pits. This intermediate form includes many joint advantages, hence providing a practical compromise, as long as contents are kept dry from rain, and cool, which are primary, critical conditions not difficult to provide. There seems little inherent need to bother with pit-based storage at all, except perhaps for reasons of security, protection of contents against accidental fire-damage, or even perhaps to fulfil some ritual preoccupation. Even then perhaps only undertaking it as part of distributed storage of the harvest, with a range of structures spreading the risk to stocks.

The Iron Age pits from southern Britain, representatives of those mentioned by Roman writers on Celtic affairs, and which are the subject of this analysis, form a block of intermediate date. There is a peak of usage from about 350BC to 50BC, with relatively few comparable examples of Roman date to indicate any general continuity of practice. In more recent times, rare cases of survival in medieval Europe can be cited. Examples in Slovenia, some of which may have been for grain storage, have been dated from late 11th to mid 12th century AD (Milan et al. 2008). Another example from Scotland, cylindrical, stone and clay lined, 3.5m in diameter and 2.25m deep, containing carbonised oats in the fill, appears to have fallen into disuse only during the 16th century AD (Shepherd and Shepherd 1989). Further medieval and modern examples are given in Reynolds 1974.

Any interpretation of sealed pits as providing the best option for grain storage during the Iron Age must also explain why such structures are not prominent during the preceding Neolithic to Bronze Age, or even widely present during the succeeding Roman and medieval periods, when the requirement for viable storage of seed- and food-grain was no less critical for the population. Even during the Iron Age, pits of this type are not found in all areas of Europe. It is surely not the case that Iron Age farmers could not have constructed sufficiently robust, clay-caulked, timber and wattle hoppers for grain, either in purpose-built granary-huts, or within domestic round-houses. Here, grain would have remained entirely dry, cool, ventilated, viable, edible, accessible, closely supervised, and could be checked routinely for quantity, condition, predation, or infestation. Interpretation of rectangular post settings as stand-alone granaries presupposes that such grain-hoppers could be installed and operated successfully under exposed and testing weather conditions. The weight exerted by several tonnes of grain at the sides and over the base of any receptacle need not present any insuperable problems for construction. Splitting of grain into 1 tonne hoppers, or less, would reduce this factor even further, and furthermore such dispersed storage would act to add

In addition to examples from the ethnographic record, outlined in more detail elsewhere in this paper, pit-based storage of grain is also modern practice. For instance, storage of grain for up to 10 years as a reserve of stock-feed against drought years is frequent practice in Australia, given a well-drained site above the water-table and with the immediate surroundings graded to shed rain. Here pits are greater than 3m wide, lined and capped with plastic and kept gas-tight to deter insects (Andrews and Jensen 2005). A paradox: why store grain in damp underground conditions at all? There seem to be obvious advantages in maintaining bulk grain for long periods in dry, above-ground conditions, as for instance in a weather-proofed

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experimental Iron Age grain storage conflict. Under such threat, the essential unpredictability of unmonitored underground storage, and the inevitable losses of grain involved, would have been an acceptable insurance premium.

security to reserves. Even in operation of an entirely pit-based storage system, the need for some sort of above-ground storage buffer has been suggested by Reynolds (1974), arising from obvious problems created by routine broaching of a large pit, and having to remove the contents rapidly to safety. The existence of large storage jars on Iron Age sites has also been related to such storage needs, and other lined containers suggested, but only on a small-scale and temporary basis, with the pit still forming the mainstay of the storage system. It has also been suggested that 4- and 6- post structures may have formed granaries for grain, not in bulk, but in containers (Reynolds 1974; Fowler 1983; Whittle 1984).

If well camouflaged, there would be further advantages to placing storage pits outside the defended enclosure, where they would be even more difficult to locate by intruders, and would not take up valuable living-space. There are many such cases of extra-mural pit clusters which lie outside hillforts and settlement enclosures. Examples of flask-shaped pits, with constricted openings which were easily blocked, covered, and deliberately camouflaged, are recorded amongst the Hidatsa of North America (Wilson 1987), and can still be seen in the Chad basin of Nigeria (Gronenborn 2010) (FIG 15).

Relative impracticality could be suggested for many of the other widespread ethnographic and historic examples of pit storage for dry-goods such as grain, especially those in colder areas of higher rainfall, which present more of a challenge: but such storage did take place. Since there appear to be inherently better methods of storage for such unstable produce, secondary reasons must therefore be suggested to account for the relatively transitory phenomenon of pit storage, by common consensus mainly for grain, over the period of a few centuries in Iron Age Britain. It has been proposed that more secure storage in pits of a small fraction of the grain as seed-corn, whilst the bulk of the harvest remained potentially vulnerable as food-grain in above-ground structures makes little logistical sense (Cunliffe and Poole 1991, p. 162). However, the existence of a range of suitably small and larger pits at many sites suggests that both types of grain may have been sealed below ground, as well as in accessible pits, or fully above ground. Diversity of storage seems the best strategy for improved security of stocks.

If underground grain storage was encouraged by external threat to reserves then, as these social and economic pressures increased during the Iron Age, this might be reflected in the archaeological record by an increase in pit numbers, mean pit volumes, total volumes stored in pits, and in the greater importance of pit storage relative to suggested above-ground granaries. However, this appears not to be the case at Danebury where, over the entire period of occupation, total underground storage capacity seems to decrease, and the relative importance of pits in comparison to candidate above-ground granaries seems to wane, if indeed these post structures do represent granaries, a fact far from proven. By contrast, at Gussage All Saints, pit numbers do appear to increase over time. Here, pits also get larger and total underground storage increases, with the relative importance of pits as against putative above-ground granaries also increasing. The general situation on these and other sites is not therefore very clear or consistent.

-provision of additional security for at least part of the grain reserve may be highly important As the Iron Age progressed, increasing density of settlement and fortification of sites indicate a heavily exploited environment, with available space and resources under some pressure from growing population. Security of essential resources such as grain must have been a priority, even within defended hillfort interiors, not immune from raiding, nor from self-inflicted fire damage. If at least part of the grain reserves, both for seed and food, was sealed in pits, capped, and well camouflaged, then it could remain secure and undetected, whilst other deposits, in more obvious locations, were pillaged or destroyed. Destruction of grain reserves, and especially of seed-corn for the coming season would have been a major blow for any community, and would have formed a powerful tactic in any serious

-selective storage of essential seed-corn underground, and bulk food-grain above The range of pit sizes and shapes in use during the Iron Age (FIGS 12-14) suggests that they may have catered for a variety of storage requirements: of different durations, for different purposes, for divided ownership, and allowing different degrees of access to contents. Smaller pits could have been easily and efficiently sealed, and splitting any fraction of the grain, for future use as seed or as food between such smaller pits would provide some insurance against spoilage or theft of contents. The relatively small proportion of grain kept back for seed-corn would require smaller pits than for the bulk, allocated for food-grain or perhaps for trade. Division and storage of the harvest in the ratio of, for instance, 1 of seed to 4 of food might tend to produce pits of two main sizes, perhaps in this approximate ratio of

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experimental Iron Age grain storage That these repositories may have existed is based on the widespread occurrence of fairly standard types of rectangular 4-and 6-post settings at Iron Age sites. These could have supported a range of structures, including granary-sheds, but with alternative options remaining open, such as use for huts, rick-stands, or sheds (Stanford 1970, appendix pp. 125-126; Ellison and Drewett 1971; Reynolds 1972; Coles 1973; Wainwright 1979; Gent 1983, figs. 2 and 4; Cunliffe 1984; Cunliffe and Poole 1991). Reynolds (1999, p. 159) notes that interpretation of 4-post structures as overhead granaries is very poorly founded, and that they could indeed represent anything from sheds to watchtowers.

volumes. Such a grouping might be visible within data from samples of pits from archaeological sites, despite many complicating factors such as diversity of use, or recutting of pits for reuse. Many of the larger pits from archaeological sites seem too wide for easy and reliable sealing with a flat cover against external weather, for instance those examples wider than 1.5-2m in FIG 15b. This immediately suggests a different practice to that adopted for smaller, more easily sealed pits. These larger pits may have been intended for food-grain, requiring repeated access and hence remaining unsealed under covering structures, the pit also being of more open form to encourage ventilation, an idea assessed by the experimentation at Guiting Power presented in this paper.

The ground-plans of about 500 rectilinear post-built structures excavated at Danebury, many of which were distributed along internal roads, suggest they supported readily accessible, multi-level, general-purpose storage or workshop units. Some of these may have been used as ventilated, weather-proof, above-ground granaries, either as temporary holding for semi-processed grain, or as final storage after threshing and cleaning (Cunliffe and Poole 1991: pp. 104-140, figs. 4.64-4.66). Chronological data suggest that the smaller, simpler, less robust structures tend to be early and larger ones later in the sequence at the site, as noted for pits, but with all types occurring in all phases.

-changing climatic conditions may require additional safety of storage Any significant change in weather conditions would have required a reassessment of storage strategy (Gent 1983; Fowler 1983). It seems reasonable to suggest that increased rainfall would perhaps have encouraged storage in improved above-ground granaries, despite their higher exposure, with drier conditions and lower water-tables perhaps allowing more widespread subterranean storage. Drier summers and autumns would certainly render grain more stable for pit storage, in terms of reduced moisture content and increased dormancy. However, the archaeological and environmental data from the Iron Age suggest the opposite link: between increased pit storage and deteriorating climage.

The commonest type at Danebury, the small 4-poster of type E, has a mean side of 2.4m, which represents about 5.8 m2 of floor area (Cunliffe and Poole 1991). Although no superstructure has survived, given a notional 0.8m from the ground up to a raised floor, and then 1.5m headroom in a first storey, this resulting in a practical length for uprights of about 2.5m, each cubicle would have a storage capacity of about 8.6m3. Given accumulation of about 500 comparable structures, a 10-year lifespan for each, and occupation of the site for 450 years, then on average about 10 would have been open at any one time, giving an annual storage capacity of about 86m3, equivalent to about 52 tonnes of grain (see conversion factor given in 'A model for grain storage'. If only half of these timber structures were in fact used for grain this still represents considerable reserve storage.

Problems for interpretation -single use, or multiple reuse of pits Pits could be reused, either remaining essentially in original form with minimal cleaning, especially if relined, or in progressively enlarged form after partial or total recutting of surfaces. Pits at Danebury appear to show little obvious sign of the type of wear associated with reuse. However, about a third of the pit walls do bear tool-marks, but whether these indicate the relatively uneroded surface of the first and only pit, or one of a re-cut series of reused versions is not known (Cunliffe and Poole 1991: p. 161; plate 54/ p. 276; data on fiche 24, F5-F8). If there was no reuse of pits then the estimate of grain stored would have to be drastically reduced, and this can be done by alteration of variables in the simple storage model presented in this paper, where pits are given a 5-10 year lifespan.

The relative proportions of each of these structures can be shown to change over time at Iron Age sites where sufficient dating evidence exists. For example, at Danebury (Cunliffe 1984, table 100), the largest and best-dated sample, analysis suggests that use of pits appears to decrease over time, as granary-type post-structures increase (TABLE 1).

-subterrranean and above-ground storage: pits and 4-post structures (TABLE 1) Any discussion of function and operating conditions for grain storage pits must take into account their relationship with a second type of proposed granary structure, post-built, and located above ground.

However, the reverse situation is seen at Gussage All Saints (Wainwright 1979, fig. 113), where post structures were common in phases 1 (c. 500 BC) and

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experimental Iron Age grain storage 2 (c. 300 BC), but pits were increasing by phase 3 (c. 300 BC to c. 150 AD).

site, with several perhaps grouped. There is no direct evidence for function, but similarity of structure might suggest common use (Lambrick and Allen 2004).

At Gravelly Guy, the sixteen 4-post structures, all of possible early Iron Age date, are scattered over the

TABLE 1: Pits and post-structures at Danebury (Cunliffe 1984; Cunliffe and Poole 1991). Danebury periods

date BC

1-3, 4-5 6-7

550-400 400-300

all

potential grain storage capacity (m3) pits post strucs. total 538 368 906 173 639 812

ratio pits: post strucs. 0.7 3.7

711

1.4

1007

1718

use, could also act to transform overhanging or vertical walls to a more open profile, especially in softer, more friable rock, or gravel.

PROPERTIES OF IRON AGE PITS To provide background for the experimentation at Guiting Power the general properties of pits can be briefly reviewed as follows, using examples from groups at key sites in southern Britain.

-types of pit and their currency Excavation of the Iron Age enclosure at Little Woodbury (Bersu 1940) produced a range of some 190 pits, and allowed classification into six main types (FIG 14b), of which four are commonly encountered on Iron Age sites, and considered suitable for storage: type C ('cylindrical'), type D ('conical'), type E ('beehive'), and type F 'barrel'). At other sites, such as Danebury and Gravelly Guy, this system has been modified somewhat, but retains basic elements of Bersu's system.

Danebury hillfort (Hants.) has provided a large sample of pits, with 2399 located, of which 1707 (71%) have been excavated (Cunliffe and Poole 1991, 153-162). This sample provides a robust set of data on size, form, and patterns of use through time, against which those from other sites can be compared. Gravelly Guy (Oxon.) also provides a large sample (Lambrick and Allen 2004). Many other sites provide smaller samples, as at Little Woodbury (Bersu 1940), Conderton Camp (Thomas 2005), and The Park-Bowsings (Marshall 2007).

The narrowing neck of some conical pits has been seen as rendering their sealing more effective, reducing decomposition of grain at the pit margins (Reynolds 1974), and where mouths are much constricted this would certainly make camouflaging for purposes of security more effective (FIG 15a).

Capacity of pits (FIGS 10-14) Pits range from about 0.5 to over 10m3, with maxima of volume frequently lying between 1 and 2m3. A minimum volume for grain-storage pits of around 0.7-1m3 seems reasonable on practical grounds. Larger pits are more efficient for storage because an increase in pit size reduces the area of grain exposed to damp rock walls relative to the volume stored, reducing the relative loss from decomposition at the walls. The potential of pits to ventilate also changes with volume and shape, factors discussed in the section 'Basic statistics used for analysis of pit groups', under venting factor V.

Analysis of pits excavated at the following sites suggests no general preference for shape, although certain forms are more in evidence at individual sites, such as 'beehive' at Danebury and cylindrical at The Park-Bowsings and Conderton Camp. The substrate would certainly affect the shape of pit, with stable undercutting only practical on chalk and limestone, far less so in gravel. In addition to this traditional classification, the general form of pits at a site can be broadly divided into three main groups on the basis of their potential openness to the atmosphere, a feature relevant to discussion of function (TABLE 3). 'Constricted' pits have reduced apertures relative to the general diameter of the interior (Bersu's 'conical', and 'beehive-' shaped types), 'neutral' pits have apertures approximately equal to those of the interior ('cylindrical and 'barrel-' shaped types'), and 'open' pits have apertures greater than those of the interior ('bowl-shaped' pits). Published data from the above

The shape of pits (FIGS 12-14; TABLES 2, 3) -survival of data Truncation of sites by ploughing damages the upper levels of pits, and decreases their depths, often rendering analysis of original size and detailed form difficult. Where pits are entirely cylindrical, planar erosion only affects estimation of original depth, but removal of any originally overhanging upper sides of a pit can change its apparent shape from beehive or conical towards cylindrical (shapes after Bersu 1940; FIG 14b), thereby further distorting the data. Weathering and collapse of pits, if left exposed after

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experimental Iron Age grain storage sample of sites can be re-grouped on this basis as follows, although in the frequent absence of complete sets of drawn pit sections this can only be based on clearly tabulated data or selected drawn sections. These latter are provided at Danebury (Cunliffe 1984), Gussage All Saints (Wainwright 1979), Gravelly Guy (Lambrick and Allen 2004), and at Little

Woodbury (Bersu 1940, fig. 10). Other complications may arise for classification if original form is obscured by truncation of the pit, or by collapse of the upper edges, this latter converting 'neutral' to 'open' forms, especially in softer substrates such as gravel.

TABLE 2: Shape of pits at a range of Iron Age sites Bersu Selected sites: (%) of pits in type PIT (1940) DANEBURY GUSSAGE LITTLE PARKGRAVELLY FORM type ALL SAINTS WOODBURY BOWSINGS GUY cyl A 56 cyl B 23 cyl C 17 41 29 13 cyl A-C 39 conical D 0.5 10 21 beehive E 71 15 D/E 13 barrel F 46 6 other 12 40 8 40 TOTAL pits

1062

260 190 out of 477

CONDERTON CAMP 78 22

39

37

TABLE 3: Regrouping of pit shapes on the basis of openness. GROUP of pit constricted neutral open other

Selected sites (%) of pits in type DANEBURY GUSSAGE LITTLE PARKGRAVELLY CONDERTON WOODBURY BOWSINGS GUY CAMP 71 13 44 21 23 87 51 79 39 78 5 21 22 22 6

-

40

-

18

-

background of more wide-spread pit forms.

Although no consistent trend is apparent in this small sample of data, 'neutral' forms tend to predominate, with 'constricted' and 'open' forms present but in the minority. This might fit well with the notion of diversity of access to stored bulk, some pits being efficiently sealed and well-camouflaged, some as accessible and more ventilated reserves.

-quantifying overall shape The most useful general statistic on shape is the ratio of mean depth to mean diameter, further defined in the section 'Basic statistics used for analysis of pit groups'. More complex measures of shape could be used, but these serve to divide rather than unify the data, and are less robust, given partial data from variously eroded pits.

The degree to which pits are constricted in terms of the ratio between area of mouth and that of rock walls can be further quantified by calculation of the 'venting factor' (V), a measure of shape based on functionality, as discussed in the section 'Basic statistics used for analysis of pit groups' (FIGS 18-20).

The substrate into which pits are cut Pits are cut into many different substrates, with most examples from areas of harder rock such as chalk or limestone, but with gravel also well represented. Increased practicality of pit storage in well-drained areas of harder rock is to be expected. A range of lined and unlined cylindrical and beehive pits dug into these harder rocks, and into softer sand, gravel, or marl, all operated well during storage experiments, except for the clay substrate which tended to flood (Reynolds 1974).

There is a suggestion at some of the sites for what may be distinct regional practices in pit construction. For instance, stepped pits occur at The Park, highly conical pits at Danebury, timber linings and a composite silo at Conderton Camp, all finding few parallels elsewhere and standing out from the

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experimental Iron Age grain storage to cap efficiently in this way, and it is for this sector that provision of a conical cap or roofed superstructure would seem more likely on practical grounds.

Pit coverings There is almost no physical evidence surviving in the archaeological record to indicate the sealing mechanism used for pits: for instance, none was found amongst the large sample of pits at Danebury, Hants. (Cunliffe 1984; Cunliffe and Poole 1991). This general absence might suggest a disposable earthen and rubble capping, perhaps caulked or turfed over, necessarily destroyed on broaching the pit. Equally, it could suggest a removable lid, perhaps of clay-caulked, hide-covered wicker, or indeed a larger, more robust, roofed, accessible, movable superstructure, simply placed and remaining stable under its own weight, neither possibility leaving much if any physical trace. Clear evidence is unlikely to survive, especially given the widespread erosion of upper levels at many sites.

If such a pit was already under some outer superstructure, then covering its opening rather than sealing it would be sufficient, using a combination of planks, hurdling, animal skins, or straw to shield the contents, whilst maintaining adequate aeration to reduce growth of mould and decay. At Little Woodbury, Bersu suggested (1940, 60-64) that pits were capped by lids, possibly with wooden frames covered with stretched animal hide, and perhaps caulked with clay. Some degree of access was implied, noting that although there was no sign of cut steps there, ladders may have provided access to deep pits. The suggestion that storage pits 'must have been protected from the weather, either under the huts themselves, or roofed over separately, probably thatched', was made on the basis of excavation at the early Iron Age settlement at All Cannings Cross, Wilts. (Cunnington 1923, 60-73; Fowler 1983, 180-185). Five of the 75 pits excavated were thought to have provided evidence for domed roofs of fire-hardened clay reinforced with stones, but the structures illustrated are unconvincing. For instance, plate 3 shows a pit with cover, plus entrance-passage, involving an improbably perched 'lid'. The status of these features must remain questionable, given that evidence for such 'domes' are generally lacking from the archaeological record elsewhere.

At Portland (Dorset), an early excavation recorded some 20 pits with narrow mouths which were closed by single stones, one pit containing carbonised grain (Wainwright 1968). Stake holes around pits, as for instance near pits 13 and 35a at Tollard Royal (Wainwright 1968), or at Manor Farm, Guiting Power (Saville 1979) may suggest protection for the immediate area of the pit, but this does not provide further information on the method of covering, beyond its vulnerability or fragility. A seal at the top of the pit, over the straw-protected surface of the grain, could be provided by a layer of clay, topped off with turf, and perhaps then with timber or vegetation to further shield or conceal it, as may be suggested by Tacitus in Germania (chapter 16, section 4). Any sealing would work better if the top of the pit was narrow, perhaps at no more than a metre, and especially so if further constricted, as seen in certain conical pits (FIG 15a). A large open mouthed cylindrical pit, perhaps 2-3m across, of which there are many examples, would present more problems to sealing, one of the arguments used in this analysis to suggest the existence of accessible covers placed over such silos. The large seal required for this type of pit would contain considerable quantities of clay, perhaps not readily available in areas of chalk and limestone. Large seals might also tend to sag and crack under their own weight, and hence be prone to leakage. Analysis of diameters for a sample of 215 pits from Iron Age sites in southern England, with a range from 0.6 to 2.7m diameter, gives a mean of 1.43m (s.d. 0.38)(FIG 15b). This indicates that many diameters, most being greater than a metre, were large enough to have presented problems if to be capped successfully at ground level against rainfall. A significant proportion of pits, from 1.5 to 3m diameters, would have diameters extremely difficult

Placement of certain pits at Wyndyke Furlong (Muir and Roberts 1999) suggests that they may possibly have operated within huts, although the majority of pits at this Iron Age settlement appear to have lain outside. Similar interior storage is also suggested by pits which may have been located inside huts at Itford Hill (Sussex), and Fifield Bavant (Wilts.) (Reynolds 1974; Fowler 1983), and is also possible at Conderton Camp, as in hut 4 (Thomas 2005). The lifespan of pits Suggesting a value for the average lifespan of a pit is largely a matter of reasonable guesswork, tempered by observation of the condition of experimental pits after single use. Lifetime would be expected to vary quite widely since both singly and multiply used pits are known from the ethnographic record, with perhaps larger pits more eligible for reuse because of the effort invested in their construction. During longer use more wear and the need for periodic repair might be expected, this and the risk of faulty storage outweighing the labour involved in digging a replacement. Factors such as possible re-cutting and use of linings affect the lifespan of a pit. They

89

experimental Iron Age grain storage 5, p 95 and table 8, p 97). Here, the light ground-set timber uprights were close to the wall of cylindrical pits, allowing little air-gap and hence reduction in storage space, and showing no clear evidence amongst the timber holes for replacement or repair. Individual stone slats, placed between timber uprights and the rock wall are seen in pits C and D (Thomas 2005: plates 49-51/ pp. 99-100), acting to secure the base of light timber linings and perhaps providing an air gap to improve marginal ventilation of the contents. The effectiveness of such a feature would be greatly increased if this air-gap, rather than being sealed in, vented into an upper covering structure, perhaps more likely in the case of the wider and deeper pit D. Uprights could have continued up to above ground level, lashed within any pitched superstructure covering the pit, to provide a more stable overall framework. If these linings were wattle then extensive use of hazel or willow is not reflected in the char sample from the site.

relate to the actual meaning of the cumulative pit count at a site, as to whether each pit represents a single pit or a pit site, and hence they are important in developing a simple quantitative model for grain storage. Multiple use seems more likely to have been the norm for the Iron Age pits which are the subject of this analysis. Values between 5 and 10 years appear to produce the best fit with the known archaeological and likely agrarian context of sites when substituted into the simple model proposed for pit-based storage outlined below (see 'A model for grain storage'). -extension of working life by cleaning There seems to be no reason why a pit, after emptying, cleaning, and exposure to the air for the summer months could not be returned to near pristine condition for the next harvest, perhaps by slight wholesale enlargement. The crust of decomposed grain which forms over the walls of pits after over-winter storage (PLATE 7) can be easily removed manually, and the existing rock surface scraped or cut back slightly, perhaps with additional sterilisation of micro-organisms and any pests by firing.

Exceptionally, the wicker lining itself has been preserved, as under waterlogged conditions at Dragonby, Lincs (May 1996, 67, 110-111; plates 13 and 26). At Poxwell, Dorset char around the margins of a pit has been suggested as the remains of a lining (Hurst and Wacher 1986, 64-65, plate II). At Gravelly Guy there was very weak sedimentary evidence which might indicate traces of wicker in some pits (Lambrick and Allen 2004).

It is possible that rounded bases in certain pits may indicate repeated cleaning out, this feature becoming more noticeable in the archaeological record only for pits dug into a softer substrate such as gravel, as suggested at Gravelly Guy (Lambrick and Allen 2004). Here too there is some evidence for possible burning-out of pits, perhaps to enable reuse: 24 pits had thin layers of ash and char at the base, but no grain enrichment, and two pits had fire-reddened sides, with two containing significant carbonised grain (Lambrick and Allen 2004).

Use of a removable wicker, or clay lining is not without its own problems for maintenance and avoidance of cross-contamination (Reynolds 1974; Fowler 1983, 180-185). Reynolds (1974) noted the effectiveness of clay linings in experimental use but that, on emptying the pit, they tended to come away with the marginal layer of decomposing and germinated grain. Annual replacement of these mould-contaminated sleeves is to be expected.

-use of linings Lining a pit should act to improve its efficiency since decay of grain might be reduced by holding it away from damp bedrock and, if a gap exists between lining and wall, by ventilating the margins. A lining might be applied directly to the rock face, perhaps as a clay-based plaster, which could be baked by flash-firing. A wicker sleeve, which could be caulked in a similar way, or a lining of dry-stone work would provide both damp-proofing and marginal ventilation. If such linings were replaced regularly this would act to extend the lifespan of pits, the lining being disposed of rather than the pit itself.

Slat lined pits also occur occasionally, as at Manor Farm, Guiting Power (Glos.) (Saville 1979) and Condicote Camp (Thomas 2005), and would also have acted to keep the margins of stored grain out of direct contact with damp rock walls, and allow at least some aeration. Again, these linings show no sign of replacement or repair, but removal and cleaning by weathering between storage seasons would have been simple. Changes in properties of pits over time At several sites, for which adequate chronology exists, the changing pattern and nature of pit construction can be charted over time.

Evidence for linings in pits is very limited, most examples presenting unmodified rock walls. However, at Conderton Camp, stone and timber-?wattle linings were more in evidence: stone lining (8%) or stone patching (11%), timber lining (24%), and clay patching (18%) (Thomas 2005: table

At Danebury (Cunliffe 1984; Cunliffe and Poole 1991), the greatest number of pits belong to the early phase of the Iron Age, when the distribution was mainly over the centre of the interior, numbers

90

experimental Iron Age grain storage declining in later phases, with the distribution becoming more scattered (Whittle 1984; Cunliffe 1984). Mean pit volume increased steadily over time, more markedly so in the final phase (TABLE 4). Here also, beehive-shaped pits became more frequent over time, suggesting increased adoption of this form as the most effective option for storage (TABLE 5). Many other sites show a distinct

increase in pit numbers during the middle Iron Age, as opposed to the early and later Iron Age, as seen at Wyndyke Furlong (Muir and Roberts 1999). At Gravelly Guy, the mean volume of pits, the frequency of larger pits, and the total storage capacity increased into and during the Iron Age (Lambrick and Allen 2004).

TABLE 4: Danebury: changes in mean volume of pits over time. PHASE

DATES BC

1-3 550-450 4-5 450-400 6 400-300 7-8 300-100/50 TOTAL PITS

PITS mean vol. datable total vol. (m3) % (m3) 2.18 57 1163 2.43 15 345 2.79 11 279 4.35 17 691 933 2478

TABLE 5: Danebury: changes in form of pits over time (Cunliffe and Poole 1991, microfiche 24: frame E11). PHASE 1-3 4 5 6 7 8

DATES BC/AD 550-450 450 -400 400-300 300 -100/50

PIT COUNT Grand total 772 % of grand total

PIT PROFILE (%) bh cyl subrec 53 12 9 59 2 4 65 10 3 61 6 2 80 7 1 61 3

con 1 1 1 -

uncl 25 35 22 30 10 36

471

66

44

6

185

61

9

6

1

24

Key: pit profiles: bh beehive; cyl cylindrical; subrec subrectangular; con conical; uncl unclassified.

At Gussage All Saints (Wainwright 1979), pit numbers and mean volume again increased over

time (TABLE 6), but there are no published data available on any detectable changes in pit form.

TABLE 6: Gussage All Saints: changes in mean volume of pits over time. PHASE DATES BC 1 c 500 BC 2 c 300 BC 3 to 150 AD undated TOTAL

PITS mean vol. datable (m3) number % 1.79 128 27 3.00 69 14 2.77 184 39 96 20 477

At Gravelly Guy (Lambrick and Allen 2004), the number of pits, their mean volume, and hence the total storage capacity at the site, increased during the middle Iron Age (TABLE 7). There is no very clear

total vol. (m3) 229 207 497 933

trend in the form of pits over time, beyond a slight increase in those with undercut sides between the early and middle Iron Age (TABLE 8).

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experimental Iron Age grain storage TABLE 7: Gravelly Guy: changes in mean volume of pits over time. PHASE

PITS number mean

total

volume (m3) lba 2 eia 229 [lba/eia]

0.6 1.1

mia 402 ia 265 [mia/lia]

1.0 0.5

storage (m3)

number >1m3 (%) 39

220 45 455

Key: lba later Bronze Age; eia early Iron Age; mia middle Iron Age; lia later Iron Age.

TABLE 8: Gravelly Guy: changes in form of pits over time. DATE lba eia mia ia

PIT PROFILE U C 1 54 ( 6) 100 111 (12) 163 22 ( 2) 90

(% of grand total [*] B S 1 (11) 46 (5) 7 (1) (18) 66 (7) 12 (1) (10) 83 (9) 27 (3)

given in brackets) M total 2 22 (2) 229 50 (6) 402 43 (5) 265

total

187 (20) 354 (39) 196 (22) 46 (5) 115 (13) 898*

Key: for date: as TABLE 7; pit profiles: U undercut; C cylindrical; B bowl-shaped; S saucer-shaped; M miscellaneous.

Application of these statistics to pit groups from the location of the experimentation at The Park-Bowsings and from other Iron Age sites in southern Britain indicates that their general form tends to favour shallowness, openness, and improved ventilation, rather than optimising containment within a closed system.

BASIC STATISTICS USED FOR ANALYSIS OF PIT GROUPS Conclusions on the general conditions for successful operation of grain storage pits, as suggested by specific experimental results, must be viewed against and integrated with whatever structural data can be obtained from the assemblage of pits at the immediate site, and from other comparable external groups. A range of descriptive statistics of general currency is therefore essential as a basis for such comparison.

Publication of pit groups should include a complete set of plans and sections from which primary data can be obtained. General statistics should include means for depth, diameter, depth:diameter D, volume, venting factor V, and exposure E, all with stated standard deviations. A linear regression line for depth on diameter (FIGS 16-17) provides a further assessment of pit openness at a site, far better than the single value of mean depth:diameter often given in isolation, which represents only one point on the regression line. Sites could produce similar values for mean depth:diameter, but still have different regression lines, obscuring more general differences between their pit groups, as seen where regressions of different slope intersect at or near a common mean (FIG 17).

The properties of pit-groups are described in this analysis with reference to four basic interrelated statistics: volume, ratio of depth to diameter D, venting factor V, and exposure ratio E, derivation and use of which are outlined below. Pits can also be classified according to shape, in this analysis descriptively without quantifying further. Such measures can be used to discuss variation between storage conditions at sites, or to highlight general use of common methods to confront universal practical problems. Use of data on pit depth in any of these calculations can be done as it survives, or as a re-estimated original, if the degree of truncation can be gauged.

A summary of basic statistics given for a selection of published sites is as follows (TABLE 9):

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experimental Iron Age grain storage TABLE 9: General statistics for published pit groups (ranking data by decreasing mean depth). # MEANS and std. devs. substrate pits depth diam. depth vol. excav. (m) (m) :diam. (m3) data derived from re-analysis of detailed metrics given in publications Tollard Royal C 31 1.08 0.46 1.17 0.40 0.93 0.25 1.99 2.07 Birdlip L 17 1.01 0.28 1.12 0.19 0.9 0.18 1.09 0.62 Little Woodbury C 54 1.21 0.54 1.36 0.31 0.86 0.28 2.11 1.74 Conderton Camp ) L 38 0.88 0.34 1.42 0.47 0.65 0.25 1.63 1.43 Park-Bowsings L 58 0.94 0.35 1.44 0.30 0.65 0.17 1.77 1.39 Sherbourne House g 68 0.86 0.29 1.59 0.41 0.54 0.16 1.99 1.48 site

partial data cited in publications Gussage All Saints C 381 1.26 0.46 1.45 0.33 0.78 0.53 Gravelly Guy g 898 0.57 1.17 [0.49] Beckford g 0.97 1.64 [0.59] Kemerton g 39 0.6 1.4 [0.43] Danebury C 1282 0.95 Key: substrate: C chalk; L limestone; g gravel. [] best estimate

venting factor V

exposure E

0.17 0.22 0.24 0.30 0.29 0.33

0.23 0.22 0.26 0.24 0.26 0.27

0.04 0.04 0.07 0.09 0.07 0.07

0.22 0.04 0.07 0.07 0.06 0.07

2.45 0.87 2.12

ref. 1 2 3 4 5 6 7 8 9 10 11

for the statistic.

ref(erences): 1: Wainwright 1968; 2: Parry 1998; 3: Bersu 1940; 4: Thomas 2005; 5: Marshall 2007; 6: Bateman et al. 2003; 7: Wainwright 1979; 8: Lambrick and Allen 2004; 9: Dinn and Evans 1990; 10: Dinn and Evans 1990 quoting Wills (forthcoming). 11: Cunliffe and Poole 1991.

Volume (FIGS 10-14) In this analysis volume is calculated for each pit from its mean diameter and depth, assuming a basically cylindrical shape if this is a close approximation, or by more specific calculation if it is not. The range of volumes observed for the group is expressed as a histogram of frequencies, to display the distribution of different capacities and establish the presence of any sub-divisions within the group.

-the regression line relating depth and diameter (FIG 17) .. its inclination The slope of the regression could provide some indication of the basic strategy for Iron Age pit construction, whether for instance to produce pits which were deeper and more constricted or shallower and more open. Given equal scaling of the x- (diameter) and y- (depth) axes, if the slope of the regression line is about 1 (tan 45o) then depth tends to equal diameter, if less than 1 then the trend is towards shallower pits, and if greater than 1 then the preference is for deeper pits.

Shape Shape may provide some insight into function, as noted for the conical type with its highly restricted aperture, and the large open silo type. Shape is noted qualitatively for each pit according to the system of Bersu (1940) (FIG 14b), and tabulated for the group as the percentage of each type present. Shape can be simplified on the basis of mouth- to body-aperture, into 'constricted', 'neutral', or 'open' types (TABLE 3). For the majority of pits, which are basically near-cylindrical, the following simple statistics are presented here as useful for comparisons between groups:

When considering such graphs it is important to note that, whilst the drawn regression lines tend towards a theoretical zero for diameter or depth, in practice there are minimum values for these dimensions, below which the hole in question is too small to be regarded as a candidate pit. A lower limit for plotting regression lines has therefore been set at 50cm, for both depth and diameter, these giving a capacity of about 0.1 m3. On practical grounds, capacities for actual storage pits are likely to be well above this value.

-the relationship between depth and diameter ..the ratio D (FIGS 16-19) The ratio D for an individual pit is defined as mean depth divided by mean diameter. For groups of pits, depth is also plotted against diameter for each pit, and the resulting scatter of data used to determine a linear regression line, this latter summarising the relationship between these two dimensions. This linear regression line is of the form y = mx + c, where y is depth, x is diameter, m is the slope of the line (tangent of its angle with the x-axis), and c is the value of its intercept with the y-axis.

..differences of interval between regression lines (FIGS 16, 17)

parallel

Erosion of pits, by modern ploughing for instance, decreases their original depth whilst, for a basically cylindrical pit, leaving the diameter relatively unchanged. Given adoption of fairly standard procedures by Iron Age farmers for successful construction and operation of generally cylindrical pits on a particular type of substrate, the slope of the regression line of depth against diameter should remain similar for both uneroded and eroded sites, but at the latter the line will be in parallel and further

The disposition of such regression lines could provide useful comparative information between pit-groups:

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experimental Iron Age grain storage reflected by differences in the slope of regression lines between sites. Sites with a preference for deeper, more constricted pits should produce different regression lines than those at which shallower, more open pits were the norm. For instance, most pit groups on drier upland limestone sites produce regression lines with slopes around 1, that is about 45o, as at Little Woodbury, Tollard Royal, and The Park-Bowsings. However, several examples on valley gravel sites produce less steep regression lines, with slopes less than 1, indicating a preference for shallower pits. This may reflect the greater difficulty of digging deeper pits with stable sides in the softer gravel, as well as the need to keep pits shallower, with their contents well above the water-table, and in the case of unsealed pits, able to vent more effectively. Two such cases are shown, at Sherborne House, on gravel, and at Conderton Camp, on lower limestone slopes, these latter perhaps less well drained than those at higher altitude.

down the y- (depth) axis, provided that all pits have been fairly equally eroded. The interval of this depression should give some estimate of the extent of truncation, and could allow some attempt to re-establish the original regression line for eroded pit groups (FIG 16). On individual sites some indication of the extent to which pits are likely to have been truncated can also be given by the surviving depth of features such as post-holes. The original depth of certain post-holes, as determined by practical, structural considerations, can be estimated with some accuracy, providing a measure which can be added to surviving pit depth to give an estimate of the original. For instance, at Tollard Royal, Wilts. (Wainwright 1968), post-holes for fairly substantial 'granary structures' were about 25 to 50cm deep, indicating that about 35cm of the upper part may have been removed, this value then being used for any restoration of pit depth undertaken. This of course assumes that erosion has been fairly constant over a site, which may not be the case. In other cases the presence of nearby intact surfaces, such as those of hut interiors, can indicate that erosion of pits has been minimal, as was concluded at The Park (Marshall 2007).

The trends evident from fuller regression analysis of depths and diameters for pits on different substrates are also seen in summary form by comparing mean values of the ratio depth:diameter between sites, often the only statistic published. This analysis also indicates that pits on gravel tend to be shallower and more open than those on harder rock (TABLE 10).

..differences of slope between pairs of regression lines (FIG 17) Different practices for pit construction should be

TABLE 10: Differences in mean depth:diameter for samples of pits on different bedrock, with correction of depths to allow for later truncation (ranking data by decreasing mean depth). [Dimensions in eroded eroded Site mean mean depth depth: diam. calculation >> a b substrate: limestone-chalk Tollard Royal 1.08 0.93 Birdlip 1.01 0.90 Little Woodbury 1.21 0.86 Gussage 1.26 0.78 Park-Bowsings 0.94 0.65 Conderton Camp 0.88 0.65 Manor Farm 0.54 0.36 substrate: gravel Gravelly Guy 0.57 Sherbourne 0.86

0.49 0.54

metres] original depth eroded by c

correction for actual depth d=(a+c)/a

corrected mean depth: diam. b*d

0.35 0.20 0.25 0.30 0.10 0.10 0.40

1.32 1.20 1.21 1.24 1.11 1.11 1.74

1.23 1.08 1.04 0.97 0.72 0.72 0.63

0.25 0.20

1.44 1.23

0.70 0.67

Note: Danebury is not included: precise data not available in Cunliffe 1984 or Cunliffe and Poole 1991. Key: in the row indicating 'method of calculation', '/' indicates division and '*' multiplication.

94

experimental Iron Age grain storage E and V vary according to depth and diameter as shown in FIG 18a. The sample of excavated pits from The Park-Bowsings is shown superimposed on graphs of V and E in FIG 18. The distribution indicates that although they occupy a similar band of V, between 0.2 and 0.3, their values of E differ markedly, over a three-fold range, from 0.15 to 0.45. Ventilation properties, actual for unsealed and potential for sealed pits, are therefore similar throughout the size range, but exposure of unit volume contents to damp rock wall is not. Similar conclusions can be drawn by plotting pit-groups from other sites, and differences noted between samples. These ranges of V and E in FIG 18 may reflect intentional design: provision of pits suited to different types of grain storage, from smaller quantities of sealed seed-corn to far larger volumes of accessible food-grain. In the case of the latter the priorities might be to provide a higher volume of bulk storage, held at increased ventilation and decreased exposure, aspects in some degree of opposition at different selections of depth and diameter.

Measures of susceptibility of stored grain to hydration by ground-moisture Two basic statistics attempt to quantify operational properties of pits in relation to throughput of moisture, the ratios V and E, as outlined below. These values indicate the relative exposure of pit-contents to hydration by penetration of ground-moisture (E), and assess the potential ability of pits to ventilate this trapped moisture (V). -the relative exposure of the contents of a pit to the damp rock forming its sides and base: the ratio E (FIG 18b). As the volume of a cylindrical pit increases, the area of the stored grain exposed to its damp rock walls increases in absolute terms but decreases per unit volume stored. For any given volume, the relative exposure of stored contents to damp rock also changes according to the shape of the pit, for instance a deeper, narrower pit involving more exposure to damp rock than a shallower, wider one. Simple geometry of a cylinder shows that the ratio E (volume stored per unit surface area of rock-face) is given by

Typical silos, such as those plotted in FIG 18, there with depths of about 1.5m and diameters of about 2m, achieve a good balance of V, E, and volume, with V 0.2-0.3, E around 0.4, and volumes about 5.5m3. An increase in diameter rather than depth would be the best strategy for further improvement, and this is seen in even larger silos with diameters around 3m found elsewhere, as at Middle Ground, Temple Guiting (Marshall 1999). Additional features such as splaying of pit sides (The Bowsings), and marginal internal slatting (Manor Farm; Condicote Camp), both acting further to improve ventilation, might reflect this need for improved efficiency in large, critical storage units for food grain. This effectiveness would be needed since the storage period for at least some food-grain would be from harvest to harvest, a year or more, although contents would be regularly depleted by use and perhaps other stocks added. This period is twice as long as that likely for seed-corn, perhaps stored in the smaller non silo-pits from harvest to a spring planting, over about 5 or 6 months.

E = V/A = depth/((4*depth/diameter)+1) where 'V' is pit volume, and 'A' is the area of damp rock forming the sides and base of a pit of given depth and diameter. As E increases the exposure of contents to damp rock decreases, improving bulk storage. Minimising loss of spoilt grain at the edges of a pit and decreasing penetration of damp into the main bulk would therefore be best achieved by use of larger pits of shallower depth. These proportions would also increase the ability of the pit to ventilate, if unsealed but covered (see: discussion of venting factor, below). -potential openness of pits to ventilation, venting factor V (FIGS, 17a 18, 19). The venting factor V is the ratio between the area of the aperture of a pit, which remains at least potentially open to the atmosphere, and the combined areas of its sides and base, which are exposed to damp rock. V gives a measure of potential to vent damp air, if the pit is left unsealed but protected from the elements. V is obtained by simple calculation from the properties of a cylinder, as follows:

At the other end of the size range are these non silo-pits, the examples shown in FIG 18 typically with depths of about 70cm and diameters of about 1m, with volumes 0.5-1m3. Although they have a potential for venting, if left open, comparable to that of silos, they have far lower values of E, meaning that their contents have at least double the exposure to damp rock walls per unit volume than silos. If a feature of design rather than an unfortunate consequence this might suggest that a degree of hydration of contents was acceptable, perhaps desirable for ease of early growth if grain was to be scattered as seed.

V = 1/(1+(4(depth/diameter))) As V increases so does the ability of the pit to ventilate contents if left unsealed.

95

experimental Iron Age grain storage The general structure of a basic model is shown in FIG 26, which summarises assumptions made and restrictions imposed by absence of relevant archaeological data. Flow of grain through the model is as follows. Arable land under current cereal production produced a certain level of grain which was harvested during late summer or early autumn. Part of this could have been retained without storage, either as food, as seed for a possible autumn sowing, or for immediate trading out of the system. This fraction would have no impact on the need for longer-term storage facilities. The remaining and presumably larger fraction would have been stored in pits or above-ground granaries, divided between seed-corn, returned later to the cycle of cultivation, and food-grain consumed by site population or impacting on trade.

Pits at both ends of the range were used for experimental purposes, the smaller type used sealed, and larger left unsealed. A MODEL FOR GRAIN STORAGE (FIG 26) Assuming that grain storage was the main function of the pits in question, as is suggested by most current evidence, it is possible to propose a simple ergonomic model for their operation within the general format of grain cultivation and consumption at Iron Age settlements. Available archaeological and agronomic data can be used to calibrate such a model and test its plausibility. Such a model provides an essential context for further supporting the case for primary use of pits for grain storage, for discussion of detailed usage, and for interpretation of experimental results.

Certain variables are set to zero in the model, either because data are lacking, or to maintain the simplest case. For instance, the fraction traded into or out of the system at various stages can not be included, except as unsupported guess-work. A value for the fraction utilised immediately before storage is similarly inaccessible. Most significantly the contribution of above-ground granaries to the system can not be included without far better data on clearly identified structures than is currently available. At a very basic site such as The Park-Bowsings the apparent absence of candidate post structures may indicate that this factor may actually be set close to zero. This is certainly not the case at such sites as Danebury where such features, of uncertain interpretation as granaries, are very well represented.

The analysis and experimentation in this study is centred on interpretation of the simplest case, grain storage at a small farmsteading unit at the base of the Iron Age economy, on a limestone bedrock. Other such site and those of greater complexity are included wherever possible, from surrounding areas comparable in terms of substrate and regional culture, and where excavation has provided a sufficient, clearly documented sample of pits. This is supplemented by parallel data from sites on the chalk-lands of Wessex which have produced large samples of pits. A general introduction to agriculture amongst the sites in question is given in Reynolds 1976 and 1980. Reynolds (1988, 26) is pessimistic about the development of viable models for grain storage, for reasons which the author (AJM) does not fully understand. Reynolds rejects modelling on unspecified experimental grounds, and states that since the pit is a passive container its lifespan can not be calculated because the factors which can cause failure of storage, micro-organisms, are all on the grain itself. The author (AJM) would argue that the pit is anything but passive, the efficiency of its walls, seal, and weatherproof cover, being major factors determining success or failure. Surely sensible upper and lower limits for mean lifespans of pits can be proposed as the basis for preliminary modelling.

In this simplified model the grain cycle has been considered in isolation from other factors which would be essential in sustaining a population, such as cultivation of non-cereal crops and pastoral activities, all factors highly important in a fuller economic and ergonomic analysis. In view of the sheer quantity and range of unknowns at prehistoric settlement sites such simplification is required to produce any sort of working model relevant to pit storage at all. Approximation of the model to more complex economic reality is somewhat justified by the latitude already introduced for certain elements, by working between broad realistic limits for key values in the grain storage system rather than a particular figure. For instance, bracketing the assumed lifetime of pits to between 5 and 10 years, as done in the model, affects all subsequent calculations of arable extent and site population in a way which may render possible corrections from other aspects of the non-grain economy fairly minor. Work is currently being undertaken by the author (AJM) to elaborate the model and refine its operation by application of hard data.

Some of the problems in using data on the number and size of pits at a site to help define aspects of the arable economy and population size were further noted by Reynolds (1999, 159). It is nevertheless possible to propose a general working model, the key variables for which can be more closely defined by experiment or from the archaeological record, with necessary simplifications and uncertainties clearly stated and presented as open to alternative recalculation. Such an approach has been adopted in this report.

96

experimental Iron Age grain storage upper and lower limits in mind at each stage, to produce a 'bracketed' result, for generalised discussion.

The point of contact between the experimentation presented in this paper and the model lies in data provided by the former on performance of pits for grain storage. It confirms the potential of larger types as covered granaries, helps to indicate an improved level of storage success without sealing, suggests division of the crop between seed-corn and food-grain, and quantifies levels of wastage.

The term 'constant' is used here, not in the sense of its value being fixed, but to indicate that it can be more readily given a realistic value from external sources, such as experiment or the archaeological record. For instance, 'yield' and 'wastage' would depend on immediate conditions, but can be reasonably approximated. 'Variables', on the other hand, are less easily given a mean or bracketed value, and contain the elements for which the model is trying to derive limits.

Definition of variables and constants The values used for all constants must be regarded as an approximate best-estimate, based wherever possible on other experimental determination. The sequence of calculations has been carried out with

-variables (given in upper-case letters) can be defined as follows: I P

the active lifespan of a pit; number of pits in contemporary use during each interval I; S total stored grain from each harvest; A area under cereal cultivation, as judged from the total volume of stored grain; X population of adults supported, as judged from the total volume of stored grain; To grain traded out of the system after storage Ti grain traded into the system before or after storage; G number of above-ground granaries in contemporary use during each interval I.

QUANTITY years number volume area number fraction fraction number

-constants (given in lower-case letters) are as follows: ..site-specific constants, determined from the archaeological record: t

proportion of the site producing data on pits, and assumed to be representative;

QUANTITY fraction

total number of accumulated pits: nt recorded at the site by excavation; n projected for the site, based on best data;

number

d

the entire pit-using phase at the site;

years

v

mean pit volume.

volume

..'universal' constants:

value

conversion of volume to weight for grain: [1] modern tonnes/m3 or as m3/tonne [2] ancient tonnes/m3 or as m3/tonnes

used

source

0.601 1.66 0.55 1.82

e,o

Note: grain is discussed in terms of volume rather than weight where possible.

g

mean grain-yield per hectare cultivated; tonnes/ha or after conversion [2] m3/ha

97

1.68 3.05

R

experimental Iron Age grain storage

c

grain consumption per adult per year; 0.5 m3 kr seed-corn: proportion retained for sowing fraction 0.20 : proportion actually sown ks fraction 0.05 w proportion of grain wasted in storage fraction 0.05 r sowing rate kg/ha 63 or after conversion [2] m3/ha 0.115

R p,R

e R

Key: source of values: R (Reynolds 1979); p (personal estimate); e (personal experimental data); o (other data files). Justification for values adopted as universal constants is outlined in more detail as follows:

Various data from Butser Ancient Farm provide an estimate of cereal yields:

...constant 'n' (the total number of pits accumulated at a site): Here, the best estimate for the total number of pits (n) which accumulated at a site may have to be obtained from the number of pits actually recorded in a sample excavated area of the site (nt), divided by the fraction of the site explored (t), assuming this fraction to be representative of the entire site in terms of pit distribution.

Data set 1: Experimental cultivation over 8 consecutive years at a sowing rate of 63kg/hectare on unmanured ground gave the following yields for emmer and spelt wheats (Reynolds 1985, table 1/ p.399): spelt: mean 1.76 (range 0.7-2.4) tonnes/hectare; yield of seed: 1:28.6 (range 1:14-1:40); emmer: mean 1.85 (range 0.7-3.7) tonnes/hectare; yield of seed: 1:30 (range 1:7-1:59); Application of manure at 20 tonnes/hectare for 3 consecutive years increased the yield of bulk grain. The mean over 2 years for emmer was 3.92 tonnes/hectare, with yield of seed 1:62.5 (Reynolds 1985, table 3/p.400). Data sets 2 and 3: Alternative mean yields for emmer and spelt over a 14-year period, mainly on unmanured land, are comparable to those cited above: emmer 1.65, and spelt 1.49 tonnes/hectare (Reynolds 1990, table 5/p.70). Again the dominant effect on yield was weather, with manuring also a factor. Further mean yields are available for emmer as 1.8 (range 0.4-3.7), and spelt as 1.54 (range 0.7-2.3) tonnes/hectare for Butser Ancient Farm field 2, for 5 non-consecutive years (Reynolds 1980: table 1/p. 13), again with vagaries attributed to weather.

A decision has also to be made whether to include areas outside the enclosure, where pits often occur in considerable quantity but uncertain association. Data from extensive magnetic mapping of sites is very useful in relation to estimates of total pit numbers, but only if available in sufficient resolution to enable individual pits to be distinguished (Marshall 1999). ...the constant converting volume of grain to weight: Conversion of pit volume to notional weight of modern stored grain is based on UK/US agricultural data from cereals in the form of threshed grains at about 14% moisture content, and is expressed as tonnes/m3: wheat 0.773; barley 0.618; oats 0.412. This would give a mean working value of 0.601 Personal tonnes/m3 for the three cereals. experimental determination of modern wheat and barley by the author (AJM) gives a value of 0.682 tonnes/m3 (TABLE 24). Iron age cereals were less dense and so this figure would be reduced somewhat, perhaps around 0.5 tonnes/m3.

Data set 4: A further quote suggests that a minimum of 3 to 4 Celtic fields, assuming a mean area for each of about 0.13 hectares, were required to produce 1 tonne of grain (Reynolds 1979, 71-82). Based on 3.5 field-areas as a mean, this gives a yield of 2.2 tonnes per hectare. Data set 5: Other trials have shown that spelt wheat yields 1.5 tonnes/hectare when autumn sown and manured, but 3 tonnes per hectare if spring sown and manured. One barley trial yielded 1 tonne per

...constant 'g': grain yield from arable fields

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experimental Iron Age grain storage provides such practical latitude.

hectare (Reynolds 1987-1989; quoted in Lambrick and Allen 2004).

The season of sowing determines the amount of pit storage required for seed-grain. Autumn sowing would require no longer-term storage, with pits or other facilities only needed being for spring-sown crops. The number of pits at a site may therefore give an underestimate for the area of arable in use.

The final mean yield taking all these data into account is 1.68 tonnes/hectare, or 2.00 tonnes/hectare if the single manured yield is included. The former value is adopted in the model. Assuming that 0.55 tonnes of cereal occupies 1m3, as calculated immediately above, then 1 hectare of ancient cereal cultivation would require about 3.05m3 of pit-storage. Of course greater uncertainty can be introduced into the model by adopting not a single value but a range for yield, and this might help compensate for annual variation caused by weather and condition of land. In relation to the latter, lower yield caused by decreasing fertility of cultivated areas is a feature of many discussions of prehistoric land-use, a question addressed experimentally at Butser Ancient Farm. Here, repeat cultivation of of emmer and spelt wheat on unmanured experimental plots over an 8 year period saw no evidence for soil exhaustion, as measured by stable levels of organics and key inorganic nutrients and by the lack of any significant decrease in cereal yields, variability being primarily a function of weather (Reynolds 1980: table 2/p.13) and 1985, table 2/p. 400).

Reynolds (1974a, 1980) discusses spring and autumn/winter plantings, suggesting that both may have been used to help insure against weather-related failure, noting that certain cereals such as emmer wheat performed well in both plantings but that spelt wheat tended to do better with over-wintering. The amount of seed-grain required depends on its productivity and on sowing density. Whittle (1984), quoting Reynolds (1979), cites experimental data from Butser Ancient Farm for winter-grown emmer, indicating that productivity of seed varied from 7 to 59 fold, with mean of about 33-fold, as measured in trials over eight consecutive years, with no nutrients added. On the basis of the mean value about 0.03 of the harvest would be required to produce the next. In the model this is raised, and 0.05 of the harvest is

In contrast to the above data the value for grain yield adopted in discussion of the economy at Gravelly Guy (Oxon.) was lower, at 0.8 tonnes/hectare (Lambrick and Allen 2004).

taken to be the sown fraction (ks). The amount retained for sowing is likely to have been considerably higher than this since miscalculation would have had serious consequences for Iron Age farmers. The retained fraction (kr), which includes that sown, and which required storage space, is therefore estimated as 0.2 of the crop, four times that sown, to provide a safer margin. After all, seed-grain not used for sowing could still be otherwise consumed.

Other relevant data on yields are given in Mercer 1981, and more general issues regarding cereal crop production are discussed in Araus et al. 2003. ...constant 'c': grain consumption Whittle (1984), citing Bowen and Wood (1967), quotes a value for annual per capita consumption of 12-14 bushels (1 bushel being 8 gallons, equivalent to 0.03637m3), or 0.47m3 in total if adopting the mean value of 13 bushels. Jeffries (1979) suggests that the levels of consumption used in discussion by Bersu (1940), 4.5 bushels per head per year, which were based on those current in 1938, should be increased by a factor of 2-3 for application to the Iron Age. These combined sources suggest a value for adult consumption (c) of about 0.5m3 per year and, since this seems reasonable on nutritional grounds, it has been adopted here.

...constant 'r: sowing rate Modern cereal sowing rates are cited as averaging 130kg/hectare, in drills 10cm apart, and for early 19th century Sussex as 3 bushels/acre or 162kg/hectare (assuming conversion rates outlined above), with drills spaced at 20cm or wider for manual weeding access (Reynolds 1980, 11). A sowing rate of 63kg/hectare on unmanured ground at Butser Ancient Farm, the value adopted in this analysis, gave the yields for emmer and spelt wheats noted in Reynolds 1985, table 1/ p.399; Reynolds 1987-1989). This latter value is noted by Lambrick as probably excessive (Lambrick and Allen 2004).

...constant 'k': proportion of grain harvest retained as food-grain A fraction of the harvest would be saved for sowing at the start of the next growing season. Any reserve for seed-grain is likely to exceed that needed for a first sowing, perhaps doubled to cope with up to a full re-sowing, as might be required to cover failure of the first planting, for instance from disease or frosting. The proportion of grain retained as seed in the model

...constant 'w': proportion of grain wasted during storage This has been measured experimentally in this series of experiments as 3-5%, and the upper value is used here. Only in-pit wastage has been considered in the model. Naturally, there are other potential sources of wastage for grain during processing and storage, the effect on the model varying according to

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experimental Iron Age grain storage precise location in the cycle. For instance, levels of seed loss immediately after sowing would have a marked effect on yield. Experiment at Butser Ancient Farm has shown that grain simply broadcast experiences high levels of consumption by birds, with losses of 98% being recorded. Such loss reduces to 70% if semi burial of grain by bush-dragging follows, and to 65% if tilth is timber-dragged, both levels still deemed unacceptable. However, losses are dramatically reduced if cereal is drilled in rows produced by a narrow ard, such spacing also acting to aid growth and weeding of the crop (Reynolds 1980, 11).

Development of a working model for grain storage Using the parameters defined above it is possible to describe a simple model, as a first approximation to reality, in which a batch of P pits of mean volume v provide the only means for grain storage, annually for an interval of I years before replacement with another batch of P pits, this being repeated over a total duration of d years, during which time n pits accumulate in the archaeological record. Stored grain S is harvested from an area A, to be consumed by X adults, with wastage w, and retention for seed corn k, this latter used to replant the same area A for the next cycle. The initial assumption made is that all grain was stored in pits, a storage capacity which can be directly measured, and the conclusions obtained from this capable of expansion to include the possibility of other above-ground storage. The latter is difficult to quantify since any basal structures only survive at best as post-holes of uncertain interpretation, as is the case for the 4-, 6and other post settings found on Iron Age sites.

...variables 'To' and 'Ti': proportion of seed traded out from the harvest at a site or into its general stocks from extenal sources In addition to the seed-reserve and stocks of food-grain utilised directly at a site, a further fraction of the grain harvest might be traded into or out of the system. Additions (Ti) or deductions (To) could be made to grain stocks at various points before or after the harvest, and would affect calculations in the model in a complex manner, altering the relationship between quantity of associated arable, numbers of pits required, and the level of population supported.

For the purposes of this simple general model the assumption also made is that pits were in fairly constant and regular use throughout the life of a community. In the case of Danebury, about 4500 pits spread over about 450 years of occupation give an average of about 10 pits constructed per year, although the actual pattern of pit use over time is more complex (Cunliffe and Poole 1991: figs. 4.98, 4.99/pp. 144-145).

Levels of grain traded as this 'mobile fraction' are difficult to estimate other than by guesswork. They are likely to be far less for small, self-contained farmsteads practising a subsistence economy, such as The Park-Bowsings, than for large hillforts such as Danebury (Hants.), which may have acted in part as repositories and redistribution centres for surrounding territories.

The following linked series of equations describe this model:

In view of the uncertainties involved, values of T have been set here to zero, thereby isolating grain cycles at each site from each other, obviously unrealistic in practice. Its value can, of course be varied within equation 4, say between arbitrary limits of -0.2 and +0.2, giving at least some expression to the effects of this mobile fraction on site population.

equation 1: The number (n) of pits accumulating at a site equals the number of pits per batch in contemporary use (P), multiplied by the number of mean batch lifetimes (I) contained in the duration of pit use at the site (d): n = Pd/I, or P = nI/d equation 2: The total volume of stored grain (S) for each harvest equals the number of pits per batch (P), multiplied by the mean volume of a pit (v): S = Pv

...variable 'G': number of above-ground granaries in contemporary use at a site Although many sites have produced smaller rectilinear post structures, their role as granaries remains unknown. The contribution of in-hut storage, and perhaps the existence of dedicated granary huts, introduce further unknowns. Even given clear identification of such granaries, calculation of capacity based on ground-plan alone would remain contentious. In view of these uncertainties the value of G in this basic model has been set to zero, but could be introduced into the set of equations given below, and varied within limits based on appraisal of the evidence for above-ground storage at a site.

equation 3: The total area of arable under grain cultivation (A) equals the volume of the harvest stored in pits (S) divided by the volume of the grain yield per unit area of arable: A = S/g equation 4: The number of adults (X), with individual grain consumption (c), which can be supported by the

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experimental Iron Age grain storage fraction of the pit-stored grain-harvest (S) retained as food, after removal of a proportion for seed-corn (kr), wastage during storage (w), and allowance for a mobile, traded fraction (T, which can be positive or negative according to whether traded in or out), is given as follows:

equation 5: The fraction of the harvest used for seed (ks) multiplied by the volume of stored grain (S) should approximately equal the area of active cereal arable (A) multiplied by the sowing rate (r).

X = S(1-kr-w+T)/c

ks S = Ar, or S/A = r/ ks

This preliminary model assumes a single mean lifespan for all pits, irrespective of size, history of reuse, or recutting, with the limiting values chosen as 5-10 years, based on practicality, reasonable guess-work, plus observation of the state of experimental pits at the end of the storage season. It is of course possible to refine the basic model by allocating a range of lifespans to different types and sizes of pit. Attempts to do this, with no clear data to provide calibration, have certainly increased complexity, but with very little improvement in information content. The current simple model, with minimal assumptions, does however appear to give realistic results, useful in the interpretation of archaeological and experimental data, and as a basis for discussion and improvement.

The constants r and ks adopted in the model would give the ratio of S/A as 2.3 which, if it matches the ratio obtained from equations 2 and 3 suggests that the model is in approximate balance. Testing the model at key sites It is possible to test the overall balance between these equations using data (values of n, d, and v) from contrasting sites: the large hillfort at Danebury, and far smaller enclosures at Little Woodbury, Gussage All Saints, Gravelly Guy, and The Park-Bowsings. All of these are sites where the population of pits is known with some certainty, the latter being the site of the current experimentation (TABLE 11).

TABLE 11: Data on pit-groups at selected sites used in the model of grain storage. CONSTANT

Danebury

interior (ha) 5.3 t 0.23 nt 1100 n [4783]

ParkGussage Bowsings 1.3 1 1 1 477 110 477

Little Woodbury 1.2 0.47 190 404

Gravelly Guy 3 1 915 915

Conderton Camp 2.0 0.05 max 46 150

Manor Farm 0.25 0.25 52 208

d v s.d. for v

500 1.8 1.4

500 2.1 1.7

500 0.9 -

200 1.63 1.43

500 1.70 1.34

500 2.7 -

600 2.4 -

Note: internal areas and dates of occupation have been obtained as follows for the sites named: Danebury (Cunliffe and Poole 1991, fig. 4.4); Park-Bowsings (Marshall 2007); Gussage (Wainwright 1968; Wainwright and Switsur 1976); Little Woodbury (Bersu 1940); Gravelly Guy (Lambrick and Allen 2004); Conderton Camp (Thomas 2005). At Danebury, Gussage All Saints, Gravelly Guy, and Little Woodbury the pit count is based on excavation, at The Park-Bowsings and Conderton Camp from excavation supplemented by data from magnetic mapping over unexcavated areas. A recount of pit-like magnetic anomalies at Danes Camp (Thomas 2005, fig. 4) suggests that the maximum estimate given in the report might be revised upwards from 150 to around 250 (actual recount: 267). The model would then indicate higher arable productivity, cultivated area, and population. Key: t n

proportion of site excavated; nt number of pits found in the area investigated; total number of pits estimated for the site (= nt/t); d duration of occupation (years); mean volume of pits (m3);

v s.d: standard deviation;

'-':

data not available. Estimated values of pit numbers are shown thus: [..].

A way into the model is provided by assuming limiting values for the average lifespan of a pit (I). There is little to indicate an actual value, beyond realistic

guesswork. On this basis, a value of 10 years has been suggested at Danebury for pits, and for post-built granary-type structures, the estimate

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experimental Iron Age grain storage previously suggested by Bersu (1940). This value seems high, and perhaps 5-10 years would be a

safer estimate for the mean (TABLE 12).

TABLE 12: Data generated by the model, with values of pit lifespan 'I' set at 5 and 10 years. pits total grainadults AS CALCULATED Site in use grain arable supported USING THESE area /year harvest in use CONSTANTS (ha) A (ha) X n d v SITE P S (m3) major hillforts Danebury 48-96 130-260 42.6-85.3 195-390 4783 500 2.7 5.3 small enclosures Gussage All Saints 4-8 10-20 3.3-6.6 15-30 477 600 2.4 1 Little Woodbury 4-8 8-16 2.6-5.2 12-24 404 500 2.1 1.2 Gravelly Guy 9-18 8-16 2.6-5.2 12-24 915 500 0.9 3 Conderton Camp 4-8 7-13 2.3-4.6 11-22 150 200 1.6 2 Manor Farm 2-4 3.5-7 1.2-2.3 5-10 208 500 [1.7] 0.25 Park-Bowsings 1-2 2-4 0.7-1.3 3-6 110 500 1.8 1.3 Note: sites are ranked according to decreasing projections for total grain harvest. Values bracketed thus [..] have been obtained after compensation for eroded depth of pit.

Allowing values for the lifetime of pits (I) of between 5 and 10 years, equation 1 would infer that the following number of pits (P) were in use at each harvest. Using these values of P in equation 2 allows estimation of the total grain stored in pits (S) at each harvest. Substituting these values of S into equation 3 estimates the corresponding area (A) of arable under cereal cultivation. Population, as adult-equivalents (X), can be calculated from the proportion of the harvest (S) estimated as food-grain, and the adult consumption rate (c), as stated in equation 4. Overall balance in the model is tested by applying equation 5.

Gussage All Saints and Little Woodbury, also on the productive chalk-lands of Wessex, Conderton Camp on the Cotswold limestone, and Gravelly Guy on the gravel of the upper Thames valley, all appear to have been actively engaged in effective grain cultivation and storage, perhaps as smaller centres in their own right. The Park-Bowsings appears at the lowest end of the scale of production, as a very basic and self-contained farmsteading unit, of one or two families engaged in local subsistence agriculture which included only a few hectares of grain-arable, an impression borne out by large-scale excavation (Marshall 2007).

Checking mean values of the ratio S/A from equations 2 and 3, where it equals 3.0, as determined by the value of g, against those from equation 5, where it is 2.3, suggests a reasonable general balance within the model, given its over-simplicity and the level of approximation used throughout. Full agreement could be reached by

Pit capacity also tends to decrease with reduction in status of a site, reflecting the need to deal with harvests of different bulk. The exception is Gravelly Guy, the low mean volume there perhaps the result of other factors, such as the gravel substrate or distributed ownership of the crop.

adjusting estimates of g (here 3.05), r (0.115), and ks (0.05) accordingly.

Data from Conderton Camp (Thomas 2005) provide a good test for the model since here the pits are relatively well known, occupation was of restricted duration during the middle Iron Age, and traces of a well-defined field system survive. The good fit between the extent of arable for cereal production suggested by the model (2.3-4.6 hectares) and the known extent of an adjacent field system (3.6 hectares) suggests that the model provides a viable working outline for operation of pit storage, at least as a basis for further discussion.

Conclusions from the model -correspondence with general archaeological background Data obtained from the model, despite its simplified structure, clearly reflect the known social and economic background of these sites. Danebury, on open chalk-lands surrounded by other smaller settlements, can be viewed as a major centre of grain storage. It was capable of catering for a sizeable population, acting as a large defended centre with a considerable territory contributing to its resources and possibly dependent on it as a repository, as a focus for tribute, and centre for redistribution (Gent 1983; Cunliffe 1984; Cunliffe and Poole 1991).

The model for grain production and storage fits sites of such different types realistically in terms of projections for site population and extent of cereal cultivation suggesting that, as a first approximation and used with reserve, it may be more widely applied with some confidence to other sites, and to

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experimental Iron Age grain storage and so here, at least, the basic pit-based model may hold in unmodified form. Only one 4-post structure appears in the plan from magnetic gradiometry at Conderton Camp (Thomas 2005), perhaps suggesting that here also grain storage was predominantly subterranean.

consideration of site-specific samples of their pits. As far as the experimentation at The Park-Bowsings is concerned, the model helps further to define a basic system for pit-based storage in terms of possible numbers and types of pit in use per season, and is relevant to discussion of open and sealed storage systems.

It is of course possible to modify the model to include both types of storage-structure, but numerical data on the contribution of above-ground storage are simply not available. Hence the model presented here must be viewed as very preliminary and used as a general guide for discussion of unknowns, rather than a more detailed basis for exact calculation.

For the Park-Bowsings, a typical small farmsteading unit at the base of the Iron Age economy, the model suggests a grain harvest of 2-4m3 stored in 1-2 pits of mean capacity. Such a harvest could be divided between one medium sized near silo-pit, which retained the bulk as accessible food-grain, with the remainder as seed-corn, split between 2-3 smaller sealed non silo-pits, such sub-division providing some insurance against spoilage or other loss of contents. Analysis of pit size at further sites (FIGS 21-25) does suggest an approximate ratio between larger and smaller pits of about 1: 2-3. The larger pits, with any covering structures, were perhaps refurbished more intensively to allow a longer lifespan, and hence may appear to be under represented in the cumulative sample.

-the method of grain storage in pits ..small sites The model offers certain insights into the process of pit-based storage of grain, and suggests ideas for further archaeological and experimental testing. Analysis of smaller, simpler, more economically-autonomous sites, lying at the base-line of production, such as The Park-Bowsings, where a more direct connection between subsistence farming and consumption might be expected, provides a basis for consideration of larger, more complex sites. The pattern of construction and possible use of pits at such basic sites might form the simplest case for analysis, but one still containing distinct uncertainties.

-consideration of above-ground storage of grain The above model, as stated from the outset, refers only to grain storage in pits, and takes no account of reserves which may be held in any facilities above-ground, for instance in timber granaries of the type which may have been supported by 4-, and 6-post structures detected at many Iron Age sites, as at Danebury, Gussage All Saints, and Gravelly Guy. A range of functions has been suggested for these timber structures, including use as granaries, sheds, or rick-bases (Gent 1983; Stanford 1970; Ellison and Drewett 1971; Cunliffe and Poole 1991), and given this general uncertainty of use, let alone of lifespan, it is difficult to base any calculation on them with which to modify a model for storage based on pits alone. The balance between numbers of post-structures and pits appears to change through time at sites such as Danebury and Gussage, but because of surrounding uncertainty the significance of this in terms of grain storage remains unknown.

The model suggests that, for small farmstead sites, such as The Park-Bowsings, pit-based storage may have been the principal, if not the only method required. Here, a few pits would have been required each season to store grain, these were reused for a few harvests and then replaced. Given the need to divide the harvest of a few tonnes between seed-corn and food-grain, perhaps in the ratio of 1 to 4 or 5 respectively, corresponding sets of pits might be expected to form the basis for the total sample which accumulated at the site. Each variety of grain would of course require its own separate storage. The small pits suggested for seed-corn would only need to be broached for the spring sowing, and hence could remain sealed until use. Larger pits for food-grain would need to be accessed regularly, and hence ideally would remain unsealed but still fully-protected under a weatherproof cover. Such a facility for constant access would certainly be required at a small site, with the low consumption rate requiring at least one of the few storage pits to be open for protracted periods. The viability of this latter option was subject to testing by experiment at The Park-Bowsings, and compared with the performance of sealed pits, as outlined in the experimental section of this paper.

Estimates made at Danebury (Cunliffe 1984, table 100) suggest that, considering the total period of occupation, grain stocks may have been held equally in pits and above ground, and this would, in effect, double the values for storage capacity presented in this model, with a corresponding increase in projections for the area of arable and of dependent population, to levels which appear, from subjective assessment, to be excessive. However, no such post-structures were detected at The Park-Bowsings, a well-preserved complex, where such features would be expected to survive,

Given relatively small harvests of only a few tonnes, ensuring security of grain-stocks may have been

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experimental Iron Age grain storage settlement itself and other possibly dependent sites around it.

achieved at such simple undefended farmsteads by further splitting loads between smaller pits. This would help promote a lower mean value for pit volume at the site, as can be seen by comparing mean pit capacities at The Park-Bowsings with those at Danebury, Gussage, and Little Woodbury. Reserves may also have been held within huts for emergency use, in wicker hoppers or in sacks, and the known presence of very large storage jars, as at The Park, suggests an alternative container.

The suggested population was 6 households, estimated as about 34 people, cultivating up to about 17 hectares of arable. Using data from Butser for sowing rates, it was estimated that about 1 tonne of seed-grain would have been needed for planting the entire area of arable proposed, this requiring some 1.5 m3 of storage space, which would only amount to the contents of one medium-sized pit. Assuming that barley and wheat were sown separately, it was suggested that only 2-4 pits may have been in use at the site for storing seed-grain in any one year. Given an average wheat yield of 0.8 tonnes per hectare the arable was thought capable, over the longer term, of supplying about 60% of internal needs, with virtually no risk of famine, and of generating surpluses in about 80% of years.

..larger sites At sites which were larger than such small rather impoverished farmsteads, sites with higher productivity and perhaps acting more as centres for redistribution, a distributed, serially-accessible storage system would be required to cope with higher levels of grain. Two main storage-environments were available, the pit and the above-ground granary, of changeable relative importance. Covered but unsealed, ventilated pits, providing accessible, semi-subterranean grain-stores, would be intermediate between these two these modes.

These conclusions may be compared with those given in TABLE 12.

Given a batch of perhaps 50 to 100 pits storing grain each season at certain larger hillforts, such as Danebury, the majority of pits may have been sealed initially, and then broached in succession, moving a portable cover as required, to protect the opened pit. The model suggests that such pits would need to be covered rather than being emptied in a single operation. For instance, at Danebury, each of the 50 to 100 pits suggested by the model as required for a single harvest, of mean volume 2.7m3, would provide 1971 adult daily rations (given the value of 'g' adopted, 0.5m3/year). Each pit would therefore support about 50 adults for 40 days, or 200 adults for 10 days. Even for the briefer period the pit would certainly have needed covering, especially when stocks were required during winter and spring, wet and unpredictable seasons. It seems reasonable to suppose therefore that some were never sealed in the first place.

Section 2: EXPERIMENTATION BACKGROUND TO THE EXPERIMENTS AT GUITING POWER The sites at which experimentation was carried out The area in which the experimentation was carried out is located in the Gloucestershire Cotswolds (FIG 1), about 1.5 km NW of Guiting Power village (Glos., UK: SP 094 248). The site is located high on the dip-slope of the Cotswolds, between 170 and 200m OD, in an upland valley situation, sheltered by surrounding hills which rise around it to about 250m. Bedrock is well-drained limestone rubble, with superficial clay deposits. Experimentation was carried out within Iron Age ditched enclosures at The Park (SP 08325 25865), and The Bowsings (SP 08580 25865). These sites cover the gently sloping top of a narrow, steeply-sided spur, formed by the confluence of two headwater stream valleys of the River Windrush, a tributary of the upper Thames.

At sites acting as centres for bulk-storage, and lying within potential conflict-zones, fuller distribution of all reserves between a range of locations, from entirely accessible to well concealed, would have provided additional security over stocks. Alternative models A model for grain production and consumption has been proposed for the Iron Age settlement at Gravelly Guy (Lambrick and Allen 2004), incorporating arable and pastoral aspects, using elements of a more general economic model developed to describe subsistence farming in Central Europe (Gregg 1988). The main aim of this model was to examine the productivity of the arable economy at the site, and its capacity to sustain the

A brief summary of the Iron Age sites at which the project was based is given here, in order to set the experimentation clearly within its archaeological context (FIG 2). Small ditched habitation enclosures, usually rectilinear in plan and up to about a hectare in area, form a consistent feature of the Iron Age settlement pattern (5th/4th century BC to 1st century AD) in

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experimental Iron Age grain storage other larger sites, such as hillforts, where increased population and different organisation may have resulted in other practices. The Park-Bowsings is one such small settlement complex, and has been investigated in detail (Marshall 2007).

midland and southern Britain. They appear either in relative isolation or as part of a larger complex. Their small size makes such sites amenable to complete geophysical survey at high-resolution, and to extensive excavation, whilst their frequency enables comparative studies readily to be undertaken.

Pits: volume and shape of the sample from the sites -volume Levels of erosion are very low at both The Park and Bowsings, as shown by the survival of vulnerable features such as hut interiors and exterior hearths. Consequently, pits are assumed to be well preserved, with excavated depths and uppermost structure very close to those of the original features. The uneroded nature of these pits can be further demonstrated by comparing them with pits from the nearby Manor Farm enclosure (Saville 1979), where higher levels of truncation were encountered, and this can be quantified, suggesting that about 40cm has been removed from their tops by ploughing (FIG 16).

A group of such defended enclosures is being examined in detail by the author, in the northern Cotswolds, around the upper Windrush valley, mainly in the Guiting Power-Temple Guiting area (Glos., UK: SP 02/12). Typically, these sites consist of a ditched rectilinear enclosure, originally with stone-faced, clay-rubble, and timber rampart, accessed by a single gap entrance. The interior contains a small habitation zone, pit clusters, and some internal subdivision. Immediately around this main compound, lighter sub-enclosures, some containing pits, suggest a zone for working, storage, and other agricultural activities. Such sites also consistently include, within the main compound, a single relatively large rock-cut 'silo'-pit, set away from the majority of smaller, more typically-sized pits (Marshall 1999; FIGS 2, 20, 21). Examples of such silos are known from geophysical survey, have been verified by excavation, and are apparent from aerial photography at other sites not yet further examined. Such small sites provide a simpler format for analysis of Iron Age agricultural practices, located as they are towards the lower end of economic and social organisation. They form a basis for comparison with

Volumes of the 39 excavated pits from The Park and Bowsings form a distribution with a single peak, with no sign of any further division into sub-types (FIGS 10,11). Any division on the basis of volume is artificial, but reference to pits of non silo- (0.5-1m3, near silo- (1.5-3m3), and silo-type (>3m3) can be used to give some indication of relative size within the gradation (TABLE 13).

TABLE 13: Properties of excavated pits at The Park-Bowsings. mean number % of total diam.(m) depth(m) vol.(m3) non silo 1.20 near silo 1.60 silo 1.81

0.77 1.11 1.55

0.87 2.23 3.99

27 7 5

69 18 13

mean GSC (tonnes) A B 0.52 0.48 1.34 1.23 2.40 2.19

multiples of the basic non silo unit 1 2.6 4.6

Key: GSC: mean grain storage capacity, assuming that pits were for grain, as based on data (A) from modern grain (0.601 tonnes/m3) and (B) that assumed for iron age type (0.55 tonnes/m3).

type, are however noted as of considerable interest, because of the way in which they may imply accessible, covering roof-structures

Non silo-pits are the most common type, on average comprising 7 out of 10 excavated, with larger, near silo-pits less frequent, at about 2 out of 10, and the largest group, silo-pits, the least common, at about 1 out of 10. Simplifying the gradation of capacities, it is possible to suggest a basic unit volume, that of the non silo-pit, at the lower end of the range, with the far rarer silo-pit, capable of holding almost 5 times this unit volume, at the higher end (FIGS 20, 21).

Structures at the sites relevant to interpretation of pit function Grain storage pits are normally considered to have been sealed after filling, to remain so until broached and their contents brought into use. Structures encountered during excavation of pits at The Park-Bowsings, consideration of the physiology of grain storage, together with assessment of common-sense domestic and agricultural requirements, suggested strongly to the author that at least certain of the pits may not have been

-shape All pits are broadly cylindrical, with some of more open profile, with no basis for further sub-grouping. Those examples of stepped pits from The Park (FIG 21), again a minor variant on the standard cylindrical

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experimental Iron Age grain storage would have been placed out of the prevailing westerly winds. This leeward placement of entrances is also seen in circular huts at the site, and is typical of many others from the Iron Age in Britain, for similar practical reasons of increased shelter (Marshall: unpublished analysis; Feiller and O'Neill 1982; Parker-Pearson 1996; Oswald 1997).

routinely sealed, but rather were maintained under weather-proof covers. The following evidence from the study sites suggests the existence of covered, accessible pits: -stepped pits (FIG 21) Some of the pits at The Park bear a step-ledge, cut into the margin, as if to provide better access to the contents. Such stepped pits are an uncommon variant in the current archaeological record, but it should be noted that truncation from ploughing, common at many such sites, would remove any evidence for such steps, and that these features might have been more widespread than presently appears. Preservation at The Park in the area of these pits was excellent, with hearths and other internal features in the adjacent hut remaining intact. The existence of a step for these pits may be taken to infer that the contents remained accessible during storage, and hence would have been covered.

Certain other larger elongate pits, from other sites in the Guiting group of enclosures also show axial alignment NW/W to SE/E, as if indicating the windward placement of a former elongate cover (Marshall: unpublished data). -physical traces of covering superstructures A conical or tent-shaped thatched timber cover for a pit would have sufficient weight to rest in place without the need for many, if any, ground-fast posts or pegs, which in any case need not themselves have penetrated beyond the turf to leave any structural imprint. Physical traces of such covers in the form of postholes are not therefore to be expected. However, possible post-holes, arranged around a pit (F23) at Manor Farm (Saville 1979), a site near The Park-Bowsings, may indicate the former base of a cover or a protective fence, and if the latter then this might in itself imply the existence of a vulnerable and accessible pit-covering structure. Although badly truncated the surviving pattern of possible post-holes could indicate a rectangular cover, perhaps oriented end-on into the prevailing NW'ly wind.

-composite pit structures (FIG 21) Certain composite pit structures occur at The Park, as if intended for multiple storage of separate commodities. Occasional linked chains of pits appear to be entirely contemporary, forming unitary structures, and not representing intersecting pits of different dates. Cutting one pit into the fill of another would have caused potential problems for storage, from leakage of ground-water, could have been easily spotted during construction then avoided, and seems unnecessary given the ample space of intact bedrock available. These structures, if deliberately composite, could have stored several different commodities, with individual pit-elements partitioned, or may have formed a single, larger elongate unit. These features might again support the existence of covers, since sealing such larger openings would be rendered more impractical. However, there are many examples of re-walled intersecting pits from other sites, as at Conderton Camp (Thomas 2007). Similarly, at Danebury, some intersecting pits were separated from the fill of earlier pits, into which they were cut, using chalk blocks which bore traces of clay, perhaps caulking, suggesting that in these cases at least, infirm substrate was not an insuperable problem for successful operation (Cunliffe 1984).

The type of movable, prefabricated thatched roof for capping ricks, shown in use at the Butser Iron Age farm (Reynolds 1976, 20/ photograph 4), may give some indication of the type of cover proposed here as practical for weatherproofing certain grain storage pits. -linear arrangement of pits Clusters of pits often show clear evidence for structured layout. For instance, partial linear arrangements can be clearly seen amongst pits at The Park (FIGS 2, 21), Manor Farm (FIG 23), and Condicote Camp (FIG 25). Although not providing direct evidence for or against existence of a superstructure, such linear placement, especially of larger pits, would certainly render movement of any fairly heavy cover from one redundant pit to the next site far easier.

At The Park, a large, linear complex of adjoining pits produced evidence for two basal packings for sloping timbers, of a type suggesting supports for a pitched roof. This could have formed the basis of a very large roofed silo.

-consideration of farming practice and domestic usage of grain After the harvest, it would have been necessary not only to store the grain, but to divide it between seed-corn, to be saved for the next harvest, and food-grain for consumption. Setting aside the required quantity of all-important seed-grain as a closely-monitored reserve would seem more sensible than bulk storage of the entire stock and

-orientation of pit structures The stepped pits at The Park tend to show placement of the step on the south-eastern, leeward side, suggesting that any entrance to a hypothetical cover

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experimental Iron Age grain storage a solution might best be implemented from the start, using a fully proofed, tested, and accessible superstructure.

then using any uneaten remainder for sowing. The type of smaller, non silo-pit defined here could have held this reserve of seed-grain, whilst the larger pits held the remaining bulk more accessibly, for consumption. The ratio of 1:3 or 4 between mean volumes of the smallest and larger types of pit (TABLE 13) might reflect such division, 20-25% for retention, and 75-80% for more immediate use, a practical ratio.

In assessing features from The Park-Bowsings, other practical considerations argued for grain being held in accessible storage after the harvest: such grain could be constantly monitored against spoilage by ground-water, unexpected growth of mould, or incursion of rodents. Grain might also have provided an important item for barter, with the need to accommodate fluctuating reserves. Grain may also have been dispensed regularly to dependent households, with an obvious requirement for access to stocks. -silo-pits At many of the enclosure sites in the study-group a single larger type of pit has been clearly identified, further analysed by detailed prospection, and a selection of these have been excavated (TABLE 14; Marshall 1999). These silos are approximately cylindrical, rock-cut, about 2-3m in diameter, and originally some 1.5-2m deep. Several excavated examples come from sites which have suffered little erosion, so there has been negligible reduction of their depth by truncation from ploughing. These silo-pits are of too great a diameter to be simply and effectively sealed by such means as a weatherproof plug of wattle and clay, which would tend to sag, buckle, and split under its own considerable, unsupported weight, and would present major problems for intermittent access.

The reserve of seed-corn, which would not be needed until the following spring sowing, could have been sealed away in a pit. The bulk of the harvest, needed for consumption and exchange during the inter-harvest period, would have been better stored in a covered, weather-proof, but accessible pit. Food-grain sealed in a pit would have to be broached at some stage, perhaps during inclement winter weather, and this newly-opened pit would again require immediate emptying, or covering, this latter being the more sensible option from the outset. Assuming that large silo-pits were used for grain storage, and given a nominal capacity of about 3-5 tonnes, broaching contents for partial use would result in a major storage problem, and the opened reserve would represent an economically important deposit, not easily dispersed or consumed, and placed at risk of spoilage. Repeatedly resealing a pit with a caulked, clay-impregnated cover would seem an impractical option, and intervention with a temporary weather-proof lid would suggest that such

TABLE 14: Examples of silo-pits from Iron Age enclosures. Site

Parish NGR (SP-) mag. exc. size:max(m) vol. trunc. status (Glos., UK) diam. depth (m3) of site ------------------------------------------------------------------------------------The Park Guiting Power 08325 25865 * * 1.8 1.5 4 v.low F The Bowsings Guiting Power 08580 25865 * * 2.5 1.6 8 v.low S Manor Farm Guiting Power 08950 25000 * 2.5 1 >5 high M Middle Ground Temple Guiting 09180 27505 * * 3.0 1.6 11 low S Lot's Barn Temple Guiting 11320 27860 * ?4 ? ? ?high S Wharton's Furlong Cold Aston 13000 21580 * ?3 ? ? ?high M Key: NGR (National Grid Reference/ Ordnance Survey); mag (mapping by magnetic gradiometer survey); exc (excavated); trunc (extent of truncation by ploughing). Status of the site is as follows: F[armstead] of lower status and defensibility; S[tronghold] of higher status with defensive perimeter; M[inor ditched enclosure(s)].

sparse domestic debris.

Details of silo-pits, from sites in the study group, two of which have been excavated by the author (Marshall 1999), are as follows:

The Bowsings (FIG 22; PLATE 4) Excavation at the later Iron Age stronghold on The Bowsings, just downslope from the earlier farmstead at The Park, verified the existence of a silo-pit seen by magnetic survey lying isolated from the main pit cluster in the angle of the interior next to the single, small habitation area. Slabs which lay within the pit, near the centre of its base, may have retained the end of a central upright post, which could have

The Park (FIG 21; PLATES 2,3) A larger pit of silo-type lies amongst a group of pits close to a circular hut, in the corner of an annexe to the main habitation sub-enclosure, the latter full of pits, the former far less thus cluttered and perhaps representing select accommodation. After final use the silo was deliberately backfilled with rubble and

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experimental Iron Age grain storage 1976, 1978, 1979 1979a, 1987-1989, 1988, 1999; Bowen and Wood 1967; Hill et al. 1983; Fenton 1983; Martinek 1999).

supported the apex of a conical, covering roof-structure. When redundant the pit was deliberately infilled with rubble and sediment, without marked deterioration from intervening weathering, and its upper fill contained some scattered domestic debris. A deep pit, possibly for a large post, lay adjacent to the silo-pit, and may be associated, perhaps not as part of any superstructure but as a marker post or totem.

The experiments at Guiting Power are intended to extend this work to consideration of grain storage in rock-cut pits which remain unsealed but under a weatherproof cover. Sealed pits, of the type mentioned above, were included for comparative purposes, as controls.

Middle Ground The main enclosure at Middle Ground includes a silo-pit, located by magnetic prospection, situated in the SW corner of its interior. Excavation of this anomaly confirmed its status and size, and that once redundant it had been infilled with soil, rubble, and some domestic debris. There were no additional features detected within or immediately around the pit. A second large elongate anomaly, unexcavated, lies within a sub-enclosure just outside the main habitation enclosure and suggests another large pit-feature, perhaps with windward alignment.

Beyond general statement of the widespread proven utility of sealed pits for over-winter storage of grain, only those experiments carried out locally are outlined here in detail, these being from locations of similar topography and geology to Guiting Power and hence of direct relevance. The nearest experimental pits to Guiting Power, geopgraphically and in terms of limestone substrate were those carried out initially by Reynolds on Bredon Hill (Glos./Worcs: SO 93). Here, a set of pioneering experiments determined that barley could be stored successfully in cylindrical pits 1.22m wide and 1.37m deep, wicker-lined at the sides and with straw over the base, which were then clay-sealed for 26 winter weeks, during which over 40cm of rain fell (Reynolds 1967). Two similar pits were used, differing only in the moisture level of their load: one (the 'wet pit') contained 838kg of grain at 22% moisture, the other (the 'dry pit') 991kg at 14% moisture. On opening, the dry pit yielded 97% of its load as useable, with a 4.5% increase in grain moisture, with about 67.5% of its grain proving viable in germination tests. The wet pit preserved only 50% of its load, with none of its grain remaining germinable, but still edible. This suggested that grain must be below a certain moisture level before storage if it is to remain suitable for both planting and consumption. Carbon dioxide levels were determined within pits, and accumulation at 2-4% was noted.

Lot's Barn The main enclosure contains a large circular magnetic anomaly, marking a silo-pit just within an interior angle. Wharton's Furlong A small pentagonal enclosure forming part of the enclosure complex at the site contains an anomaly indicating the presence of a silo-pit. Manor Farm Rescue excavation just outside a ditched enclosure at Manor Farm, near Guiting Power, revealed a series of truncated pits, one of which (F6) was far larger than the norm, and was of better, more permanent construction, being finely lined with dry-stone work (FIG 12; Saville 1979). This considerable body of evidence suggested to the author the probable existence of covered, accessible pits at this type of site, forming a proportion of the total, coexisting with others which were sealed. It remained to simulate operation of such covered pits, assess their effectiveness for grain storage, and to compare their performance with that of sealed pits.

A second set of experiments followed on from this, and further examined the suitability of unlined pits for grain storage (Reynolds 1969). A pilot-test in the first set had already shown that 152kg of grain could be stored, with an increase in grain moisture from 15 to 24% over the 26 week period, and a recovery rate of 67% as viable or eatable. In this and in later unlined pits a self-sealing crust of grain a few centimetres thick was noted over the bare rock, forming a layer which acted to limit the deeper penetration of moisture into the bulk grain.

EXPERIMENTAL GRAIN STORAGE: existing work Since the 1960s many experiments have been carried out to determine the effectiveness of grain-storage in sealed underground pits, involving a variety of environmental conditions, rock substrates, pit forms, linings, and types of grain. The general success of such storage has been clearly established, and some of the practical problems associated with operation of this method have been determined (Reynolds 1967, 1969, 1972, 1974,

A further and larger unlined pit containing 1 tonne of grain at 15% moisture was broached after 15 weeks when 15% was removed before resealing, to test whether such access would adversely affect further storage. Up to this point the grain was germinable,

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experimental Iron Age grain storage but such viability ended during the remainder of its 26 week storage, when leakage of water into the pit caused 20% loss of grain, leaving the rest in fairly dry but musty condition. A smaller version of this unlined pit, containing only 152kg of grain, was more successful, with almost the entire load recovered in viable condition, depleted only by that forming a protective crust over the bare rock.

productivity, and hence of population. EXPERIMENTAL GRAIN STORAGE AT GUITING POWER (Glos., UK): analysis to determine the efficiency of covered, but unsealed silo-pits (FIGS 3-9; PLATES 1-4) General strategy Two seasons of experimentation were carried out after the local grain harvest, each running from autumn for 6 months, until the following spring. The timing and duration of storage was similar to that used by Reynolds (1967, 1969, 1974), starting in October, and ending in April. Iron Age pits of suitable size, back-filled with clay and rubble after their original use, which had already been excavated at The Park and Bowsings, were cleaned lightly to bring their internal surfaces back to fresh rock, and then used for experimental storage of grain.

Early work by Hill et al. (1983) at Butser Ancient Farm encountered problems with pit storage of barley, wet seasons causing moisture levels in outermost grain greater than 50%, with raised temperatures, carbon dioxide levels over 35%, and with germination rates under 5%. In more clement seasons pit temperatures were lower, less than 13oC, with levels of carbon dioxide also lower at below 25%, and germination rates of at least 90%. Beehive-shaped pits were found to be less wasteful of grain than cylindrical types because the narrower mouths of the former type were easier to seal well against ingress of rain and leakage of carbon dioxide from the pit. Amongst moulds developing on stored grain Penicillium species and members of the Aspergillus glaucus group were the predominant fungi found. It was concluded that because of the problems encountered in implementing reproducibly good storage that estimates of population based on pit numbers were likely to be unreliable.

Such grain storage experiments fit within the second of five categories of archaeological experiment outlined by Reynolds (1999), that concerning process and function. They fulfil the technical conditions and those of replication and reproducibility restated there. The initial hypothesis being tested by these particular experiments is that pits fitted with weatherproof covering structures but remaining otherwise unsealed, work better for storage of foodand seed-grain than do sealed pits.

These experiments indicated that, although practicable for storage, sealed pits were vulnerable structures, and that success of storage depended on skilled construction and observant maintenance, plus a measure of luck.

The general strategy of the project was to run all experiments under as adverse environmental conditions as possible, in order to test to the limit the practicality of grain storage in unsealed but weather-proofed pits against that in fully-sealed pits. At the outset of the experiment it was hoped that the ensuing winter period would be as inclement as possible, with high rainfall, wet ground, and driving wind creating potentially poor conditions for all underground storage of grain, lying against already moist rock and in contact with damp ambient air. Rainfall records for the area show that these conditions were indeed obtained for each of the winter periods during which experimentation took place (FIG 3; TABLE 17). To further stress the system, accessible pits were also left full throughout the test period. In practice it is likely that their contents would have been used progressively, and perhaps refreshed by addition, or even stirred to avoid stagnation, throughout the inter-harvest period, with only the final, residual contents experiencing maximum exposure for the entire period.

The general conclusions drawn from the subsequent series of grain storage experiments, centred on the programme of research at Butser Ancient Farm, have been briefly restated recently by Reynolds (1999, 159) as follows: A series of experiments over 15 consecutive years have shown that grain storage in sealed pits is entirely practicable, with an efficiency dependent on a limited range of environmental variables. Failure of storage is caused by decomposition, as promoted by the accelerated life-cycle of micro-organisms endemic to the grain being stored, or to water penetration. Importantly, work demonstrates that storage of seed-grain is possible, and that this grain retains an average germinability greater than 90%. It was also noted that the pit has an effectively unlimited life, and can be regarded as a passive, reusable container, this tending to invalidate any clearly-defined basis for estimates of arable

Details of the pits which form the basis for these experiments are as follows (TABLE 15):

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experimental Iron Age grain storage TABLE 15: Properties of pits used for experimental grain storage at The Park-Bowsings. pit depth diam. (m) (m) experiment 1 1 0.7 1.2 2 0.7 1.3 3 1.2 1.5 experiment 2 5 1.3 1.4 experiment 3 4 1.7 2.3

depth vol. :diam. (m3)

V

E

type

grain straw (tonnes)lined

sealed

0.58 0.54 0.80

0.79 0.93 2.12

0.30 0.32 0.24

0.21 0.22 0.29

non silo non silo near silo

0.55 0.66 1.30

no yes half

yes yes no

0.93

2.00

0.21

0.28

near silo

1.38

no

no

0.74

7.06

0.25

0.43

silo

4.85

no

no

Key: V (venting factor) and E (exposure) are explained in the section 'Basic statistics used for analysis of pit groups', with further details given in FIG 18.

carry thermocouples for remote measurement of temperature, and tubing for periodic analysis of carbon dioxide and water vapour within the stored grain. A separate thermocouple was also inserted 30cm into the basal bedrock, in order to log ground temperature. Thermocouple wires and plastic tubing were bundled, and their ends housed in a weatherproof port at the surface. A port was also provided for removal of small grain samples by probe, in such a way as not to disturb the internal atmosphere, which remained sealed. No fixed instrumentation was placed in the accessible, covered pit, since direct measurement and sampling were possible.

EXPERIMENT 1: operation of sealed pits 1-2 (smaller, non silo type), and of covered pit 3 (near silo type), at The Bowsings (FIGS 4-7; PLATE 1) Objectives During autumn 1993 to spring 1994 the main experimental objectives were -to determine the general problems and effectiveness of pit-based grain storage within the local type of limestone rubble bedrock; -to refine instrumental methods; -and to compare the efficiency of two sealed pits against that of an unsealed near silo-pit set under a weatherproof cover, this latter being partly-filled, acting as a trial for fully operational silo-pits.

Loading and proofing of pits Pits were further cleaned and maintained, to be as dry as possible immediately before loading grain. Grain (untreated organic-grade milling wheat: variety Estica, at 15.3% moisture level, as harvested) was loaded into prepared pits, at capacities given in TABLE 15.

In order to determine whether pit-based storage was more effective if the contents were protected from damp rock at the sides and base, one of the sealed pits (pit 2) was lined as well as covered with about 7 packed centimetres of dry straw before filling with grain, whilst the other sealed pit (pit 1) was covered with straw before capping, but left otherwise unlined. These two sealed pits were cylindrical and of typically smaller size, about 1.3m in diameter and 0.7m deep, similar to those used in experimentation on Bredon Hill (Reynolds 1967, 1969).

Before sealing, pits 1 and 2 were ringed at the top edge with large limestone blocks to provide additional protection, then covered with about 7cm of packed straw, sealed with 15cm of Lias clay, topped with a wooden cover, and finally covered with 25cm of turf. The multi-layered capping was penetrated only by the two re-sealable sampling ports, one each at the centre and edge of the pit, which were required to enable periodic gas analysis and removal of grain by sampling tube for determination of its moisture level. The capping was thoroughly sealed around the edges of the pit, and where instrument pods penetrated, adding further applications of clay as required.

The final near silo-pit (pit 3), which was not sealed, but left open under a cover, was divided into two halves, one similarly straw-lined to sealed pit 2, the other left unlined. This covered pit was similar to pits 1 and 2 in basic cylindrical shape, but was larger, at about 1.5m diameter and 1.2m depth. Preparation and instrumentation of pits Excavated surfaces within rock-cut pits were lightly scraped to remove any last traces of fill, returning the rock-face to as natural a condition as possible. In the two pits to be sealed (pits 1 and 2), metal pods were driven vertically into the base, one at the midpoint, with a second 7cm in from the edge, to

The unsealed pit was covered with a ridged frame of lashed timbers, thatched on all but the leeward, entrance side, this latter formed by suitable timber-work. Space inside this cover was used to hold two further tests: small-scale simulation of

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experimental Iron Age grain storage above-ground storage in a weather-proofed granary, and hut-based storage in sacks.

whilst the pit remained sealed and in essentially undisturbed operation. Any materials introduced into the pit were carefully cleaned and of non-toxic type, not affecting the microbial population.

Monitoring of the experiments All experiments were fully monitored throughout their duration, with conditions in the external environment and within the pits being recorded at appropriate intervals. Instrumentation was placed in each pit, suitably coupled to be read remotely from the surface

The following data were recorded on a daily basis, around noon, and used to calculate weekly means (TABLE 16):

TABLE 16: The regime of data recording. parameter measured as when logged -------------------------------------------------------------FOR THE ENVIRONMENT (FIGS 5, 8): rainfall totals for the area weekly temperature air extremes at the site daily rock current value at the site daily humidity current value at the site daily wind direction summary daily WITHIN PITS (FIGS 6-8): temperature current value at the site water vapour cumulative value carbon dioxide cumulative value grain moisture cumulative value general condition current

daily weekly weekly weekly daily

milled, compressed blocks in a Grainmaster protimeter calibrated against standards and set on automatic compensation for temperature.

Environmental air temperatures were recorded at the site of the experiments by accurate bulb thermometers. Temperatures within pits were read by digital thermometer (Comark 1, re-calibrated against accurate standards), connecting it to the fixed thermocouples.

The condition of the pits was also recorded, including evidence of any leakage or depredation by rodents. Given the absence of any such problems no remedial action was ever needed.

Levels of carbon dioxide and water vapour were analysed by drawing samples from within the pit through a reactive 'Drager tube' using a proprietary hand-pump, then reading the result as a colour change (Leichnitz 1982 and 1983). Water vapour was determined by a Drager tube (label: 'water vapour 0.1 CH 23401: range 0.1-40 mg/litre'), in which water reacts with selenium dioxide and sulphuric acid to give a reddish/brown product. Tube readings in mg/l were converted to percentage relative humidity, using tables given in Leichnitz 1982. Levels of carbon dioxide were determined using another type of Drager tube (label: 'CO2 0.1%/a CH 23501'), in which a reaction with hydrazine, using crystal violet as redox agent, gives bluish-violet carbonic acid monohydrazine as colour indicator. The pits were allowed to equilibrate for a month before the initial gas-vapour readings were made.

Experiment 1 validated methods and instrumentation, as well as providing basic information on the satisfactory performance of sealed pits and a pilot version of an unsealed but covered pit, these latter data essential for planning a fuller version in Experiments 2 and 3. EXPERIMENT 2: operation of a covered, unsealed near silo-pit using an elongate cover, at The Park (FIG 8; PLATES 2,3) During the autumn of 1994 the second stage of experimentation was started: operation over six winter months of a near silo-pit, larger than that used in Experiment 1, maintained under a thatched weatherproof cover, all constructed from local natural materials. Preparation and instrumentation of pits A large rock-cut silo-pit (pit 5) 1.3m in diameter and 1.4m deep, which had already been excavated, was cleaned for experimental reuse. Given that stored grain remained accessible for purposes of sampling and environmental monitoring, a simplified set of fixed instruments was required. Before filling the pit,

Samples of grain (about 5g) were removed from the centre and edge of sealed pits 1 and 2 through re-sealable gas-tight ports, using a specially designed grab-tube, all done without disturbing internal equilibrium. Moisture content of grain was immediately determined by measuring conductivity of

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experimental Iron Age grain storage at weekly intervals, using samples from the centre and from four cardinal points 15cm from the margin, to provide a mean. Movement of the air under the cover was monitored by smoke-trailing, and the existence of efficient, slow, down-wind venting of the interior was established.

a thermocouple was placed 30cm down into the limestone bedrock which formed the base of the pit in order to measure rock temperature, as was done for all previous experiments. Temperatures within the grain load were determined by thermocouples inserted at the time of reading, not fixed. Gas analysis was not required to be carried out within the grain-load, since there was continuous ventilated exchange with the normal atmosphere under the cover. Grain was sampled using the same insertable grab-tube used for Experiment 1.

The final state of the pit and its contents At the end of experimental work the covering structure was removed and the condition of the pit and stored grain was examined. The appearance of the surface of stored grain was noted and the pit was emptied, leaving in place for further examination the thin crust of grain adhering to the sides and base.

Loading and proofing of the pit The pit was filled with 1.3 tonnes of untreated modern organic-grade barley at 16.8% grain moisture. The top of the pit was edged with a ring of large stones and the opening covered by a set of light loose-fitting timbers placed in parallel and which were easily removed to give access to the surface of the grain. A timber-framed cover had been prepared near the pit, for placement after the pit was loaded. This ridged tent-like cover was rectangular in ground-plan with a rounded back-end and with an entrance in the front upright end. The frame was constructed of hazel limbs, and was 4.5m long, 2.7m wide, and 1.3m high. This cover was placed over the pit, with its rounded back-end into the prevailing westerly winds and the upright front with its low door was aligned towards the leeward side, to be further sheltered by a gable-extension of the roof. The entire structure was suitably thatched over sides and back, down to a base-course of stones which held the ends of thatching-straw away from the damp ground. The facing of the entrance-end was formed from closely-spaced light hazel timbers, lashed to leave a grille of intervening gaps for aeration of the interior. The cover fitted the pit well in plan at the sides, leaving sufficient gap laterally as a buffer against outside weather. Its length left some extra space at the front, useful for comfortable access, and at the rear of the pit to provide an area with potential for general storage.

EXPERIMENT 3: operation of a silo-pit (pit 4), using a conical cover, at The Bowsings (FIG 9; PLATE 4) During the autumn of 1996, grain storage was monitored in a covered silo-pit, similar to that provided for Experiment 2, similarly thatched, but this time conical and supported by a central post. Again, this experiment was carried out in an excavated feature, a large silo-pit, with slabs remaining at the centre of its base which suggested packing for a central post supporting the apex of a roof. All methods used in this experiment were the same as for Experiment 2, and both experiments produced very similar results, with each type of cover providing excellent protection for stored grain. RESULTS FROM EXPERIMENTS 1-3 Data from Experiments 1 and 2 are given in some detail, with those from Experiment 3 closely similar to and validating those of Experiment 2. The external environment -rainfall at the site of the experiments (FIGS 3, 5, 8; TABLE 17) Rainfall records for the Guiting Power area over the years 1974 to 1996, the 20 year period before the experiments, show an annual maximum of 9.9cm, a minimum of 5.7cm, and a mean of 7.68cm (s.d. 0.97). Annual rainfall for 1992 and 1993, the years before Experiments 1 and 2, at 10.1cm and 8.7cm respectively, was higher than the longer-term mean, resulting in ground conditions sufficiently moist to provide relatively adverse conditions for ground-based storage of grain, the preferred option. During the experimental periods themselves, conditions were equally testing, with higher than normal rainfall for the duration.

Monitoring the experiments With the exception of carbon dioxide and water vapour assay, the same regime of recording and sampling was carried out as for Experiment 1 (TABLE 16), allowing a week for equilibration of the loaded and covered pit to take place before the first readings were made. Temperatures were measured for bedrock, stored grain, and air, both externally and under the cover of the pit. Grain from mid levels in the pit was assayed for moisture content

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experimental Iron Age grain storage TABLE 17: Rainfall at the site during experiments. values for stated RAINFALL (cm) months (0: start of expt. 1 expt. 2 expt.) ------------------------------------------------before totals -1 to -3 19.2 25.7 expt. -1 to -6 45.6 35.1 cumulative 64.8 60.8 period

means/ -1 to -3 6.4 8.6 month -1 to -6 7.6 5.9 ------------------------------------------------during totals +1 to +3 30.6 30.9 expt. +1 to +6 49.2 38.6 cumulative 79.8 69.5 means/ +1 to +3 8.2 10.3 month +1 to +6 10.2 12.9 -------------------------------------------------air temperature and humidity (FIGS 5, 8) For Experiment 1, minima for the period varied between -2 and 4.7oC (mean 1.5, s.d. 2.0). Maxima varied between 2.7 and 13.8oC (mean 7.4, s.d. 2.8). Relative humidity of the air external to the experiment varied between 46 and 85% (mean 72.5, s.d. 10.6). For Experiment 2, minima for the period varied between -9 and 5oC (mean -0.9, s.d. 3.2). Maxima varied between 8 and 27oC (mean 16.0, s.d. 6.4).

8) For Experiment 1, temperature of the bedrock underlying pits ranged from 5.4 to 10.7oC (mean 8.3, s.d. 1.5). For Experiment 2, temperature of the bedrock ranged from 9 to 15oC (mean 10.8, s.d. 1.5). Conditions within pits -temperature of air around the grain (FIGS 6, 8; TABLES 18,19) For Experiments 1 and 2 temperatures were as follows (TABLE 18):

-temperature of bedrock underlying pits (FIGS 5,

TABLE 18: Air temperature within pits in Experiment 1. Note Temperature (oC) Pit min. max. mean s.d. ---------------------------------------------------------Sealed pits 1 mid 3.4 15.4 10.3 3.5 unlined edge 4.5 14.9 10.4 3.1 2 mid 3.4 15.2 7.6 3.5 straw lined edge 1.3 22.4 9.2 5.6 Unsealed, covered pit 3 air -2.1 12.8 6.2 4.1 air under cover 3 unlined 2.8 10.3 6.6 2.0 lined 2.4 11.3 6.9 2.1 Simulation at small scale within pit 3 of: granary hut -3 13 5.7 4.0 sack storage -3 12.9 5.6 4.1 TABLE 19: Air temperature within the pit in Experiment 2. Temperature (oC) Note Pit min. max. mean s.d. ---------------------------------------------------------air min. -9 5 -0.9 3.2 air under cover max. 8 36 16.4 7.2 air under cover grain min. 2 17 7.0 3.5 max. 6 19 10.0 3.4

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experimental Iron Age grain storage of 2.21%, and s.d. of 1.9. Levels in lined pit 2 ranged from 0.07% to 0.18% (2 to 6 times the normal atmospheric level of 0.03%), with a mean of 0.11%, and s.d. of 0.04.

-relative humidity of air around the grain (FIG 6) Levels of water vapour were recorded for the sealed pits in Experiment 1 only; checks for unsealed pits verified levels close to those of the general atmosphere. In unlined pit 1 levels increased from 8.6% to 22% (mean 13.6%, s.d. 4.6) from sealing to broaching, and levels in lined pit 2 increased from 12% to 22% (mean 16.7%, s.d. 3.5).

Levels in the unlined pit rose steadily, but in the lined pit the level rose at a third of this rate, representing a difference in respiration rate of either the grain or of the microbial contamination.

-carbon dioxide content of the air around stored grain (FIG 6) Levels were recorded for the sealed pits in Experiment 1 only. Checks within bulk grain in unsealed pits verified levels close to those of the general atmosphere. In unlined pit 1 levels ranged from 0.15% to 4.80% during storage (5 to 160 times the normal atmospheric level of 0.03%), with a mean

-moisture content of the grain (FIGS 7, 8; TABLE 20) For Experiment 1, grain moisture increased steadily within sealed pits 1 and 2 but held far closer to its original condition in unsealed pit 3. Grain stored under the cover of pit 3, in a lagged container, simulating an

TABLE 20: Levels of grain moisture for Experiment 1. % moisture content (15.3% at start of expt.) Pit min. max. mean s.d. Note ---------------------------------------------------------Sealed pits 1 mid 16.4 19.2 17.7 0.9 unlined edge 16.6 18.7 17.8 0.6 2 mid 16.2 18.9 17.9 0.8 lined edge 16.5 22.6 19.1 1.9 Unsealed pits 3 lined 15.6 17.2 16.7 0.4 unlined 15.3 16.9 16.3 0.5 Simulation at small scale in pit 3 of: granary hut 15.3 18.0 17.0 0.7 lagged sack storage 17.3 21.4 19.2 1.3 unlagged long had sprouted around this edge after 6 weeks, reaching about 12cm long after 18weeks, but always remained sparse, etiolated, sickly, and dying back. This growth was curbed by adding more light-proofing timbers over the mouth of the pit.

above-ground granary, also kept within a few percent of its original moisture content. Grain stored in the same place, but unlagged and subject to closer contact with damp air, simulating sacked storage, showed a rise in moisture over the period which was similar to that observed for the sealed pits, but less steady and subject to larger fluctuations.

-final condition of the grain The success of storage was gauged in terms of any decrease in its general condition, and viability as seed. Degradation by microbial, insect, and rodent activity, was determined from its appearance, smell, palatability for humans and stock, and further examined by detailed microscopic analysis. The absence of harmful microbes, and of mycotoxins (Lacy 1972) was established in microbiological culture. The ability of grain to germinate after storage was measured against standards.

For Experiment 2, the moisture content of grain held very steady between 16.3% and 17.6% (mean 17.0%, s.d. 0.3), close to its original value. -condition of the pits during storage In Experiments 1 to 3, all pits performed faultlessly, with no failure of weather-proofing structures nor damage to stored grain from seepage of ground-water, decay, or attack by rodents.

The bulk condition of grain in both sealed and unsealed pits remained excellent and relatively unchanged in appearance over the 6 month period of storage, fully palatable for human consumption, and viable as seed-corn. At the end of storage the musty smell from fungal growth was more pronounced in sealed pits but still slight, and in all pits

In Experiments 2 and 3, weak levels of light which penetrated the covers, combined with moister conditions at the uppermost interface between rock and stored grain, resulted in slight premature germination of some grain. Seedlings about 4cm

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experimental Iron Age grain storage rates for stored grain against those for retained control samples of grain, kept dormant under ideal indoor conditions (TABLE 21). About 1000 grains from each source, were sown separately on peat in seed trays at room temperature (7-24oC) for 7 days, watering every 2 days, after which time the number of grains germinating to a stated decimal growth stage were noted (Tottman and Broad 1987). During the period of the trial seeds germinating to between stages GS5 (with radicle emerged from the caryopsis and longer than 1.5mm) and GS9 (with leaf appearing at the coleoptyle tip) were logged as viable.

visible mould was only present where grain was in direct contact with damp bedrock (PLATE 3c). Such rock surfaces became covered by a crust, about 3-4cm thick at most, the inner zone of which consisted of about 1cm of rotted, germinated grain, lying against the rock itself. This spoilt grain was separated from bulk grain by about 2-3cm of damper, fused, slightly musty, but ungerminated grain. Only a small fraction of the stored grain was in this damaged condition (3-5%), but even this could have been used for stock-feed, leaving the rest for consumption or planting. The viability as seed of grain stored in pits for 6 months was checked by comparing germination

TABLE 21: Viability of stored grain from Experiment 1. source grains germinated to of grain GS 5-9 GS 30%, and inhibits further germination, causing grain to enter unstable dormancy. This instability is caused by micro-organisms which can survive such conditions, but under the lower ambient temperatures induced by surrounding rock their life cycles are inhibited. Such pits are therefore ideal for storage if sealed effectively, often with losses of less than 2% in 1.5 tonne storage and grain viability over 90%. The following technical comments apply: -All dormancy is by its nature unstable, and is induced not within the pit but during the period of pre-storage drying, to be broken by increased moisture, heat, and light;

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experimental Iron Age grain storage grain, with levels of such pests probably minor and inactive anyway in clean, screened grain. Low levels of such inevitable contamination would have been more acceptable in prehistoric agrarian economies than modern. Medium to high levels of carbon dioxide would do little to stop marginal depredation by any mammals, birds, or insects from the outside, a reduced problem since many of these populations would be at lower levels during the winter storage period, and such pests would anyway introduce their own aeration on entry.

-the micro-environment of the storage pit The critical factors for maintaining dormancy and viability in stored grain are suitably low levels of moisture and of heat, with absence of light then becoming important. Kept dry, cool, and aerated, clean grain can be maintained in viable condition without significant loss for years, in either sealed or unsealed storage. Problems arise however when an attempt is made to store grain in a structure such as a rock-cut pit which, although relatively cool, is semi-permeable, with internal surfaces permanently damp from condensation of outgoing metabolic water from the grain and incoming moisture from the ground.

Sealed storage of unventilated grain, perhaps only weakly dormant and imperfectly dried, held in contact with damp rock surfaces for periods of several months, and not amenable to periodic inspection is therefore to be viewed as a relatively high-risk strategy for storage of essential reserves, especially if it is the principal method employed, even given the undoubted skills of the Iron Age farmer.

In a sealed storage structure, increasing moisture from rock walls first hydrates the surface of any dry organic material to levels which permit the development of moulds. These begin to flourish in humidities over 70%, mainly on finer particulates such as dust and chaff rather than initially on the grain, this process contributing further metabolic water and heat to the stored bulk. Developing convection currents then disperse these slightly warmer humid conditions more widely within the pit, especially to upper layers, and promote development of moulds and bacteria. Gradients of temperature, carbon dioxide, and final quality of stored grain noted in pit storage (Reynolds 1974, fig. 3) can be interpreted by this mechanism.

An effective method for grain storage in pits The set of experiments at Guiting Power demonstrates that efficient grain storage in rock-cut pits can be achieved under sealed, and especially unsealed but weather-proofed, conditions. It is possible to rank pits in order of effectiveness for grain storage, taking all aspects of the process into consideration. In terms of maintaining its grain-load in dry, uncontaminated condition the unsealed, covered type of larger pit was certainly the most effective (Experiments 2 and 3), with the added advantages of being able to monitor, and access its contents. Less effective was the type of unlined, sealed pit, and less still was the pit which was both sealed and straw-lined (Experiment 1). Better than any of these methods, in terms of final quality of the bulk grain, would be above-ground granaries, if fully weatherproof and caulked to retain grain but allowing sufficient aeration of the interior.

The softened surfaces of grain and other organic material are then rendered more amenable to combined microbial attack, at first involving aerobic microbes, with anaerobes becoming more important as partial anoxia develops. Decomposition of grain takes place more fully against the damp rock walls, within a crust which acts to absorb moisture sufficiently to contain advanced decay within a few centimetres at the edge of the stored bulk (PLATE 3c). This adds some moisture but little metabolic heat to the system, the rock acting as a heat-sink, and contributes much of the carbon dioxide to the interstitial atmosphere. The extent to which this process can develop is held in check by maintenance of low temperature. Ground temperatures, lower and more stable than those of the external air, the effectiveness of the massive rock substrate as a heat-sink, and the low thermal conductivity of both rock and air, all serve to maintain appropriately cool conditions. Increasing the stored volume would also act to even out any fluctuations in environmental conditions, with the added bonus of decreasing relative exposure of stored bulk to damp rock.

Use of caulked wicker linings with a marginal air gap within pits would be expected to produce better results than those of lighter and less open material such as straw lying in direct contact with rock. These latter act to hold moisture at the grain-rock interface, also reduce the effective volume of the pit, and could unnecessarily introduce a further range of micro-organisms which might cause increased rotting and contamination by mycotoxins when damper conditions developed. The grain, unlike over-absorbent straw, serves to form its own self-sealing crust over rock surfaces, which is effective in protecting the remaining bulk of the grain, but at the cost of loss.

Semi-anaerobic conditions within the pit would do something to suppress further development of any insect infestations already present on the grain. Any such proliferation is usually more pronounced in damper, softer organic contaminants than in harder

Whilst sealed pits work because they act to keep water out, they also act to retain it, as seen by the

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experimental Iron Age grain storage environmental damage from inclement weather, fire, or theft.

increased moisture content of trapped air and condensation over the underside of the sealing layer. Allowing ventilation through the surface of the bulk grain at the top of the pit prevents any such build-up of moisture, and achieves stable, low levels of grain moisture, even under external conditions of heavy winter rainfall. In operational terms, such storage in accessible, covered pits falls between that in sealed inaccessible pits, and that in fully ventilated accessible above-ground granaries, combining certain advantages of both.

IRON AGE PITS AND THEIR USE FOR GRAIN STORAGE Overview The evidence for use of such pits primarily for grain storage comes from a combination of indirect sources: classical writers, ethnographic parallels, archaeological inference, and importantly by the way they fit well into simple ergonomic models for cereal cultivation, land-use, and population density. Additional support is lent by the difficulty of proposing an alternative use for such pits, given their high numbers and currency over a range of sites of differing type and social use, and their frequent absence from sites located in areas unsuitable for arable agriculture. Certain similarities of form within and between pit groups, as indicated by key statistics, also suggest a common basic application.

Pests of grain The grain weevil (Sitophilus granarius), the principal grain pest known in Roman Britain, becomes active at about 11% moisture and at temperatures around Reducing moisture by drying to levels 15oC. non-destructive for grain and maintenance at lower temperatures would hence deter insects (Morris 1979, 6). Reducing both of these factors in a well-ventilated covered pit would act directly to suppress insect activity.

Previous experimentation has certainly shown that over-winter grain storage is possible in rock-cut pits, but has over-emphasised the need for sealing as a physiological requirement for success. Simulations at Guiting Power have extended research based on sealed pits to include unsealed but weather-proofed alternatives, which have been shown to operate better in terms of the quality of stored grain and which confer a series of other advantages stemming from accessibility to stocks. Use of such covered pits, especially of larger 'silo'-type, is suggested during the Iron Age as part of a range of grain storage facilities which also included fully-sealed pits and above-ground granaries, in proportions which are likely to have changed over time and between different types of site according to circumstances. It is proposed that such diversification was prompted largely by the need for insurance against failure of storage under poor environmental conditions and by the possibility of theft, damage, or destruction of essential stocks by enemies. It is otherwise difficult to find an explanation as to why pit-based storage, characteristic of the mid to later Iron Age in southern Britain, ever became widespread in such areas of higher rainfall and damper ground conditions, when other better alternatives appear obvious.

Threshability of grain Grain, when dried by natural means or by brief scorching can be more easily threshed and confidently stored in prime condition. Certain cereals, such as emmer and spelt, require this treatment before further effective processing (Morris 1979, 8). A DIVERSE STRATEGY FOR STORAGE It seems likely that a mixture of these three main storage methods, sealed, semi-sealed or covered, and above-ground were in use as follows, with the emphasis on appropriate dispersion of reserves and insurance against various risks: Dispersed, concealed reserves in small, sealed pits for key stocks of seed-corn, stored for the few months between harvest and spring sowing, concealed for security, and with several in use, including replicates and those for different crops, damper internal conditions perhaps keeping the grain primed for planting; Larger, briefly sealed pits for secure, concealed food-grain reserves, broached serially over the inter-harvest period, emptied completely and contents relocated or covered and the contents removed as required;

Analysis of Iron Age pits -validity of data (FIG 16) There are many examples of pit groups from Iron Age sites in southern Britain, and although these provide sufficient data for comparative analysis, there is usually some doubt as to their state of preservation, and whether any truncation which they may have experienced can be quantified. From consideration of the site and its previous land-use it is possible to identify the more intact pit-groups, and to retrieve useable data from damaged pits. Such initial processing is essential before any further analysis

Accessible reserves -larger, unsealed pits covered by a superstructure from the outset containing accessible stocks for consumption and trade in a rock-protected, semi-subterranean environment; -above-ground granaries also containing accessible stocks for consumption and trade, removed from damp rock, but more vulnerable to

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experimental Iron Age grain storage have been divided in the ratio 1:4, into about 20% retained for seed-corn, and 80% as food-grain, each to be stored separately and accessed differently. If this was the system used then two paired populations of pits might accumulate as a result. Small, non silo-pits, the commonest type, could have stored seed-corn, with effective capping of their smaller aperture at ground level being entirely practical. Larger pits, at about four times this volume, of at least near silo type, could have taken the bulk of food-grain, which perhaps remained unsealed and accessible under covering roofed superstructures. Successive pairs of newly-constructed pits would tend to maintain this general 1:4 ratio of volumes, but would vary in size according to the requirements of the harvest, larger in some years than others, resulting in two interleaved sub-populations, each varying in capacity about its own notional mean. Any such basic process would be further complicated by, for instance, splitting larger loads of food-grain between several smaller pits, perhaps for reasons of security or through divided ownership, these pits then appearing amongst the smaller sub-group. Differential reuse of pits would also complicate the pattern of their accumulation. Larger pits, representing a significant investment of time and perhaps bearing some covering superstructure, may have been cleaned rather than readily abandoned. Small pits for seed-corn might have been replaced far more readily, not just because this was easier, but deliberately in order to avoid microbial cross-contamination of a crucial reserve. Again, small pits may have been converted into larger pits by repeated cutting back, again distorting the original strategy for pit construction.

can continue. Examination of data on depths and diameters of pit-groups, establishment of regressions summarising the relationship between these dimensions, and comparison against standards, can go some way towards providing a measure of quality control between pit groups (FIG 16). Differences between regression lines of depth against diameter for pit-groups can also help identify significant differences in form, of possible interest to discussion of function (FIG 17). Pits from Iron Age enclosures on valley gravels, in the upper Thames basin, for instance, tend to be relatively shallow compared to those on upland limestone (examples: Lambrick and Robinson 1979; Darvill et al. 1986; Allen 1990; Allen et al. 1993; Bateman et al. 2003). It should however be noted that in some areas shape may result from necessity rather than considerations of function, for instance the softer nature of the gravels might require pits to be shallower to avoid collapse at the sides. -consideration of volumes (FIGS 10, 11) The range of volumes, plotted as a histogram of frequencies, shows relatively little variation between different pit-groups. There is a single maximum at around 1 or 2m3, followed by a continuous decrease in frequency, with very few pits larger than about 8m3. The position of this maximum frequency can change between sites, being about 1m3 for The Park-Bowsings and Little Woodbury, and about 2m3 for Danebury and Gussage All Saints, reflecting differences in preferred capacities. There is no basis for dividing the range of volumes into any clearly-defined sub-groups, although these could lie hidden within the general distribution. The least that can be said is that pits from different ends of the size-range are likely to have had different functions within grain storage. Any terminology relating to size must therefore be for convenient reference rather than denoting distinct sub-types. In this analysis the following terms are applied to pits, to denote the general gradation of volume: 'non silo' (about 0.5-1.5m3), 'near silo' (about 1.5-4m3), and 'silo' (>5m3) (FIGS 10-11). It should be noted that, in this paper, and in Marshall 1999, the term 'silo' is used to indicate a pit of larger size rather than storage pits in general, as for instance in Reynolds 1999.

Despite these complications, on the basis of the system of paired pits suggested above, it is possible to simulate frequency distributions of accumulated pits which fit the skewed ranges of the actual data well (Marshall: unpublished analysis) (FIGS 10-11). It is possible to distinguish these three types of pit, non-, near- and full silo, in the archaeological record at various sites, and examine their spatial relationships (FIGS 21-25). The final distribution of pits at a site usually represents a complex, superimposed accumulation of isolated and intersecting features, established over a considerable period, often within a discrete area set aside for the purpose. Within such pit-groups it is difficult to establish a precise succession of individual pits since linking stratigraphy is usually lacking, and dating evidence from pit-fill is too imprecise to allow other than very general sequencing. This means that it is rarely possible to discuss relationships between these specific types of non silo, near silo and silo-pit, and examine any case for patterns of use.

A case could be made for scaling these size-related terms in a more relative manner, according to the type of site. What might have constituted an adequate silo at a small farmstead may well not have been sufficient for this purpose at a large hillfort, with its greater storage requirements. In the ergonomic model for grain storage presented in this paper, it was suggested that the harvest might

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experimental Iron Age grain storage irregularly pentagonal ditched enclosure (Wainwright 1968). Here, pits are concentrated in the western half of the enclosure, ranged around the hut in three fairly discrete groupings, at the N, W, and E (FIG 24). Three silos lie in the N grouping, with all groupings containing a mix of near- and non silo-pits. Some concentration of silo-pits at the N, near-silos at the W, and non silos at the E may indicate preferred placement of each type.

On sites where the density of pitting is high, there is often difficulty in discerning any trend in distribution of different sizes of pit, as for instance at Wyndyke Furlong, Oxon. (Muir and Roberts 1999). Again, at Gravelly Guy (Oxon.), with its very dense pit-field, the main cluster of pits contained a mix of small and large, whilst beyond this there were few large pits. This led to the only general conclusion, that the larger the pit the less likely for it to lie outside the main concentration (Lambrick and Allen 2004).

At Conderton Camp the few silo-pits found by excavation are of a size, general shape, and location similar to those noted at other sites (Thomas 2005). Unfortunately the absence of higher resolution magnetic mapping over unexcavated areas does not allow other candidates to be suggested (Marshall 1999). Here, two limestone slat-lined pits may well form a composite silo with a smaller lower compartment (FIG 25), rather than being vertically intersecting, as suggested in the original report (Thomas 2005: pits BB and CC in plate 37/p.76 and fig. 27/ p.73). The berm around the basal pit, broader toward the adjacent circular hut 3 (Thomas 2005: plate 36/p.75, and fig. 25/p.70) (FIG 25), may reflect a preferred line of entry, similar to that suggested for the stepped pits at The Park (Marshall 2007). Such structures, with few parallels elsewhere may well reflect restricted local practices, also suggested by the fairly extensive evidence for timber lining of pits at Conderton Camp, rare on most other such sites. Another potential silo, similar in diameter and slat lining to the suggested composite silo lies next to it, as does a near silo (pit II). Smaller non silo-pits within this cluster suggest paired usage as discussed at other sites where attenuated distributions allow a clearer pattern to emerge (FIGS 21-25).

Although the same general difficulties for interpretation remain, the situation becomes somewhat easier where simpler areas of pit accumulation, at lower final densities, can be identified, especially where there might be some structural impetus for establishment of a temporal sequence, as around a hut site. Two examples of such 'attenuated pit clusters' at The Park serve to illustrate such locations (FIG 21). A circular hut (hut 2), in an annexe abutting the main habitation sub-enclosure, was surrounded by a ring of pits, which may have been established in circular succession. This ring could represent a self-contained sub-sample of all types of pits in current use at the site, in their approximate proportions and spatial relationships. Here, numbers of non silo-pits appear to lie in small clusters around near silo-pits, with one or two pairings perhaps evident. A second circular hut (hut 1), at the margin of the main habitation sub-enclosure in which most of the pits were located, had its own cluster of pits ranged around it, not as clearly circular as for hut 2 in the annexe, but still appearing to be a localised sub-group related to the hut. Again the pattern is similar, but here with the non silo-pits lying towards the foreground of the hut and the larger near silo-pits ranged behind it. Several of the near silo-pits here have steps, which generally face the hut, suggesting a convenient direction of entry and inferring the existence of a cover.

Magnetic anomalies, of a type suggesting underlying storage-type pits, which occur packed within the main habitation enclosure at Conderton Camp (FIG 25), can be graded approximately by size to indicate the range present and gauge distributions. Such preliminary analysis, no substitute for data from excavation, is best done on the basis of high-resolution magnetic gradiometry (Marshall 1999), but the scan provided (Thomas 2005, fig. 4) does allow a preliminary assessment. There is one main, densely packed pit group, placed clearly as a dedicated area apart from the main huts, and five smaller clusters which occur elsewhere around the main habitation enclosure which also display a closer association with known huts. The main pit group indicates well-developed spatial organisation and fairly clear differentiation of pit-size, features seen weakly in the minor clusters.

At The Bowsings, the small pit-group in the interior angle at the front of the enclosure is set at some distance from the small habitation area, and again associations between non silo- and near silo-pits can be seen (FIG 22). At this site, the single large silo-pit is isolated in the opposite corner of the enclosure, without associated pits. Other attenuated distributions of pits, forming self-contained groupings suitable for spatial analysis, occur around huts elsewhere in southern Britain, producing similar conclusions to that suggested at The Park-Bowsings (FIGS 21-22). At Tollard Royal (Wilts.) for example, 34 pits and four 4-6 post structures lie around a circular hut, all within an

Linearites are very evident amongst pits, mainly running roughly transversely across the interior rather than being longitudinal, with row-elements of

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experimental Iron Age grain storage such patterns. Relative grading of the magnetic pit-type anomalies at Conderton Camp into larger, medium, and smaller gives the ratio 1: 3: 15, with the ratio of larger-medium to smaller being 1: 3.7. This might be in further broad agreement with the notion of the seasonal batch of pits comprising few larger unsealed or briefly sealed and refurbishable pits of longer lifespan intended for food grain, supplemented by a small cluster of lesser longer-sealed and more frequently replaced pits for seed-corn. The ratio of about 1:4 corresponds with that suggested during discussion of the model for grain storage, and by analysis of other sites, as above and in TABLE 22.

4-6 pits appearing amongst longer lines. A systematic use of space is clear, with progressive use and abandonment of pits, and pit-lines gradually filling the available space. Larger pits tend to appear more frequently towards the margins of this main group, with smaller pits occupying much of the interior. Such handy placement of larger pits, perhaps of covered rather than sealed type and allowing repeated access to food-grain, would make spatial sense, with smaller more-readily sealed pits, perhaps more for seed-grain, tending to be placed out of the way until opened and emptied. Placement of pits in lines would also simplify serial broaching of larger sealed pits, grain-filled in linear batches, and ease the onward movement of a covering superstructure placed to shelter each in turn during access. More piecemeal construction, use, and abandonment of single pits may also contribute to

Numbers of pits in each size-category for the sites discussed are given in TABLE 22.

TABLE 22: Distributions of pits within clusters excavated around huts. SITE The Park hut 1 hut 2 The Bowsings Tollard Royal Conderton Camp totals OVERALL RATIO percentage

PITS IN EACH SIZE CATEGORY [large ..to.. small] silo near silo non silo

all

1 0 1 3 1

4 6 5 11 3

7 12 8 20 33

12 18 14 34 37

6 1 5

29 5 25

80 13 70

115 100

Note: not all of the smallest pits, as noted at Tollard Royal, may be of potential grain-storage type, but discounting these does not affect the general conclusion.

different species (Wainwright 1968, 116). -remedial analysis of eroded pit groups Comparison of relationships between depth and diameter of pits at eroded and uneroded sites suggests a basis for assessment of truncation and repair of data sets, as at Manor Farm, Guiting Power where erosion has been estimated at 40cm (FIGS 16, 23; TABLE 23). As well as being apparent in comparative plots of depth versus diameter, the difference is also clearly visible in general data on pit volumes from both sites. Since the sites are broadly similar, it is unlikely that differences in agricultural practices existed to contribute to variation in general pit size, the main cause of differing surviving depth being erosion.

This sample suggests that silo-pits are relatively rare (5%), with near silos more common at 25%, and non silo-pits predominant at almost triple this (70%). These values suggest that a small kin group, as represented by one or two hut-sites, maintained one, or a few larger granary silos, with medium-sized and small pits being required in the ratio of about 1:2-3. Some division of the cereal crop between food-grain in larger pits, and seed-corn in smaller pits is possible, perhaps with duplication of the latter for added security. Alternative division of the grain harvest has been suggested elsewhere, as for instance at Tollard Royal (Wilts.), with food-grain placed in pits and seed-corn in above-ground granaries, noting some advantages to this for

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experimental Iron Age grain storage TABLE 23: Volumes of pits at The Bowsings (relatively uneroded) and Manor Farm (eroded). Site Park-Bowsings Manor Farm

excavated pits 58 52

surviving mean volume 1.77 1.25

s.d. 1.39 1.28

(m3)

1984). Pits with varying degrees of openness are found, but those of basically cylindrical form predominate.

If this estimate of erosion is added back to the surviving depths of pits at Manor Farm, then they can be reclassified in terms of volume into broad groups (non silo, near silo, and silo), and their spatial interrelationships examined in more detail.

Besides such descriptions of shape, the form of a pit can also be indicated in a more functional way, in terms of its degree of openness or constriction (TABLE 3). This can be further quantified by use of such statistics as ratio of depth to diameter (D), and related calculation of its potential to ventilate (V), and relative exposure of contents to dampness (E) (see the section 'Basic statistics used for analysis of pit groups').

Remedial analysis at Manor Farm suggests the following: ..existence of a small-scale arable economy The overall grain storage capacity of the site appears to have been small and consistent with its status as a farmstead which was localised in scope and near the base of the rural economy. In gross terms this is shown by the 52 pits excavated, a large proportion of the total sample visible at the site, having a modest cumulative storage capacity of about 50m3, or 28 tonnes, given a nominal conversion factor of 0.55 tonnes of grain per cubic metre of pit-storage. More detailed analysis of possible grain storage practices at the annual level, discussed in the general model outlined in this paper, also reinforce these general economic conclusions, which are very similar to those tabulated there for The Park-Bowsings.

The relatively shallow, open shape of many pits seems better suited for ventilation of contents than for effective deeper containment of stored loads under sealed conditions (FIGS 18-20). Any pit would be inherently more effective in storing a sealed load if its opening to the atmosphere was kept as small as possible relative to internal volume. Since most of the observed pit-shapes are basically cylindrical, storage of larger volumes could be simply achieved by digging deeper pits for any particular diameter, but this is not observed in the archaeological record.

..possible groupings of larger and smaller pits (FIG 23) The general ratio between larger near silos to non silos is about 1:2-3, suggesting the possible splitting of harvested grain into a larger bulk of possibly accessible food-grain, with several accompanying smaller deposits of seed-grain, perhaps sealed and more scattered for security. There are fairly discrete groupings of near silos, as seen at other similar sites. Linear arrangements of pits further suggest functional groupings and sequential use. ..the possible erasure of post-structures It is difficult to bring rectilinear post-built structures into the discussion as candidate above-ground granaries, given the possible diversity of their use (Cunliffe and Poole 1991) and the removal of all but larger post-holes at many eroded sites. One such robust post structure did, however, survive at Manor Farm.

Analysis of many pit groups indicates that the tendency was to construct relatively shallow pits, with depths somewhat less than diameter (D 5m3), 'silos' housing grain in transit, storing bulk grain on current deposit for consumption and trade, or receiving any incoming stocks from broached sealed pits; 'single mode' since remaining unsealed and fully accessible through weatherproof, roofed covers; their presence on a site may be status-related. The average lifespan of these types is likely to have decreased from the large silo, relatively stable because labour intensive to construct, to the more ephemeral small pit, replaced fairly rapidly if

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experimental Iron Age grain storage considered risky for contact with critical stocks of seed-corn, and perhaps refurbished by cutting back to provide a series of larger fresh pits, thereby progressing towards near silo type.

M.U. 1993. Excavations at Roughground Farm, Lechlade, Gloucestershire: a prehistoric and Roman landscape. Thames Valley landscapes: the Cotswold Water Park, volume 1.

The batch of pits required to store the harvest at a small farmstead of Park-Bowsings type, representing the basic unit of Iron Age agriculture, might have included one silo, one or two near silos, and a few non silos. Larger sites might have maintained this approximate ratio, but with increased numbers of each type in use, and perhaps a larger mean size for each.

Allen T.G., and Robinson, M.A. 1993. The prehistoric landscape and Iron Age enclosed settlement at Mingies Ditch, Hardwick-with-Yelford, Oxon. Thames Valley landscapes: The Windrush valley, volume 2. Oxford: Oxford Archaeological Unit/ Oxford University Committee for Archaeology. Andrews, A., and Jensen, T. 2005. Storing, handling and drying grain: a management guide for farms. Department of Primary Industries and Fisheries, Queensland, Australia. www2.dpi.qld.gov.au/fieldcrops/14983.html

-above-ground granaries: purpose-built structures possibly existing amongst small hypothetical rectilinear buildings supported on 4- and 6-post structures, but in the absence of clear identification and structural data impossible to assess as part of an overall system of grain production.

Araus, J.L., Slafer, G.A., Buxo, R., and Romagosa, I. 2003. Productivity in prehistoric agriculture: a physiological model for the quantification of cereal yields as an alternative to traditional approaches. Journal of Archaeological Science 30(6), 681-693.

-hut-based: likely to be a smaller-scale holding facility for more immediate use than for longer term bulk storage.

Bartali, El Houssine. 1987. Underground storage pits in Morocco. Tunnelling and underground space technology 2, 381-383.

The need for practical compromise Pit-based storage of grain arose from the combined need to cope with the consequences of increased productivity, to insure against an increasing external threat to stocks, and to cope with deteriorating weather conditions in the immediate post-harvest winter and spring. Sealing and concealment of strategic reserves was adopted for such purposes of security, despite this being less effective than maintenance of ventilated stocks, and was a necessary expedient rather than the preferred option. Where possible, the length of sealing was minimised, with pits being broached, covered, contents actively monitored, managed, and used as required.

Bateman, C., Enright, D., and Oakey, N. 2003. Prehistoric and Anglo-Saxon settlements to the rear of Sherborne House, Lechlade: excavations in 1997. Transactions of the Bristol and Gloucestershire Archaeological Society 121, 23-96. Bersu, G. 1940. Excavations at Little Woodbury, Wilts. Part 1: the settlement revealed by excavation. Proceedings of the Prehistoric Society 6, 30-111. Blaine, M.R. 1979. The Ioway Indians. Norman, Oklahoma: University of Oklahoma Press.

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Marshall, A.J. 2007. Farmstead and stronghold: development of an Iron Age and Roman settlement complex at The Park-Bowsings, near Guiting Power, Glos. (UK). Cheltenham: Guiting Manor Amenity Trust. ISSN 0960-197X.

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ACKNOWLEDGEMENTS The research forming this paper was sponsored by Mr E.R. Cochrane and the Guiting Manor Amenity Trust (Guiting Power, Glos., UK): their support is gratefully acknowledged.

Shepherd, I.A.G., and Shepherd, A.N. 1989. A grain storage pit of the pre-improvement period at Inchkeil, Duffus, Moray. Proceedings of the Society of Antiquaries of Scotland 119, 345-351. Stanford, S.C. 1970. Credenhill Herefordshire: an Iron Age hillfort

Equipment for monitoring conditions within pits was loaned by the Environmental Division, Coal Research Establishment (GL52 4RZ, UK), who also

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larger 'near silo-pit' (pit 5) at The Park/ environmental conditions within and outside the pit during the experiment.

Longer-term rainfall records for the area were made available by Norman Grisdale, at Meteorological Office Station 252858 (Guiting Power, Glos., UK).

FIGURE 9 GRAIN STORAGE EXPERIMENT 3: larger 'silo-pit' (pit 4) at The Bowsings/ the pit and the added covering structure shown in section.

CAPTIONS FOR FIGURES COPYRIGHT The author, A.J. Marshall produced all of the figures and plates and is the copyright holder, unless otherwise stated. Where material from other sources has been used as a basis for figures this is acknowledged (after: [author, publication]).

FIGURE 10 PROPERTIES OF PITS: Iron Age pits from The Park-Bowsings (Glos.): the range of their volumes, and of the ratio D between depth and diameter. FIGURE 11 PROPERTIES OF PITS: comparative data on pits from other Iron Age sites: the range of their volumes.

FIGURE 1 EXPERIMENTAL GRAIN STORAGE: location of the experiments in the Gloucestershire Cotswolds (the Guiting Power area).

FIGURE 12 PROPERTIES OF PITS: the range of pit profiles at The Park-Bowsings (Glos.).

FIGURE 2 EXPERIMENTAL GRAIN STORAGE: location of pits used for the experiments at The Park-Bowsings Iron Age enclosures (Guiting Power, Glos., UK). Plans of the sites are as shown by magnetic gradiometry. Data: raw, greyscale with black high.

FIGURE 13 PROPERTIES OF PITS: the range of pit profiles at Little Woodbury (Wilts.) (after Bersu 1940), and Gussage All Saints (Dorset) (after Wainright 1976). FIGURE 14 PROPERTIES OF PITS: the range of pit profiles A: at Danebury (Hants.) (after Cunliffe 1984; Cunliffe and Poole 1991); B: classification of pit profiles (after: Bersu 1940).

FIGURE 3 EXPERIMENTAL GRAIN STORAGE: rainfall in the locality of the grain storage experiments (Guiting Power, Glos., UK: SP 0924) Data for Guiting Power as recorded 1974-1996 (after: Grisdale, see Acknowledgements).

FIGURE 15 PROPERTIES OF PITS: Iron Age pits with highly constricted openings: archaeological and ethnographic examples. A: pits with conical profiles: Danebury (after: Cunliffe and Poole 1991; North America (after: Wilson 1987); Nigeria (after: Gronenborn 1997). B: the range of diameters for a cumulative sample of pits from Iron Age sites in southern England.

Rainfall zones: southern Britain Location of the three experimental sites mentioned in the text within the 75-100cm per annum rainfall band (after: The Library Atlas. 1981. London: George Philip. ISBN 0 540 053872). FIGURE 4 GRAIN STORAGE EXPERIMENT 1: smaller cylindrical pits (pits 1-3) at The Bowsings/ sections through the pits showing the location of instrumentation.

FIGURE 16 ANALYSIS: Iron Age pits from the Guiting Power area: samples from The Park-Bowsings (uneroded) and Manor Farm (eroded)/ the relationship between surviving depth and diameter, and an estimation of the degree of truncation. A linear regression line of depth on diameter, that is, estimating depth for a given diameter, is shown for the uneroded data.

FIGURE 5 GRAIN STORAGE EXPERIMENT 1: smaller cylindrical pits (pits 1-3) at The Bowsings/ environmental conditions outside the pits during the experiment. FIGURE 6 GRAIN STORAGE EXPERIMENT 1: smaller cylindrical pits (pits 1-3) at The Bowsings/ conditions within the pits during the experiment.

FIGURE 17 ANALYSIS: comparative data on pits from other Iron Age sites: regression lines relating depth to diameter. The regression lines given are those for depth on diameter, that is, estimating depth for a given diameter.

FIGURE 7 GRAIN STORAGE EXPERIMENT 1: smaller cylindrical pits (pits 1-3) at The Bowsings/ mean moisture content of grain stored within the pits during the experiment. FIGURE 8

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venting factor V and exposure E, as calculated for generic cylindrical pits of increasing depth and diameter, with specific data from pits at The Park-Bowsings superimposed. A: venting factor V; B: exposure E.

PLATE 2 Grain storage experiment 2: the unsealed silo-pit under an elongate timber-framed cover. Instrumentation was placed in the silo-pit, which was then filled with grain and its opening covered by a loose lid of planks. The entire silo was then placed under an elongate timber-framed superstructure, which was thatched to provide full weather-proofing. The entrance was further protected by an overhang of the roof and was closed by additional planking. A: the frame, as partially thatched. Scales: 2m; B: general view after the storage period, with the thatch removed. Scale (horizontal): 1m; C: after the storage period: a detail of the pit area showing the good condition of grain, but with some sprouting around the margin where light levels were sufficient to allow this. Scale (horizontal): 1m.

FIGURE 19 ANALYSIS: Iron Age pits from The Park-Bowsings and Little Woodbury: how the ratio D between depth and diameter, and venting factor V, change with increasing volume. FIGURE 20 ANALYSIS: operational properties of cylindrical pits: how venting factor V varies as the ratio D between depth and diameter changes. FIGURE 21 ANALYSIS: spatial distribution of pits of different capacities at The Park (Glos.). FIGURE 22 ANALYSIS: spatial distribution of pits of different capacities at The Bowsings (Glos.).

PLATE 3 Grain storage experiment 2: the unsealed silo-pit under an elongate timber-framed cover. A: the upper surface of the silo-pit after the 6-month storage period, showing the grain to be in good condition but with some marginal sprouting. Grain sampling by auger is in progress and pipes for other grain sampling are visible. Scale: 50cm; B: the silo-pit after removal of grain, leaving a crust of damper grain adhering to pit walls and base, with sprouting visible along its upper margin. Scale: 50cm; C: a detail of the crust of damper grain adhering to the walls of the pit, with drier surface grain (about 1cm thick) at upper left and an underlying matte of moist decaying grain (about 4 cm thick) at lower left, this being in direct contact with the damp bedrock wall of the pit shown at the right. Scale: 10cm.

FIGURE 23 ANALYSIS: spatial distribution of pits of different capacities at Manor Farm, Guiting Power (Glos.). Classification and mapping after estimation of original depths for truncated internal and external pit groups (after: Saville 1979; Vallender 2005), using data from relatively uneroded pits at The Park-Bowsings. FIGURE 24 ANALYSIS: spatial distribution of pits of different capacities at Tollard Royal (Wilts.) (after: Wainright 1968). FIGURE 25 ANALYSIS: spatial distribution of pits of different capacities at Conderton Camp (Worcs.) (after: Thomas 2005). FIGURE 26 A BASIC MODEL FOR GRAIN PRODUCTION AND STORAGE

PLATE 4 Grain storage experiment 3: the unsealed silo-pit under a conical timber-framed cover. A: the silo-pit, seen here before filling with grain, placement of instrumentation, and covering with a loose lid of planks, lies under a conical, timber-framed superstructure with central supporting-post, remaining to be thatched to provide full weather-proofing. Scale: 2m; B: the silo-pit, as originally excavated, with limestone slabs lying at the centre of the base, possibly to support a central post. Scale (external): 1m; C: the slabs in the silo-pit re-stacked to retain the base of a central upright post. Scale: 50cm.

CAPTIONS FOR PLATES PLATE 1 Grain storage experiment 1: sealed pits 1 and 2. Pit 1 (unlined) is in the background, and pit 2 (straw-lined) is in the foreground. Stone edging has been added around the upper margin of the pits to provide additional definition of the experimental area before sealing and backfilling to the level of the existing turf-line. Instrument pods, which held thermocouples and gas sampling tubes within the body of the stored grain, are visible. A: pits before filling. Scale: 2m; B: pits after filling but before sealing. Scale: 2m;

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