Tuesday, January 3, 2012

Review: Gathering Time: Dating the Early Neolithic Enclosures of southern Britain and Ireland

Alasdair Whittle, Frances Healy, & Alex Bayliss. Oxbow books, Oxford, 2011. 2 Volumes, xxxviii+992pp. ISBN 978-1-84217-425-8. £45 (via Oxbow) or £50.07 (via Amazon).

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For anyone with an interest in Irish and British prehistory and, specifically how the chronologies are assembled through radiocarbon dating, the publication of Gathering Time: Dating the Early Neolithic Enclosures of southern Britain and Ireland has been long anticipated and much, much desired. It is hard to overstate the importance of this book and how it has already rewritten our understanding of Neolithic enclosures, but it also stands as a template for other intensive studies to follow and emulate. The central importance of this study is not simply that it uses a lot of new radiocarbon dates for various sites, but it is how this data is treated and processed on such a large scale that is already leading to new and exciting insights into prehistory. As many readers of this blog, both professional archaeologists and enthusiasts, will be aware, the advance of absolute chronologies in archaeology has, in large part, been due to the development of radiocarbon dating. Prior to the seminal work carried out by Willard Libby and his team (James Arnold and Ernie Anderson), archaeological sites and were only datable through relative chronological means, such as seriation etc. In 1960 Libby, Arnold and Anderson won the Nobel Prize in chemistry for their work on radiocarbon dating. The basis of the method was that the measurement of the amount of the radioactive isotope carbon 14 (14C) surviving in a sample could be utilised to determine when, say, a piece of wood had been cut or grain harvested. These early dates relied on the assumption that the amount of 14C in the atmosphere had remained constant throughout history and, as the discipline was in its infancy, the associated standard deviations were also quite large. Over the years parallel advances in calibration of dates against tree ring curves, more sophisticated methods and machinery, along with increased care and refinement in the selection of materials and samples has led to better results. Today radiocarbon determinations have better accuracy and precision than ever before. Nonetheless, even with careful sample selection and the use of high-quality AMS dating, there is still the possibility that, when calibrated, the date will range over several decades to centuries. Since the 1990s a number of researchers have explored and developed a statistical system known as Bayesian modelling. The approach derives from the ideas of Thomas Bayes, an 18th century Presbyterian minister and mathematician. Simply put, this method allows the calculation of how the degree of belief in a given proposition changes due to additional evidence. In archaeological terms, the application of Bayesian modelling allows the refinement of radiocarbon dates through the addition of contextual information. Such information may include multiple dates for individual deposits, stratigraphic relationships, or even closely datable artefacts such as coins or pottery. To take an example from my own experience: at Gransha, Co Londonderry, I excavated a small pit group. A radiocarbon date from charcoal recovered from one of the features indicated that it had been deposited in the Early Neolithic period (4930±70 BP), but the date range was some 405 calibrated years (3943-3538 cal BC). As part of the INSTAR Cultivating Societies project at QUB additional radiocarbon dates were commissioned and then modelled by Rick Schulting and Paula Reimer (Chapple 2008, Appendix 7). The end result was that the potential lifespan of the site was reduced from 405 years to 0-50 years – a vast improvement on the earlier result from a single radiocarbon date. [Introductions to Bayesian modelling may be found here and here].

What Gathering Time set out to do was exactly like the example above, but on an enormous scale. Not only was the aim to produce robust chronologies for individual sites, but to then place them in wider chronologies and within their geographic and typological settings. The book presents 871 radiocarbon dates from nearly 40 causewayed enclosures. To assess how causewayed enclosures functioned as part of the wider Neolithic landscape and society models were also prepared for a range of monument types, including long cairns and long barrows. This brings the total analysed radiocarbon dates to a startling 2350. As such it is the largest Bayesian modelling project ever undertaken. The central findings of the project are that the main period of causewayed enclosure construction lasted from the late 38th century cal BC to the mid-to-late 36th century cal BC. Although a number of sites had an active life of several centuries, many were used for relatively shorter periods – some for only a matter of decades. When this data is incorporated into wider models, encompassing the entirety of the evidence, it is shown that the causewayed enclosures only appeared three centuries after the first Neolithic practices were established in southern Britain. The process of ‘Neolithisation’ is shown to have begun in south-eastern England and spread regionally over two centuries.

Chapter 1, ‘Gathering time: causewayed enclosure and the early Neolithic of southern Britain and of Ireland’ (Whittle, Healy, & Bayliss) addresses questions of time and chronological resolution, along with a presentation of causewayed enclosures and the history of their research. Chapter 2, ‘Towards generational timescales: the quantitative interpretation of archaeological chronologies’ (Bayliss, van der Plicht, Bronk Ramsey, McCormac, Healy, & Whittle) provides an introduction to Bayesian modelling and the project methodology. In particular, it examines the necessary prerequisites for successful implementation of the Bayesian approach – from prior knowledge about sample data (taphonomy, association, stratigraphy etc.) to the tacit statistical assumptions involved in this form of model building.

For the purposes of this project, southern Britain has been divided into what the authors describe as ‘pragmatically defined regions’. Chapters 3-11, each deal with the enclosures of a southern British region and place them in the context of contemporary Neolithic activity. In each of these chapters models are presented, along with a review of the broader implications of the new chronologies. In Chapter 3, ‘The north Wiltshire Downs’ (Whittle, Bayliss, & Healy) Windmill Hill, Knap Hill, and Rybury are examined. Chapter 4, ‘South Wessex’ (Healy, Bayliss, Whittle, Allen, Mercer, Rawlings, Sharples, & Thomas) looks at Hambledon Hill, Whitesheet Hill, Maiden Castle, and Robin Hood’s Ball. Chapter 5, ‘Sussex’ (Healy, Bayliss, & Whittle) presents Whitehawk Camp, Offham Hill, Combe Hill, The Trundle, Bury Hill, Court Hill, Barkhale, and Halnaker Hill. Chapter 6, ‘Eastern England’ (Healy, Bayliss, Whittle, Prior, French, Allen, Evans, Edmonds, Meadows, & Hey) is divided into five sub regions: The Chilterns (Maiden Bower); The Great Ouse catchment (Great Wilbraham, & Haddenham); The Nene Valley (Briar Hill); The Lower Welland Valley (Etton, Etton Woodgate, & Northborough); and East of the Fens. Chapter 7, ‘The Greater Thames estuary’ (Bayliss, Allen, Healy, Whittle, Germany, Griffiths, Hamilton, Higham, Meadows, Shand, Stevens, & Wysocki) presents Lodge Farm, St. Osyth, Orsett, The Essex side of the Thames estuary, Kingsborough 1 and 2, Chalk Hill, The Kent side of the Thames estuary, and The Thames Estuary and Beyond. Chapter 8, ‘The Thames Valley’ (Healy, Whittle, Bayliss, Hey, Robertson-Mackay, Allen, & Ford) presents Yeoveney Lodge Farm, Staines, Eton Wick, Gatehampton Farm, Goring, and Abingdon. Chapter 9, ‘The Cotswolds’ (Dixon, Whittle, Bayliss, Hey, & Darvill) examines Crickley Hill and Peak Camp. Chapter 10, ‘The south-west peninsula’ (Whittle, Bayliss, Healy, Mercer, Jones, & Todd) presents examinations of Membury, Hembury, Raddon Hill, Helman Tor, and Carn Brea. Chapter 11 (in volume 2), ‘The Marches, south Wales and the Isle of Man’ (Bayliss, Whittle, Healy, Ray, Dorling, Lewis, Darvill, Wainwright, & Wysocki) looks at the sites of Hill Croft Field, Beach Court Farm, Ewenny, Banc Du, and Billown. Chapter 12 ‘Ireland’ (Cooney, Bayliss, Healy, Whittle, Danaher, Cagney, Mallory, Smith, Kador, & O’Sullivan) deals in the same way as each of the above regions, but with the island of Ireland as a whole. The examination of dates from the Donegore Hill and Magheraboy causewayed enclosures, along with a host of associated determinations, allows the authors to argue that the Neolithic in Ireland began around 3800 cal BC. The general conclusion of these chapters is that there is no precedent for the majority of the elements that define the Early Neolithic in the preceding Mesolithic. These innovations include the domestication of animals, cereal cultivation, rectangular timber structures, bowl pottery etc. The authors conclude that these elements of Neolithic life first appear in the Greater Thames estuary during the 41st century cal BC. From there the process of Neolithisation spreads slowly into southern and eastern England, then west into Wales and the Marches by 3700 cal BC. The early dates from domesticated cattle bones at Ferriter’s Cove, Co. Kerry, have been taken to suggest that Neolithic migrants had unsuccessfully attempted to colonise Ireland, ahead of the later Thames estuary venture. The remarkably early dates from the Magheraboy, Co. Sligo, enclosure (40th to 39th centuries cal BC) are difficult to accommodate within the available models. Not only are they significantly earlier than the English examples, but they predate the emergence of other Neolithic practices on the island from the late 39th to early 38th centuries cal BC. Based on the totality of the evidence, it is argued that the Neolithic way of life was first introduced to Britain and Ireland from the near Continent. Similarities in bone and cereal assemblages suggest a number of possible points of origin, including: Brittany, Normandy, Calais, the Paris Basin, Flanders, and the southern Netherlands. One of the models advanced suggests that numerous small-scale migrations occurred from multiple departure points, over the course of 200-300 years. Another proposes a near-simultaneous, large-scale emigration from the Continent, while a third is a combination of the two with a small number of pioneers, followed by larger numbers over time. While the authors examine all of these scenarios in detail, their preferred explanation is of a relatively small ‘founder pool’ of migrants crossing from the Calais region into the Thames estuary and south-eastern England. Rather than a large-scale influx of people, the authors argue for rapid acculturation of the native population, especially from the 39th century cal BC; though they do allow for further waves of Continental migrants coming across the English Channel.

Chapter 13, ‘Carbon and nitrogen stable isotope values of animals and humans from causewayed enclosures’ (Hamilton, & Hedges) was, essentially, a sub-project within the greater whole. The aims of this work were to document isotopic variation as thoroughly as possible; to measure the average range of human δ15N values from causewayed enclosures and compare them to the available data from chambered tombs; and to measure the differences in human and animal δ15N values. The authors conclude that results from the causewayed enclosures fit the emerging pattern for the whole of the Neolithic in southern Britain. Analysis of the animal remains indicated that the values for cattle, sheep, and pig differ consistently across all sites. In particular, pigs showed elevated δ13C values, which is interpreted as evidence for foddering in wildwood resources. Pigs also displayed slightly elevated δ15N values relative to cattle and sheep, but not of the order present in later assemblages. This is taken to suggest that a different management regime was in place during the Early Neolithic. Analysis of the human-faunal difference is interpreted as evidence for a high proportion of animal protein (either meat or dairy) in the diet. Chapter 14, ‘Neolithic narratives: British and Irish enclosures in their timescapes’ (Bayliss, Healy, Whittle, & Cooney) attempts to ‘weave narratives out of the chronological threads spun from the models constructed in the course of the regional discussions’. This is an extremely complex and involved chapter that, I am sure, will be the basis for discussion and debate for some time to come. The central conclusion of the chapter is that while ‘all models are wrong’ the intensive work on the Bayesian models and various alternative approaches, all showing similar results, may reassure us that the results are not ‘importantly wrong’. Even so, the authors make it explicit that the models presented here are not definitive, but are their preferred interpretations, based on the quality of the data available. Chapter 15, ‘Gathering time: the social dynamics of change’ (Whittle, Bayliss, & Healy) attempts to bring the evidence for the entire range of Early Neolithic life experiences together, moving beyond the enclosures to the transfer of artefacts and the husbandry and slaughter of livestock etc. In particular, the new chronological framework that the project has revealed allows a series of different timescales to be examined. These include the scales of generation, lifetime, active social memory, and longer-term structures like myth and story. Finally, the authors suggest that we are now at a point where the term ‘prehistory’ may be usefully abandoned. While terms such as ‘(pre)history’, and ‘protohistorie’ are rejected, alternative titles are proposed: ‘total history’, ‘absolute history’, and ‘total archaeology’. A final appendix, ‘Some unanswered research questions for southern British enclosures’ (Healy, Whittle, & Bayliss) give a succinct list of questions, the answers to which would greatly add to our understanding of the individual sites mentioned, and aid in further refining the author’s models.

The debate as to the function of causewayed enclosures has been around for some time and the authors examine the possibilities, from places of assembly to defuse tensions between rival groups keen to exploit the same limited resources, to places of political and dynastic ritual where access was granted only to a privileged few. However, no amount of dates and chronological refinements can elucidate the meanings that these sites had to their creators and those who witnessed and partook in the ceremonies carried out there. Nonetheless, analysis of the dates does suggest that they were constructed in three defined phases from an experimental start where a range of shapes and sizes of enclosures were attempted. This was followed by a rapid expansion of the numbers of enclosures being constructed, increasingly to a common template. Finally, small communities built their own enclosures to express their own independent identities. The authors admit that the precision with which we may now examine the commencement of the causewayed enclosure phenomenon is not replicated in how we understand their demise. They appear to have been abandoned, but not wholly forgotten. They frequently survived in the landscape, sometimes reused and with their ditches recut. As I said at the beginning, the importance of this work is not simply that it has forced a large-scale rewriting of the process of Neolithisation and presented us with a fine-grained chronology of the period, but that it now serves as a template for other researchers to follow. Whether they study other geographical areas or different time periods, Gathering Time now shows the way forward to us all.

Notes: 1) Robert M Chapple wishes to acknowledge the financial assistance provided under the Built Heritage element of the Environment Fund by the Department of Arts, Heritage and the Gaeltacht towards the Irish Radiocarbon & Dendrochronological Dates project [IR&DD Facebook Page].

2) I am indebted to Christopher Catling’s (2011) review of Gathering Time for helping me make sense of this vast amount of data.

References:

Chapple, R. M. 2008 ‘The excavation of Early Neolithic and Early Bronze Age sites at Oakgrove, Gransha, county LondonderryUlster Journal of Archaeology (3rd Series) 67, 22-59.

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