4.14 The Ancient Monuments Laboratory
Archaeometry
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Geophysics
Some 30 sites have been surveyed during the year, and in addition to the spectacular results from Stanton Drew (described separately below), there are other excellent geophysical surveys to report. The coverage of Wroxeter, a joint exercise with Geophysical Surveys of Bradford, has been completed, revealing for the first time an entire Roman city in a magnetic image composed of some three million data points. The wealth of new information is staggering. In comparable detail, but on a smaller scale, survey of the environs of Catterick in Yorkshire has imaged the lay-out of the two Roman forts; many new features have been revealed and enable the assessment and publication of recent excavations to be placed in a much more coherent context than could otherwise have been possible. Other surveys have included Roman villas and industrial sites, medieval priories, castles, and a Tudor palace. At Lelissick in Cornwall, a multitude of ring ditches and other features, probably representing a pre-Roman
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settlement complex, has been planned in detail for the first time. Two long barrows, at Tilshead on Salisbury Plain and at Shepherds Shore near Avebury, have been shown to retain substantial internal structural components. A findspot of Viking hack silver in Lancashire has been investigated, using magnetometry, resistivity profiling, and ground penetrating radar. The fieldwork phase of the Wessex Hillforts Survey Project has been completed, with comprehensive coverage of 20 hillforts. The quality and range of results from apparently barren hillfort interiors, such as at Castle Ditches, Wiltshire, continues emphatically to press home the value of this approach to the future academic understanding and conservation of such monuments. The results of the surveys are now being collated and analysed for publication.
Most successful public demonstrations of geophysical instruments and methods were held at Clun Castle, Shropshire, for Science and Engineering Technology Week 1998. The Branch also organised, on behalf of the Environmental and Industrial Geophysics Group, a well attended and stimulating day meeting at the Geological Society, Burlington House, devoted to Recent work in archaeological geophysics. The English Heritage Geophysical Survey Database (WWW: http://www.eng-h.gov.uk) continues to make progress, now holding information on over 1400 survey visits, including an increasing percentage of those undertaken by commercial and other surveyors. Collaboration with the Archaeology Data Service is aiming at avoiding duplication and will ensure that future UK geophysical survey data are archived to appropriate standards.
Stanton Drew, Somerset
Despite an increasingly refined methodology, geophysical survey is still rarely capable of directly detecting the traces of timber structures. A remarkable exception to this generalisation was achieved in September, 1997, when detailed magnetometer survey located the faint traces of hundreds of post-pits within the megalithic Great Circle at Stanton Drew, near Bristol. The arrangement of these pits into a pattern of concentric circles implies the former presence of an immense structure, at 95m across the largest of its kind yet discovered. The survey also demonstrated that this structure, and the stone settings, are themselves encircled by a previously unsuspected henge ditch.
The stone circles, avenues, cove, and outliers at Stanton Drew were first
recorded by John Aubrey in 1664. Although comparable to the intensely studied
monument complex at Avebury, c
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The fluxgate survey revealed nine concentric rings of anomalies within the Great Circle. The outer ring has a diameter of 95m, the inner one is c 18m across, and at their centre is a cluster of other anomalies suggesting pits. The lack of response from the southern part of the circles is probably owing to the presence of a former field boundary. The entire complex, including the stone circle, is surrounded by a 7m wide ditch with a broad 50m wide gap to the north-east. At the centre of the smaller stone circle four anomalies were detected, seemingly aligned with the four opposed pairs of stones that comprise the circle. These anomalies might be hearths, pits, or former stone settings. A pair of faint linear anomalies leading north-eastwards to the perimeter of the circle possibly represents an inward extension of the outward stone 'avenue' on the same alignment.
A more detailed survey was carried out using a caesium magnetometer to try to obtain a more refined image of the rings within the Great Circle. Use of a very sensitive instrument (a Scintrex Smartmag) coupled with a narrower sampling interval, has clarified the definition of the anomalies. Individual pits are most clearly identifiable in the outermost ring where they seem to be approximately 1m wide and spaced at similar intervals. Elsewhere the rings are less identifiable as individual anomalies than by the overall geometric pattern. Apart from the ring pattern there is a hint of internal structuring in the form of a corridor or aisle leading from the centre of the site.
Individually distinct anomalies within the rings can be interpreted with confidence as pits, although the presumption that these once held timbers (on analogy with excavated sites), cannot yet be confirmed. The magnetic enhancement responsible for the anomalies might have been caused by the burning of timbers in situ or, more speculatively, by the development and concentration of magnetite introduced by microbial activity in the organic-rich residue of the former timbers. The soil, developed over Keuper Marl, is sandy and unconsolidated to a depth of some 2m and would have been well suited to the emplacement of timber uprights. The anomalies at the centre of the Great Circle are less certainly prehistoric in origin as there is ferrous disturbance present that might result from unrecorded antiquarian digging. The possibility still remains, however, that some contemporary central feature or features might survive.
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The results of geophysical survey considerably enhance the status of Stanton Drew among Neolithic Bronze Age ceremonial sites in the British Isles, not only as one of a small number of circle henges, but as an example that also includes a timber construction of unprecedented proportions. This feature has parallels with several other sites, both far afield as at Balfarg, Fife and more locally within Wessex, at Durrington Walls, Mount Pleasant, Woodhenge, The Sanctuary and, not least, at Stonehenge itself, and the results emphasise yet again the radical impact that non-intrusive geophysical technologies can have on transforming archaeological knowledge. There still remains considerable potential for more extensive and detailed geophysical investigation at Stanton Drew using a range of methodologies. In conjunction with full measured and topographic survey, these will aim to refine the patterns within the Great Circle, and their interrelationships, and extend the survey to cover the outlying south-western stone circle. In the meantime a conservation plan for the site is being drawn up by the Stanton Drew Steering Committee, which comprises representatives from the local authority (Bath and NE Somerset), the University of Bristol, the Avon Archaeological Unit, and English Heritage.
Radiocarbon dating
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This year work has continued with collaborating radiocarbon laboratories, who have processed 211 samples from 31 sites. Projects such as dating the Bronze Age plank-sewn boat from Dover and the seventh-century Anglo-Saxon cemetery at Buttermarket, Ipswich require particularly high-precision measurement. To enable us to use this sort of analysis for commissioned archaeological projects wherever appropriate and to undertake new research into particularly problematic areas of archaeological chronology, we have provided a grant to enable the Queen's University, Belfast to expand their facility.
Extensive dating programmes for the major complexes of prehistoric monuments at Hambledon Hill, Dorset, and Raunds, Northamptonshire are nearing completion. Although it is a more conventional site, Yarnton, Oxfordshire, has provided the most spectacular results for the year. A piece of carbonised bread has been dated to cal BC 3620-3350 (4673 samples funded by English Heritage 1997-98)
Dendrochronology
Once again tree-ring analysis of over 50 standing buildings has been commissioned during the year. The majority of cases are those where there is a need to inform the course of repair programmes for which English Heritage provides grant aid, although a significant number of buildings that appear on the Buildings at Risk register have also been analysed as part of our proactive approach to these difficult cases. Three cathedrals have also seen major programmes of tree-ring analysis this year. The final report on a fifteen-year campaign to date the roofs of Lincoln is nearing completion and demonstrates the potential of dendrochronology, integrated with extensive recording of fabric and documentary research, to unravel the sequence of such complex structures.
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In contrast, analysis of the surviving medieval timbers from the nave of Peterborough cathedral has begun this year. Nearly 70 joists that support the painted ceiling have been shown to be part of the original fabric, although work on the boards of the ceiling itself has only just started. At Salisbury work is also progressing on the roofs of the eastern chapels. These are thought to be largely original, but are currently the subject of major repairs, which will require the replacement of some timbers.
The first phase of a research project to construct prehistoric tree-ring chronologies for southern Britain is also nearing completion, with dated chronologies produced for Wootton-Quarr, Isle of Wight, the Somerset Levels, and the Severn estuary, and a floating sequence for Shinewater, Eastbourne. Although this project has improved the coverage and replication of chronologies for the prehistoric period, these are still patchy and weak.
Archaeometry
Environmental Studies
Technology
Conservation