Aerial photograph showing the excavation of the Neolithic causeway.
Part of the Neolithic causewayed enclosure during excavation © OCA jv 2015
Part of the Neolithic causewayed enclosure during excavation © OCA jv 2015

Assessing the Impact of Proposed Development: a Case Study from Thame, Oxfordshire

By Richard Oram, Lead Archaeologist, Oxfordshire County Council and Gerry Waite, Director, Triskelion Heritage​

Archaeological assessment and evaluation – finding out what’s on the development site

When land to the north west of Thame was allocated in the South Oxfordshire Local Development Framework (LDF) there was very little evidence to suggest that significant archaeological features survived on the site. It lay outside the medieval settlement of Thame and the only Historic Environment Record (HER) entry for the site was a reference to a ‘Belgic’ jar recorded as ‘dug up by a badger’ and reported in Oxoniensia in 1966. Very little archaeological investigation had been undertaken in the area although a series of Neolithic pits, a Bronze Age barrow and Iron Age pit alignment were being excavated 1.2 kilometres to the north-east.

The very limited evidence made it difficult to give specific archaeological advice on this site within the LDF. This was not an unusual situation since many areas within the County have had very little archaeological investigation, hence the lack of information in the HER. We therefore highlighted in the LDF that a desk-based assessment would be required to assess the archaeological potential of the site should a planning application be submitted in the future.

An archaeological desk-based assessment undertaken in 2010 found little evidence and concluded that there was low to moderate potential for archaeological remains to be present on the site. It also suggested that the absence of archaeological evidence may simply have resulted from the lack of previous investigation, drawing attention to other important sites in the vicinity. When 21 geotechnical test pits were archaeologically monitored in 2011 the results seemed to confirm the results of the assessment since archaeological features were observed in only two of the test pits.

By the time a planning application was submitted in 2014 the HER had acquired new Lidar data that enabled the topographical location of the site on a plateau, an area of high ground overlooking the confluence of two rivers, to be modelled in 3D and compared with the similar position of the prehistoric site to the north-east. This suggested that the development site would also have been attractive for prehistoric settlement. As a result it was clear that an archaeological evaluation would be needed to find out whether archaeological deposits survived on the site and to assess their significance, before a decision could be taken on the planning application.

During evaluation in the autumn of 2014 the higher areas of the site produced an abundance of archaeological remains dating from the Mesolithic through to the post-medieval periods. The main focus of activity was located on the plateau and comprised later Iron Age and Roman features including numerous pits, ditches and human burials.

Archaeological excavation in advance of development – the results

The evaluation had demonstrated that the site contained considerably more archaeological interest than previously assessed. Since this type of site was not particularly unusual for the County and nothing was found to suggest that the site was of such significance as to prevent development, planning permission was granted but with conditions attached to the permission requiring archaeological excavation before development.

The project was undertaken jointly by Oxford Archaeology and Cotswold Archaeology. The initial phase of the excavation recorded an Iron Age enclosure and settlement evidence as expected from the evaluation results. On the plateau area new and important features not suggested by the evaluation were however encountered. Eleven early-to-middle Saxon sunken featured buildings were found along with a possible hall building.

By far the most significant discovery, however, was part of a triple-ditched early Neolithic (about 3800 BC) causewayed enclosure, a monument of national importance. A number of early Neolithic pit clusters also highlighted the importance of this location just prior to, or contemporary with, the causewayed enclosure. A hengiform monument and a probable barrow ring-ditch were also recorded within the enclosure.

The causewayed enclosure was mainly overlain by the later Iron Age and Roman features and the subtle differences between the fills of the enclosure ditch and the surrounding natural deposits made it very difficult to identify. During the evaluation the areas investigated were ones where the causewayed enclosure ditch had already been cut away by the later features, explaining why this important monument was not identified during evaluation.

Subsequent evaluation and geophysical survey of a wider area as part of later phases of development have identified and located almost the complete circuit of the causewayed enclosure, enabling a larger part of it to be preserved. The excavations undertaken on its north-eastern quarter have provided an abundance of evidence and artefacts, which can be studied and may help to understand these enigmatic monuments.

Outcomes – the importance of evaluation

This nationally important monument, which can now be protected and preserved from future damage, was completely unknown when the initial site allocations were made. The case demonstrates that significant archaeological sites still remain to be discovered in Oxfordshire.

The implementation of national planning policies covering the assessment of the significance of heritage assets prior to development through archaeological assessment and evaluation ensures that such sites are discovered early in the planning process. When this is done, provision can be made for their protection and/or investigation as appropriate. Despite the lack of information on the HER for the Thame site, its potential was demonstrated through the staged process of assessment and evaluation. Without such evaluation in advance of development, nationally significant sites such as this would not have been recorded or protected.

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