Case Study 3 - Culverwell Mesolithic site, Portland Bill, Dorset
Site summary
Culverwell is an important Mesolithic site near Portland Bill, Dorset, dating from about 7,500–8,500 BP. The site was discovered in 1966 after ploughing uncovered large quantities of mollusc shells.
A small team of volunteers began excavating in 1967 and continued over the years. After the final excavations in 1996, the majority of the site was backfilled, except for one area about 14 metres by 6 metres, which was left exposed in a timber shelter (see Figure 1) so that the public could see it.
The site was added to the Heritage at Risk Register in 2008 because the exposed part of the site was degrading. A decision was subsequently made to rebury it.
Reburial objectives
The site had been exposed for 40 years within a timber shelter, and the proposal was to permanently rebury it to protect it from erosion and burrowing animals.
Significance
Culverwell is a nationally important site, with evidence of hearths and knapping areas. It is one of a small number of Mesolithic sites with evidence of occupation. It is thought to have been a settlement for around 20 people at a time when the population of Britain is estimated to have been below 5,000.
Comprising a large shell midden (rubbish dump) and associated hearths, the site provides an insight into how Mesolithic people lived and used the resources around them.
Condition assessment
The site was left uncovered within a timber shelter to allow visitors to experience the archaeology at first hand. However, animal burrowing and increasingly stormy weather (which caused the shelter to degrade), damaged the exposed archaeological remains. The decision was made to rebury the site to preserve the artefacts, ecofacts and other forms of evidence within it.
Culverwell is a timely reminder that cover buildings only have a limited lifespan. When they are designed and built, consideration needs to be given to on-going monitoring and maintenance, as well as what will happen when they reach the end of their design life.
Risk assessment
Years of exposure within the cover shelter led to the archaeology becoming vulnerable, with rainwater run-off and animal burrowing adding to the decay. The idea of covering up the site so that it was no longer publicly accessible and the costs of reburial materials meant that the owner was initially resistant to reburying the site.
Support from Historic England, both financially and from our specialist teams, was critical in securing the long-term survival of the site.
Reburial design
Environmental criteria
The site was at risk from burrowing animals, drawn to the security of the cover shelter. It was felt that removing the structure and reburying the archaeological remains would stop the burrowing.
A balance was required between thermal protection (which could have been provided by a deeper depth of reburial material) and the need to avoid creating an artificial mound that may attract burrowing animals (by creating an artificial warren). Additionally, there are prehistoric earthwork features on Portland. It was, therefore, important that the reburial area was returned to ‘natural’ topography as far as possible, and that additional mounds were not introduced into the landscape.
Functional criteria
The reburial proposal returned the site to grassland to be grazed. This low maintenance solution requires little additional input now that the reburial material has stabilised and the grass is established. As the site is protected as a scheduled monument, there will be ongoing engagement with the owner over its future management, with low-level grazing being the preferred option.
Programmatic criteria
Having been exposed for the public to view for 40 years, the purpose was a complete, final, permanent reburial. No short- or medium-term options were required.
Summary
Prior to backfilling, scientists from the Historic England Fort Cumberland Laboratories, along with volunteers from the Association for Portland Archaeology (APA), cleaned and recorded the exposed sections and surfaces. Limited samples were taken to better understand the current condition of the site and inform the methods for its preservation. This ensured that the most suitable reburial methodology and materials were chosen.
Locally sourced archaeologically sterile soil was placed onto the exposed surface, deep enough to provide effective thermal cover without creating a mound (about 20-30cm). Once firmed in place, the soil was left to settle and locally sourced grass seed was sown.
Stakeholder consultation
Historic England provided advice to the owner and volunteers from the APA to support the removal the cover structure and to backfill the site to ensure its long-term protection. As the advisor for the Department for Culture, Media & Sport, Historic England provided comment on the Scheduled Monument Consent submitted in advance of the works.
Maintenance and monitoring
To encourage the newly seeded backfilled area to establish, grazing was not introduced in the first year. Now that the ground has settled and the grass is established, a low-level grazing regime has been introduced as the most suitable way to manage the site.
Documentation
In 2019, Historic England carried out a 3D digital photogrammetric survey of the site to allow virtual access.
Details of the reburial design were submitted to Historic England as part of the Scheduled Monument Consent for the work and they are held on file.
Archive material associated with the backfilling is held at Fort Cumberland Laboratories. The site excavation report documents the location of the archive, including previous reports and artefacts.
