Event/Activity EPM291 - Fort Cumberland, Geophysical Surveys May 2017 to May 2023

Historic England carried out Ground Penetrating Radar (GPR) and fluxgate magnetometer surveys at Fort Cumberland, Eastney, between May 2017 and May 2023. The surveys aimed to identify subsurface remains across the site, particularly any surviving archaeological remains and utilities, and were undertaken as part of a wider non-invasive study to inform ongoing heritage management at Fort Cumberland. A hand-held fluxgate gradiometer survey (1.2ha) was conducted over accessible areas of the Parade Ground and vehicle towed GPR survey (2.5ha), using a composite of previous instrument tests together with newly acquired data, covered the Parade Ground and accessible areas in the dry moat. Both surveys successfully identified anomalies relating to services and evidence of structural remains associated with the fort. Both the Ground Penetrating Radar (GPR) and magnetic techniques successfully identified anomalies throughout the accessible areas of the site. The magnetometer survey responded to strongly magnetised fired brick and ferrous material, presumably associated with post-medieval structures and more recent ferrous services. GPR also detected a range of services, together with evidence for structural remains associated with both original elements of the fort defences and more recent temporary buildings shown on contemporary aerial photography. In particular, the GPR survey revealed evidence for the survival of the outer edge of the original 1747 fort rampart and ditch, the majority of which was over built by the later defences. Services revealed by both techniques complement and enhance a recent utility survey and suggest the presence of some additional historic drainage conduits, cabling and pipe. This includes a large central drain or cistern found to the north of the parade ground fed from a network of radial conduits and possible water supply pipes from the capped well-head further to the south. Evidence for more ephemeral features shown on aerial photography from the 1940s has also been revealed, for example the rectilinear anomaly adjacent to the hospital building and a curious polygonal patterned response found to the south of the parade ground.