Site Event/Activity record EEM14547 - 2015: GPR,MS,RS - Challacombe Common



GSB Prospection Ltd


June 2015


This part of Exmoor is host to a number of prehistoric monuments including cairns, standing stones and barrows with a significant grouping of the latter known as the Chapman Barrows. At the eastern end of these is Longstone standing stone and, beyond that, the Longstone Barrow, the largest barrow within this study area. The survey used detailed magnetometer (fluxgate gradiometer), earth resistance, and ground penetrating radar (GPR). The first area investigated a rectilinear earthwork and denuded barrow. The rectilinear earthwork appears to have structural elements associated with it as well as magnetic responses which would imply occupation or, at least, some form of anthropogenic activity rather than this being a ‘sterile’ monument. Potentially associated with the earthwork are magnetic responses across a low platform to the northeast, which is possibly evidence of livestock management. The barrow has a central funerary feature and encircling ditch, both identified by the magnetic survey; the latter appears segmented but this may be a result of degradation of the monument. The second area was another denuded barrow, this also had an encircling ditch. It was difficult to ascertain whether there was a central funerary feature as one quarter of the monument produced very little response; whether this was purely a data-collection effect or evidence of previous unrecorded excavation remains uncertain. The resistance survey revealed no internal structure, an interpretation fully endorsed by the GPR survey which revealed almost nothing but natural responses. The final survey area over the Longstone Barrow produced the most striking results. The ditch produced a clear circular response in all three datasets; the magnetic data show that it is cut into non-magnetic subsoils or geology, producing a negative response. The resistance data show a marked change in response character above and below a ‘shoulder’ on the flanks of the mound, readily noticeable in the topographic data. It has been assumed that this shoulder indicates that the monument was constructed in two phases and the resistance data seem to confirm this. Had it been built in one phase the change is unlikely to have been so abrupt. Again geophysics has been shown to be a useful investigative research tool, despite the difficulties thrown up by both the Exmoor terrain and vegetation.

Sources/Archives (1)

  • <1> Report: Adcock, J.. 2015. Geophysical Survey Report G1515: Challacombe Common, Exmoor National Park.



Location Challacombe Common, Challacombe Parish, Devon
Grid reference Centred SS 6938 4305 (2754m by 650m) (Surveyed)
Map sheet SS64SE

Related Monuments/Buildings (3)

  • Chapman Barrows on the Parracombe/Challacombe Parish Boundary (Monument)
  • Longstone Barrow, Challacombe Common (Monument)
  • Rectangular earthwork and barrow on Challacombe Common (Monument)

Record last edited

Jun 1 2016 9:07AM