Gwernvale is a polygonal tomb chamber, which was excavated between 1977 and 1978 in advance of road works. The excavations revealed a long barrow with three chambers and a complex pre-tomb sequence that had included Meso-Paleo material.

Source: Briggs, C.S., 1997, An Inventory of the Ancient Monuments in Brecknock (Brycheiniog), The Prehistoric and Roman Monuments, Part i: Later Prehistoric Monuments and Unenclosed Settlements to 1000 A.D. RCAHMW. pp 56-60.

RCAHMW, February 2011