The ridge known as Cefn Drum, oriented south-west/north-east, is an area of common heathland of mostly low altitude (less than 230m) which extends north-east onto the steeper and more prominent Twyn Tyle. Extensive remains of early agricultural and settlement landscapes survive here, on its summit and south-facing slopes, mostly of medieval and later date but also with some evidence for prehistoric activity which becomes more prevalent further to the north-east.
Just below the highest point of Cefn Drum is a kidney-shaped hollow measuring 30m long (E-W) by 10m wide and no more than 0.5m deep. Although the hollow is now dry it may once have served as a dewpond in an otherwise 'dry' landscape once given over to cultivation but lacking stream courses. On air photos, the hollow is a distinct feature lying on the north side of a track and is surrounded by faint cultivation ridges.

David Leighton, RCAHMW, 4 August 2009