Gelli-nedd univallate fort is located on the summit of a limestone ridge. The plan is oval in form measuring internally 60m northwest to southeast by 45m, an enclosed area of approximately 0.41ha. Most of the west side is formed by a precipitous cliff where no artificial defences were required, whereas the remaining sides comprise a rampart of limestone rubble, partly grass-grown, with an external rock-cut ditch around the north and south. The rampart is strongest on the north where the outer scarp rises to 3m, the inner scarp to 0.9m. The entrance is a simple gap measuring 3m wide on the northeast.
D.J.Percival, RCAHMW, March 1985.