1. A defended enclosure, c.100m by 60m, set on a north-east facing hillslope, defined by a bank and ditch, except to the north, where a weak bank is said to have existed.

(source OS495card; SO02SW2)

J.Wiles, RCAHMW 26.07.02

2. Further source: RCAHMW Brecknock Inventory, Part ii, 1986, p. 60

3. Earthworks identified on the ridge of Allt Du above Plas y Gaer appear to be an unusual form of Iron Age defensive work straddling the ridge which ultimately gives access to the summit of Pen y Fan above. It may be that these banks protected Plas y Gaer from unwelcome visitors from the south-west, or perhaps performed a ceremonial function on journeys between the lowland defended enclosure and the mountain summit. See NPRN 421809.

T. Driver, RCAHMW, Oct 2016