This is a small promontory fort crowning the highest northern spur of an isolated hill. It rests above steep slopes except on the south, where it faces the relatively level hilltop. The site was extensively excavated in 1954-9 when much early medieval material was recovered. The excavator considered this to be an early medieval fort occupying the site of an open Iron Age settlement, all overlain by a massively enclosed earthwork castle. The many caveats attending this interpretation make it problematic.
The fort is a roughly oval 0.08ha enclosure mostly defined by a broad ditched rampart with a palisade on the north. The entrance was at the north-west extremity and would have been approached along the rocky spine of the steep slopes below. There are three additional lines of ramparts on the south, one of which may have continued around the west side. The inner rampart was revetted in stone and appears to have had a timber-framed breastwork. The second rampart, also ditched, is relatively insubstantial. The two outer ramparts are again massive and appear to have been conceived as a pair, the inner again stone revetted. Traces of two rectangular buildings up to 7.5m wide were recorded in the interior.
The finds were mostly early medieval, but also included Roman material and fragments of a twelfth century pot. The ramparts overlay deposits containing Iron Age pottery. The fort does not resemble a medieval castle, but rather a later Prehistoric style hillfort and may have been established as late as the Roman period. It was clearly occupied into the early medieval period and the internal buildings could relate to this or else to an ambiguous phase signalled by the twelfth century pottery.
A bank and ditch (Bank V) running south from the fort is an old field boundary shown on the 1st edition OS County series (Glamorgan. XLVII.5 1880) and may have been connected with the enigmatic 'causeway'.
There is a second defended enclosure 130m away on the southern edge of the hilltop (NPRN 307785).
Sources: Alcock 'Dinas Powys' (1963), University of Wales Press
RCAHMW Glamorgan Inventory III.1a The Earlier Castles (1991), 95-100
John Wiles 14.02.08