The medieval castle mound known as Castell Prysor is formed from an outcrop upon a spur projecting from the hillside above the Prysor valley. There are ruins of several buildings and terraces and enclosures, to the west and east. This is thought to have been a princely court, or llys. A later building (NPRN 28274) occupies an earlier building platform.

This is one of several instances in Merioneth where an apparently unfortified mansion or court is associated with a castle mound, for example Crogen (NPRN 306558) and Rug (NPRN 306598). At Aber in Caernarvonshire a thirteenth century court (NPRN 309171) was excavated at the foot of a castle mount (NPRN 95692).

A natural rock boss has been formed into a high steep sided mound by the addition of a mass of stones set in clay, retained by a massive spiralling wall. The resulting mound is in the region of 40-50m across and 15-25m high, with a level summit 8.0-13m across. Pennant noted traces of a round tower in the late eighteenth century (Tours ii, 111-12). The castle mound has no certain outworks. Pennant's notice of 'many Roman coins & urns' being found here may be no more than a figure of speach.

Sources: Gresham and Hemp in Archaeologia Cambrensis 100 (1949), 312-3
de Lewandowicz in Archaeology in Wales 38 1998), 36-42
History of Merioneth II (2001), 408-9

John Wiles, RCAHMW, 09.07.07