The remains of the medieval castle at St Fagans include the southern part of a stone curtain wall, thought to have originally encompassed a sub-circular, or oval enclosure, between 45 and 50m in diameter. The enclosure is currently overlain by an Elizabethan mansion (Nprn 19909), with part of the surviving curtain serving to define its forecourt. The medieval work is thought to be a thirteenth century remodelling of an earlier ringwork. The medieval castle was derelict by around 1530.

Source: RCAHMW 1991 Glamorgan III.1a 'the Earlier Castles', 341-6.

J.Wiles, RCAHMW, 05 January 2003