There are a complex series of earthworks at Cefnllys covering an area approximately 356m by 102m set upon a ridge in a loop of the River Irfon. They are thought to represent the remains of an Iron Age enclosure, a medieval town and two seperate castles. The castle to the north-east is thought to have been destroyed in 1262 and was replaced by the one to the south. This was commenced in 1267 and aerial photographs show a circular tower, c.10-12m in diameter, which stood at the centre of a rectangular walled court, c.35m square. There are also indications of round towers, c.5.0m across, at the northern and eastern angles, the latter apparently associated with an entrance. The southern castle was ruinous by the late sixteenth century. Other rectilinear banks and enclosures, some of which overlie elements of the defensive complex, are thought to represent a more recent farmsread.
Source: Brown 1972 (Rad. Soc. Trans. 42), 11-22.
J.Wiles, RCAHMW, 12 February 2004