The castle at Rhayader is possibly that built by Rhys ab Gruffudd of Deheubarth in 1177. It was destroyed in 1190 by the princes of Maelienydd, rebuilt in 1194 and again destroyed. These events might have concerned the castle mound across the river (NPRN 304969). In about 1200 the powerful Mortimer family either rebuilt the castle of founded it anew on this site, only for it to be captured in 1202. It was stormed and destroyed in 1231 by Llywelyn ap Iorwerth of Gwynedd. This was the principal if not the only castle in the territory of Gwerthrynion. By 1304 it was the 'site of the ancient castle', although it may have continued to have some legal role as a manorial centre, being refered to as a castle in 1316. The borough of Rhayader was probably established in the fourteenth century (NPRN 309594).

The remains of the castle consist of a roughly rectangular platform about 50m north-east to south-west by 40m. It rests above headlong slopes or crags above the river on the north-west and southern sides, with a great rock cut ditch up to 10m wide and at least 4.0m deep, on the north and south-eastern sides. The entrance is likely to have been on the north side. There are indications of a bank or rampart on the eastern edge of the enclosure. Stone foundations are said to have been seen in the earlier nineteenth century.

Source: Williams in Archaeologia Cambrensis 3rd series IV (1858), 559-62
RCAHM Radnorshire Inventory (1913), 137-8 No. 565

John Wiles, RCAHMW 31 July 2007