Cefnllys was a medieval town in Radnorshire (now part of Powys) in central Wales. Only St Michael’s Church remains standing, with mounds indicating the remains of new buildings existing previously the decline of the town in the 19th century. Close by upon the hill known as Castle Rock are the remains of what is known as Cefnllys Castle. Almost encircling the hill, church and remains of the town is the River Ithon which continues to Llandrindod Wells a Tiny over a mile away.
The ‘castle’ was actually two, built one after the supplementary at opposite ends of the hill by the English lord Roger Mortimer of Wigmore during his battles in the space of Llywelyn ap Gruffudd, Prince of Wales, for the cantref of Maelienydd. The first, at the north end, was built in 1242 and ruined in 1262 by Llywelyn. The second, at the south end, was built in 1268 and survived Llywelyn’s death, but was sacked by Cynan ap Maredudd during the revolt of Madog ap Llywelyn in 1294–5. It was ruined by 1588.
Cefnllys was a contributory borough to the Radnor Boroughs constituency in the English and British parliament from the Laws in Wales Act 1542 until the Redistribution of Seats Act 1885 In 1831 it comprised, besides the castle ruins, “three Farm Houses and one small Cottage”.
Coordinates: 52°15′21″N 3°20′25″W / 52.2559°N 3.3402°W / 52.2559; -3.3402