Dinefwr Castle is a ruined medieval castle in a dramatic and Romantic situation upon a high wooded ridge above the meandering Tywi. The castle is thought to have been founded in the later twelfth century by Rhys ap Gruffudd, the Lord Rhys, and became known as the traditional capital of Dyfed. The visible remains date from the thirteenth and earlier fourteenth century. It was still maintained in the earlier fifteenth century, but may have been replaced by Newton House (NPRN 17603), a little way to the north, as early as the later part of the century. By the later seventeenth century it had become a Picturesque attraction in Dinefwr Park (NPRN 266170) and the top of the great tower was taken down and replaced by a summerhouse. The castle ruins have now been consolidated for public view.
The castle consists of two enclosures defined by deep rock-hewn ditches cutting across the summit of the ridge. The inner enclosure has a high curtain wall and is approached by a lower walled barbican. The great round tower, some 12m across, is now a two storey stump crowned by the remains of the seventeenth century summerhouse. There are ruins of fine towered lodgings along the north-east curtain and there is a smaller round tower at the northern angle.
Two boroughs were associated with the castle. The upper town, thought to have been sited on the castle ridge, was first recorded in 1281. The lower town, Newtown or Drenewydd, where Newtown House now stands, is first mentioned in 1297.
