Castell Du

, also known as Sennybridge Castle or Castell Rhyd-y-Briw, is located approximately eight miles west of Brecon in Powys, Wales, and is believed to be the work of Llywelyn ap Gruffudd, Prince of Wales. Its history is largely obscure, but a reference to a castle at Rhyd-y-Briw in a document of 1271 is believed to refer to the fortification, and it is not unreasonable to assume that work commenced on it during Llywelyn's triumphal years in the 1260s.