It was not the first stronghold to occupy this strategic site: it was built over the stronghold of Dafydd ap Gruffudd, the Welsh leader crushed by Edward in 1282.
Ar un adeg roedd y castell yn gartref brenhinol Dafydd ap Gruffudd ac yn dilyn cyrch ganddo ar Gastell Penarlâg gerllaw ysgogwyd Edward I, brenin Lloegr, yntau i drefnu ymosodiad ar raddfa fawr.