The original Motte and Bailey castle lay a mile down-stream, but the Marcher lord Gilbert Fitz Richard de Clare built a fortress on its current site in 1110.
Mae'r castell Mwnt a Beili gwreiddiol filltir i lawr yr afon, ond cododd un o Arglwyddi'r Mers, Gilbert Fitz Richard de Clare, gastell ar y safle presennol yn 1110.