Seized by the invaders, castle and town were later retaken in 1231 by Prince Llewelyn ap Iorwerth, who burned the fortress and slew its garrison.
It was only the alliance of Montfort with Llewelyn of North Wales that brought the earl of Hereford back to his allegiance.
Another castle, built in the same century, on the east bank, was held direct by the lords of Glamorgan, as the westernmost outpost of their lordship. It was frequently attacked by the Welsh, notably in 1231 when it was taken, and the town demolished by Llewelyn ab Iorwerth.
At first he was a friend of King John, whose illegitimate daughter, Joanna, he took to wife (1201); but the alliance soon fell through, and in 1211 John reduced Llewelyn to submission.