A timber castle was built in 1093 surrounded on three sides by water. The round,
stone 75 foot keep, outer walls and towers were constructed between 1190 and 1245.
It was severely damaged after being captured in the Civil War but was repaired in 1880 and then restored in 1920's.
At the same time as the castle was being rebuilt in stone in the 13th century, the town was protected by a defensive wall with six towers and three gatehouses, part of which remains.