Chepstow Castle was originally an 11th century earthwork and stone enclosure fortress, founded by William fitz Osborn. Standing against the steep banks of the River Wye, it was defended by deep rock-cut ditches. In 1081, King William I founded the impressive stone keep and baileys castle, which now stands on the site. After 1189, the castle was extensively altered in the construction of a palatial stronghold, by William Marshal, his five sons and Roger Bigod, earl of Norfolk. An exhibition in the castle, houses the oldest castle doors in Europe and in the town, are the Port Wall and the Town Gate. 13 miles north-west is Usk Castle.