Pevensey Castle was originally a post-Conquest earthwork fortress, founded by Duke William of Normandy in 1066. Occupying one corner of the largely intact oval walls, of the early 4th century Roman Saxon Shore fort of Anderitum, an early 12th century stone keep and bailey castle was built. During the reign of King Richard I, a twin-towered D-shaped gatehouse flanked the curtain wall and in 1372 the castle was given to John of Gaunt, duke of Lancaster. The coastline started to recede from the castle and by 1500 the site lost its importance and was abandoned to fall into disrepair. In 1588, with the threat of the Spanish Armada, the castle was strengthened and modernised and a gun emplacement, supporting two demi-culverins, constructed in the outer bailey. In May 1940, the castle was again refortified as a World War II observation and command post, with machine gun posts and non-standard rectangular pillboxs, camouflaged among the walls. 4 miles north is Herstmonceux Castle and 8 miles west at Milton Street is Burlow Castle.