Pevensey Castle was originally an earthwork improvised fortress, founded in 1066 by Duke William of Normandy. A late 12th century, stone keep and bailey enclosure castle, founded by King Richard I now occupies one corner of the largely intact walls, of the 4th century Roman Saxon Shore fort of Anderitum. By the 1220's, 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 9 miles west is Burlow Castle.