The outer walls of the castle are Roman, built in the third century AD, and enclose about ten acres. At that time the castle was much closer to the sea than it is now. It was here that, in September 1066, one Duke William of Normandy landed. The following month he defeated Harold in the battle of Hastings. The Conqueror conferred the Rape of Pevensey on his half-brother Robert of Mortain, who began construction of a castle within the Roman walls. Further fortifications were added at the time of the Spanish Armada threat, and again during the Second World War, with pill boxes disguised as ancient masonry.