The Romans built a lighthouse (Pharos) on this site, and a church (St Mary de Castro) was later founded by the Saxons. William the Conqueror reinforced the fortifications, and the superb keep was added around 1180, with a surrounding wall. The Constable's Tower dates from the 13C, and the underground galleries were extended during the Napoleonic era and again during the Second World War. Sound effects and other paraphernalia – at times macabre – lend the site an almost Orwellian atmosphere.