Château Gaillard

Richard the Lionheart built this fortress above the Seine in just two years, 1196 to 1198, to guard Normandy against the French king. It packs three separate enclosures, each with its own walls, behind a ditch 20 meters wide, and it was one of the earliest castles to use machicolations, the overhanging openings for dropping missiles on anyone at the wall foot. It is also the classic lesson in how layered defenses fail. Philip II took it in 1204 after a long siege, and his men got inside through a latrine passage. Walking the ruin, you can trace each enclosure in turn and see how an attacker had to repeat the whole effort at every line, and how one overlooked opening undid it.