Krak des Chevaliers

A crusader showcase of walls within walls. The Knights Hospitaller took possession in 1142 and held it until 1271, and the fortress they built pairs an outer wall with an inner citadel, adding doubled walls, many towers and a huge sloping base, the talus or glacis, that made the walls far harder to breach. Its end shows that even the best walls depend on the garrison. Sultan Baybars began the siege in 1271, his sappers mined under towers and a tower collapsed on March 30, letting his troops into the lower ward. The defenders then received a forged letter ordering them to give up, and on April 8 asked for terms. It stands near Homs in Syria, so check current travel advice before planning a trip.