The Fort du Château was built on the steep rock which dominates the Cité Vauban, first in reinforcement then in place of the medieval fortified castle which occupied the spot in the time of the Dauphins and which included a 787ft (240m) long wall with four towers, a large square keep, a housing building and a chapel. The only element built by Vauban, the powder magazine, has earned the site registration on the UNESCO World Heritage List.