The vaulted ceiling of the Tour de Constance in Aigues-Morte consists of 12 arteries with ribbed branches. The upper platform of the tower is topped by an openwork wrought-iron cage itself capped with a conical lead roof. In the Middle Ages, this shelter was used to protect the lookout fires making the tower both a watchtower and a lighthouse. The Tour de Constance, built for the defense of the city with the rest of its ramparts, is 72 ft (22 m) in diameter, and its lantern rises to 108 ft (33 m) high. The Salle des Chevaliers (knights’ room), on the first floor, served as a prison on several occasions.