The medieval city walls, built in several stages between the 13th and the 16th century, were torn down after the French annexation in the 17th century. However, four towers escaped destruction. The "Tour des Sorcières" ("witches' tower"), which served as a gate and a jail, is the tallest. The "Tour de l'Horloge" ("clock tower") was also originally part of a gate. The clock and the elaborate roof were added in 1614. Two much smaller towers can also be seen, one near the Ill river and another integrated into a later house. All these remains date from the 13th century.