The southern perimeter of the city consists of a 17th-century bastioned enceinte which was built by the Hospitallers. A large arrowhead-shaped bastion known as St. Michael's Bastion is built at the southernmost end of the city, while two demi-bastions – St. Martin's and St. John's Demi-Bastions – are located at the west and east ends of the city. Flat-roofed échauguettes are built on the salient of each demi-bastion. St. Michael's Bastion also had an echaugette but this was replaced by a clock tower in 1858. A small gunpowder magazine is located at the junction between St. John's Demi-Bastion and the medieval enceinte.