attack. They were originally built in the 15th century, although large portions of the walls were rebuilt by the Hospitallers or in modern times. The northern walls include the remains of a collapsed medieval wall tower, a blocked-up sally port, a lookout post and some walled-up windows. Masonry revetments are built in depressions within the cliff face below the northern walls. 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. The bastions are linked together by curtain walls. The one between St. Martin's Demi-Bastion and St. Michael's Bastion contains the Main Gate, a modern arched opening and a clock tower. The wall between St. Michael's Bastion and St. John's Demi-Bastion is known as St. Philip's Curtain, and its upper part contains slit-like openings which open into a series of magazines which are now used as craft shops. These rooms support a walkway along the ramparts. Cavaliers were also built close to each demi-bastion. St. Martin's Cavalier is located between the medieval enceinte and St. Martin's Demi-Bastion, and it is only partially intact, its upper portions having been pulled down. St. John's Cavalier, which is found near St. John's Demi-Bastion and the rear of the cathedral, was completed in 1614. A freestanding room was constructed on its roof in 1701 for use as a gunpowder magazine. A pentagonal artillery battery known as the Low Battery is grafted below the walls at the easternmost extremity of the fortress, close to St. John's Demi-Bastion. The southern perimeter of the Cittadella is surrounded by a ditch, which originally extended from St. Martin's Demi-Bastion to the Low Battery but now begins at St. Michael's Bastion due to 19th-century alterations. A covertway with a single place-of-arms runs along the ditch. A steep glacis was located outside the covertway, but this has been built up. A small triangular ravelin stands near the entrance to