The design of the Fortress of Mazagan is a response to the development of modern artillery in the Renaissance. The star form of the fortress measures c 250m by 300m. The slightly inclined, massive walls are c 8m high on average, with a thickness of 10m, enclosing a patrolling peripheral walkway 2m wide. At the present time the fortification has four bastions: the Angel Bastion in the east, St Sebastian in the north, St Antoine in the west, and the Holy Ghost Bastion in the south. The fifth, the Governor's Bastion at the main entrance, is in ruins, having been destroyed by the Portuguese in 1769. Numerous colonial-era Portuguese cannons are still positioned on top of the bastions. The fort had three gates: the Seagate, forming a small port with the north-east rampart, the Bull Gate in the north-west rampart, and the main entrance with a double arch in the centre of the south rampart, originally connected to land via a drawbridge. A ditch, c 20m wide and 3m deep, formerly filled with seawater, surrounded the fort. During the time of the French Protectorate the ditch was filled in with earth and a new entrance gate was opened leading to the main street, the Rua da Carreira, and to the Seagate. Along this street are situated the best preserved historic buildings, including the Catholic Church of the Assumption and the Portuguese cistern. The Citadel The Citadel, located at the heart of the walled city, was the first permanent Portuguese construction on this site in 1514. It is a building with a rectangular floor plan measuring about , with three major rooms around a central space and four towers (one at each corner). The southern El-Briya Tower (originally known as al-Burayja) was of local, pre-Portuguese origin and it was here that the Portuguese first took refuge when they arrived in 1502. One of the northern towers was later re-purposed as the base of a 19th-century minaret built for the nearby mosque. The cistern is located beneath the Citadel. Portuguese cistern The semi-subterranean chamber has a roughly square plan measuring around per side, was constructed with five rows of five stone pillars and columns. The chamber is built in a late Gothic style known as Manueline, with a vaulted ceiling of brick masonry and stone ribs. Its original function is not clear. It may have been an armory, barracks, or granary, but