This defensive system was first created in the 13C and then reinforced in the 15C. The main gate, that of Terra Firma, is reached by a majestic stair-bridge (1863) and guarded by a 13C square tower. It is doubled by a Baroque triumphal arch (1650). The rampart walk leads round the city, past the palace and the port protected to the southwest by the governor's small and large towers. The wharfs are also guarded by a square tower, Kanavelic tower (15C).