City walls and towers

Apart from being a defence barrier, it allowed a path between the fortress and the embattled towers through the internal communication trenches.
The external-escarpment walls are built with the traditional method of the double "shirt" (regular bricks filled with rubble and pebbles and kneaded with lime). 
The rectangular walls lay-out (112 m x 146 m) played a crucial defensive function together with the moat. Moreover, a system of internal patrol trenches ensured the communication between the fortress and its four towers.

Walls are about 5 m tall and up to 2.5 m thick. They surround the old town centre and are clearly visible on all four sides.

The northern side is presently smaller due to recent restoration works. Some stretches are private-owned but all of them can be visited from outside.
The architectonical structure of the castle reflected a precise hierarchy where each defensive element (towers, walls and fortress) had its own role. Each tower "gave orders" to the walls below. This meant that it had to defend walls but it could also decide to destroy them if they were conquered by the enemy. Similarly, the Cassero (the fortress) gave orders to the towers