In order to strengthen the city's defenses. It was located in the northeast corner of the perimeter of the wall, near the road that led to Venice, in an undeveloped area.
The focal point of the castle consisted of a roca, or reduced, consisting of a large quadrant measuring about 2,180 square meters with four huge circular towers at the corners, connected by curtain walls. Towards the south, on the other hand, the castle opened on an area of 14,000 square meters used for garrison housing, food deposits, weapons, stables and other services. Surrounded by walls, with a fortified gate, it had defensive towers in the corners, two circles and semi-circular. Everywhere ran a wide trench whose effects can still be guessed despite the work of Reem
