The main door of Santo António, in a perfect round arch, between two turrets, is defended by a barbican, in which the Porta da Vila is located, in a pointed arch. Inside, in the Plaza de Armas, it is possible to observe the adaptations of the accesses and the platforms intended for artillery.

It has two doors, in a perfect round arch, between prismatic cubes, interconnected by the structuring way of the city, the main door being flanked by two prismatic cubes and reinforced by barbican, both represented in the drawings of Duarte de Armas. The fence also integrates the SO. a breastplate to protect a source of water supply, the king's well, and, almost to the O., a tall tower with outer faces with a semicircular section in the center.