Polygonal construction, repeatedly enlarged and restored. The primitive sector corresponds to the tower, built by D. Manuel in 1502, which can be seen today at the SO angle of the fortress. However, the work proved to be insufficient in the course of the 16th century, in view of the development of the maritime movement and the siege of the invading enemy, who used increasingly sophisticated war techniques. So it was good to reinforce the defensive system along the coast. In relation to Viana and its port, it gradually strengthened itself from the fortress, as to the walled circuit and the respective artillery equipment: by 1568 in the time of D. Sebastião, and at the expense of the Viennese Senate, a quadrangular fence was erected. "roqueta" itself, involving the Manueline tower. The construction of the bastioned polygonal fortress comes during the Philippine reign in 1568-1593, with the project of Filippo Terzi. In 1652 there was a new transformation, and in 1700 the revelins were built.