Located on the right bank of the mouth of the River Lima, at the western end of Viana do Castelo, the Fort of Santiago da Barra is a structure with an irregular star-shaped plan, consisting of four bulwarks. Entrance to the fortress is via a wide bridge, suspended over the moat that surrounds the structure. The Forte de Santiago da Barra currently houses the headquarters of the Regional Tourism Entity of Porto and North of Portugal and the Hotel and Tourism School of Viana do Castelo. This monument is open to visits.

Located by the sea, it is thought that the first fortification placed on the mouth of the river Lima dates back to the reign of King Afonso III (13th century). However, the oldest safe date dates back to the 16th century. XV, when a fortress was built there that would have been completed in the following century, already during the reign of D. Manuel I, as suggested by some Manueline architectural elements, namely the so-called “Torre da Roqueta”, located in the southwest bastion of the current fortress.
At the end of the 16th century, the fortress was subject to successive improvement works, having already been under Spanish domination, during the reign of Filipe II (Filipe I of Portugal), that the current polygonal fortress was built, from a design by Filippo di Terzi, the most famous designer of military buildings at the time.

Source: https://www.visitportugal.com/pt-pt/content/forte-de-santiago-da-barra