It is located in Castelo Santiago da Barra, city and municipality of Viana do Castelo, Northern Portugal
 
The Fort of Santiago da Barra, located next to the sea, is believed to be the first fortification placed on the edge of the Foz do Rio Lima dating back to the reign of D. Afonso III (13th century).

The first fortification placed on the Foz bar of the Lima river dates back to the reign of D. Afonso III, although the oldest dates back to the 15th century when a fortress was built there that would have been completed during the reign of D. Manuel I, as suggested by some Manueline architectural elements, namely the so-called "Torre da Roqueta" located in the southwestern bastion of the current fortress.

At the end of the 16th century, the fortress was subject to successive improvement works and it was already under Spanish domination during the reign of Philip II (Philip I of Portugal) that the current fortress with a polygonal plan was built based on a project designed by Filippo di Terzi, the most famous designer of military buildings at that time.

The Fort of Santiago da Barra is an irregular star-shaped structure made up of four bastions: two facing the land called “São Filipe” and “São Pedro”, one facing the river called “São Rafael”, and the one facing the sea called “São Gabriel”.

The Fortress is made up of trapezoidal walls with triangular bastions at the apexes facing the earth, and some with circular guardhouses at the corners.

Entry to the fortress is via a wide bridge suspended over the moat that surrounds the structure that leads to a perfectly round portal flanked by pilasters surmounted by the coat of arms of D. João de Sousa, governor of the fort in 1700, and topped on the cornice by the coat of arms of Portugal.

Inside are the old Cavalry, Sergeant's and Governor's barracks, and they are all rectangular in plan, but of different dimensions.

The interior is accessible through a vaulted tunnel that leads to the parade ground, and in front of us is a rectangular building with three registers, and an elevation with three doors, the main one being a round arch topped with a cartouche and flanked by columns surmounted by half-relief balusters topped by the royal shield.

On the right side of the square there is the “Chapel of Santiago” with a longitudinal plan with a rectangular nave and main chapel, and having a gable facade that is torn by a straight lintel door flanked and topped by three rectangular windows, the lateral ones being larger, and having a bell tower on its right.

The Fort of Santiago has a pentagonal plan consisting of walls with a trapezoidal profile, and reinforced by triangular bastions at the apexes facing the earth, with circular plan guardhouses at the apexes.

Entry to the fortress is via a wide bridge over the moat that surrounds it, and leads to a portal with a round arch flanked by pilasters surmounted by the coat of arms of D. João de Sousa, governor of the fort in 1700, and topped on the cornice by the coat of arms of Portugal.

On the embankment accessed by a vaulted corridor stands a main building with a rectangular plan of three registers with an elevation rhythmic by three portals, the main one being framed by a round arch topped with a cartouche and flanked by columns topped by balusters in half relief, topped by the royal shield.

The side portals have a round arch frame without decoration, windows were opened along the entire façade on both registers.

The building also has mansard windows, to the north is the “Chapel of Santiago” with a longitudinal plan with a rectangular main chapel, and a frontispiece ending in a gable with a bell to the right.

To this is located the magazine building with a quadrangular floor plan with a perfect round portal surmounted by the coat of arms of Portugal and topped with a triangular gable.

Integrated into the southwest area of ​​the fortress located on a terrace that forms in the second register stands the so-called “Torre da Roqueta” with entry from the wall via a ramp.

The Torre da Roqueta, flanked on the outside by four small towers, is surrounded by a small moat, and has a rectangular body with two registers, a terrace with arches and the arms of King D. Manuel carved into the façade.

In the fortress, the “Roqueta Tower” stands out, in the Manueline style of architecture, the oldest construction, and in it are the Cross of Christ and the Manueline armillary sphere.

The structure of the fortress is of military architecture, and the pentagonal wall presents a triangular fortress system, and was designed by Filipe de Terzi and the date 1596 can be seen inside.
The Classification of the Fort or Castle of Santiago in Viana do Castelo
 
The Fort or Castle of Santiago in Viana do Castelo is classified as a Property of Public Interest.