The church of Santiago de Jaca is a Romanesque Catholic temple with three naves that were originally finished off to the east by apses that have now disappeared.
The entrance to the temple was located in a portico under the tower, to the west. The pillars of the portico, the north and south walls and remains of the presbytery are preserved.
In the bell tower, the level of the extension of the original body can be clearly seen: the first body has false horseshoe twin windows, its old cornice and its corbels; and above, a second body that houses the bell tower.
The head of the church is covered by a groin vault between doubled arches, while the central nave is covered by transverse arches, except for the second section.
The current measurements are 30 x 26.5 meters but with the apses it could be about 40 m., important measurements at that time in the history of the city of Jaca.