Situated on the highest part of an oak forest with the same name, it was built on the site of a Castro (Celtic Settlement). Consecrated in 1102 by Archbishop Xelmírez to house the relics of the saint-co-patron of the city - taken there from Braga (Portugal). The building was donated by the Counts of Altamira to the Local Council in 1546. It only conserves the doorway, some corbels and a window from the Romanesque period. The present-day building is a 17th-century reconstruction. It stands on a rectangular ground plan, with granite masonry walls and a slate gable roof. The facade shows a doorway with double semi-circular arches supported by columns on each side, with smooth shafts and decorated capitals. A window substitutes the tympanum. Above the doorway, there is a semi-circular arched window. A Gothic cross tops the construction. Adjoining the west side, the 19th-century bell gable and the sacristy. This church is mentioned in the Calixtine Codex and was the site chosen by Doña Urraca to set up camp when she besieged Santiago in 1116.