The collegiate church of Santa María del Sar is a Romanesque Catholic temple that was declared a National Monument in 1895.

The building was originally built and conceived to serve as a retreat house for the canons regular who were governed by the rule of Saint Augustine. Despite this, it ended up becoming a landmark on the Pilgrim's Route to Santiago de Compostela.

Munio Alfonso was a former member of the chapter of the cathedral of Santiago, who worked as a collaborator of bishop Diego Gelmírez, who proposed him in 1112 as bishop of Mondoñedo, a post he held from that year until the time of his resignation in 1134. When he resigned as bishop, he decided to found a small monastery, governed by a community of Augustinians, and for this purpose he bought a plot of land on the outskirts of the city and on the banks of the river Sar. But when he died before finishing the work, he entrusted it to his friend, also bishop Diego Gelmirez.

With the foundation of this monastery, the first Augustinian community of Galicia was constituted, joining the new and reforming European spiritual currents. The community had the support of the Crown, which granted donations, exemptions and privileges to the Augustinian community throughout the Middle Ages.

However, in spite of all these donations and aggrandisements, during the 16th century, coinciding with the priory of Jácome Álvarez, archbishop of Tarsus, a period of decline began. It was then that the priory was transformed into a collegiate church. Furthermore, the institution was further weakened by the replacement of the canons of St. Augustine by secular clergy in 1548, which led to the loss of the influence of the power of the Augustinian community.

In the second third of the 17th century, the deterioration of the church building began and quickly spread to the cloister and the rest of the monastery buildings.

One of the most important economic collaborators in the recovery of the monastery of Santa María de Sar was the powerful monastery of San Martín Pinario. The improvement in the economic situation of the monastery meant that during the 18th century it was enriched with works of Baroque gold and silverwork from Compostela at the time, including the sacred vessels of the church, the parish cross, reliquaries and censers, among other pieces that form part of the monastery's museum.

Later, during the 19th century, and as a result of the 1851 concordat between the Spanish State and the Holy See, the collegiate church underwent a new period of decline, becoming just another parish within the Archdiocese of Santiago de Compostela.

The ground plan of the church is basilica-shaped with three naves that are separated by compound pillars (with vegetal decoration) on which the barrel vault that covers them rests. At the end of each nave, an apse of different shapes was built, the central one being polygonal, while the lateral ones are semicircular. The interior lighting is achieved through lateral windows and the presence of a rose window in the doorway. The main façade is characterised by its sobriety.