Built in the twelfth century on the banks of the River Sar, this, the collegiate church of St Mary, is a fantastic example of Galician Romanesque architecture. One of the principal features of the exterior is the robust buttresses, built between the seventeenth and eighteenth centuries to protect the walls. Inside, the beautifully proportioned space is given a sense of instability by the inclination of the columns towards the lateral aisles. The Romanesque cloister - the only one in the city of this style - can be accessed by way of the vestry.