In the 12th century, the arches of the tower base were filled with stone, and it was expanded with the addition of a chapel, The Chapel of the Holy Saviour. The chapel is covered with a vault forming a quarter of a sphere, and is used as a crypt for the sarcophagi of bishops and canons of the cathedral. These sarcophagi, set into niches in the walls, are covered with images of the persons and are surrounded by sculpted arches and decoration.