The oldest parts of the choir date from the second half of the 11th century. The building stands out not only because of its lofty location, but also because of its magnificent facade. Work has been going on on the three-aisled Romanesque nave since the 12th century.
At that time, a new building was created according to a plan that was outdated for the time, with a four-bay, barrel-vaulted nave with a huge transept, which also received vaults and galleries on the front side, and a long choir with a semicircular interior and a square exterior. Probably out of respect for the sanctity of the place, the choir shape of the previous building was retained. In the course of the 12th century the barrels were replaced by domes.
The increase in the number of pilgrims in the second half of the 12th century made it necessary to enlarge the church. The sacred character of the apse forbade expansion to the east where there was no lack of space. Therefore, the new building was extended to the west by two additional bays.
The important cathedral with its early Christian décor, some of which was probably derived from Islamic sources, was the victim of a radical and catastrophic reconstruction in the 19th century.
In a process in which each step inevitably led to the next, the architect Mallay reconstructed the crossing dome and crossing tower, the last two domes of the nave, the southern arm of the transept and the upper part of the northern one, from 1884 onwards , finally the two western bays and the facade. From 1865 to 1866 the choir was demolished and arbitrarily reconstructed.
Between 1844 and 1888 it was the turn of the tower built in the 12th century east of the choir. Its restoration meant rebuilding from the second floor. Ultimately, only the third and fourth nave yoke escaped the serious intervention. They have been restored but not reconstructed.