It was founded by Bishop Jerome of Périgord, in the 12th century and completed in Romanesque/Gothic style in the 14th century. It is dedicated to Santa Maria de la Sede (Saint Mary of the See).
The apse houses a large cycle of 53 tables, 12 of which by the 15th-century Italian artist Dello Delli, depicting the life of Jesus and the Virgin Mary. A fresco of the Final Judgement is over them.
Juan Francés de Iribarren was organist at the Old Cathedral in 1717–1733.