In 1236, Córdoba was captured by King Ferdinand III of Castile in the Reconquista, and the mosque was turned into a Catholic church. Alfonso X oversaw the construction of the Villaviciosa Chapel and the Royal Chapel within the mosque. The kings who followed added further Christian features, such as King Henry II rebuilding the chapel in the 14th century. The minaret of the mosque was also converted to the bell tower of the cathedral. It was adorned with Santiago de Compostela’s captured cathedral bells.
The most significant alteration was the building of a Renaissance cathedral nave right in the middle of the expansive structure. The insertion was constructed by permission of Charles V, king of Castile and Aragon.
The Great Mosque's conversion to a Christian Catholic church, the Catedral de Córdoba, may have helped to preserve it when the Spanish Inquisition was most active. Artisans and architects continued to add to the existing structure until the late 18th century.