On June 30, 1236, King Ferdinand III of Castile entered the city of Córdoba, putting an end to the five-month siege that his troops had staged around the square. The Spanish Reconquista of Islamic Andalusia was advancing, and Córdoba, capital of the Umayyad caliphate in the 10th century, was the latest to fall. It had once been the brightest and most populous city in Al Andalus. It was also home to one of the world’s marvels of architecture: the Aljama Mosque.
A day before the king entered Córdoba, after the Muslims had already abandoned it, a group of Castilians left the place where they were encamped, entered the walled city through the Algeciras Gate, and went to the Great Mosque. They placed a cross and a flag of Castile atop the minaret. A few hours later, the bishop of Osma sanctified the building and celebrated a dedication mass after consecrating the altar. In a few moments, the magnificent Aljama Mosque had become a Christian cathedral.
The new beginning decreed by Ferdinand III in 1236 was not the first transformation of the site at the foot of the Sierra Morena in southern Spain. Legend has it that when Romans founded Córdoba in the second century B.C., they built a temple there dedicated to Janus, the two-faced god of new beginnings. Some 800 years later, the Visigoths took control of much of the Iberian Peninsula. In A.D. 572, Visigothic King Leovigilido captured Córdoba, and a Christian basilica was built there.