The Great Mosque of Córdoba (La Mezquita) was founded 785 CE. It was added to and expanded over the next two hundred years to make it the third largest structure in the Islamic world. The prayer hall (23,400 square meters) is filled with almost 500 hundred slender columns and superimposed striped arches; a forest sprouting from the marble floor. Previously the site had been occupied by a Christian church dedicated to Saint Vincent that had been built by the Visigoths around 500 CE. Before that, when Córdoba was a provincial capital in the Roman Empire, the site was occupied by a temple dedicated to Janus, the double-headed god of doorways and gates.