In the southern half of Spain, in one of the oldest cities in the region, lies one of the most unique structures in religious history. Beginning in 152 BC, in a city that would become the capital of the Islamic Emirate and, for a time, the most populous city in the world, a sacred edifice was erected that has fascinated the public for generations. First, it was a temple built by the Romans, next it was converted to a Catholic church by the Visigoths and then it became an Islamic mosque built by Abd al-Rahman I in 784 AD before being altered in a way that has never been done…