The cathedral-sized Red Hall, sometimes called the Red Basilica, is thought to have been built by the Romans as a temple to the Egyptian gods Serapis and Isis in the 2nd century AD. It’s an imposing-looking structure with two domed rotundas; visitors can enter the southern rotunda but not the main temple (currently being restored) or the northern rotunda. The southern rotunda was used for religious and cult rituals – look for the huge niche where a cult statue would have sat.
Originally, this must have been an awe-inspiring place. In his Book of Revelation, St John the Divine wrote that this was one of the Seven Churches of the Apocalypse, singling it out as the ‘throne of the devil’. In fact, the building is so big that the early Christians didn’t convert it into a church, but in the 5th century AD built a basilica inside it instead.