It sits in a traffic-free cobbled square at the heart of Trastevere where locals congregate around the central fountain and the odd magician or fire-eater entertains tourists. The legend goes that when Christ was born, a miraculous well of oil sprang from the ground where the church now stands, and flowed down to the Tiber all day. The mosaics on the exterior are from the 13th century and show Mary breastfeeding Christ, surrounded by 10 women with crowns and lanterns on a gold background. Inside is another patchwork of glittering gold mosaics featuring Pietro Cavallini’s relaxed Roman-style figures and a Madonna and Child with rainbow overhead. Set into the exterior of the church is a collection of fragments of classical sculpture, medieval tombs and inscriptions, including ancient pagan sarcophagi tablature.