San Clemente

A favourite with kids for its dungeon-like underground level, this 12th-century basilica is a three-dimensional Roman timeline, a church above a church above an even older Imperial building – a full 18 metres (60 feet) of Roman life separate the earliest structure from the one we see today. In 1857 the Irish Dominicans – who have run the church since the 17th century – began digs that unearthed the church’s fourth-century predecessor, and, beneath, an early Christian titulus (meeting place). The fourth-century structure was razed in the Norman sack of 1084, but the schola cantorum (choir), with its exquisite carving and mosaic decorations, survived and was moved upstairs to the new church, where it still stands. Also in the upper church is the 12th-century mosaic in the apse, still in Byzantine style but with a theological complexity unusual for its period. Against a gold backdrop, cobalt blues, deep reds and multi-hued greens make up the crucified Christ.