Founded by Pope Sixtus III (432-440), this is one of Rome’s four great basilicas, and has been remodelled many times down the centuries. Erected in 1377, its campanile is the highest in Rome. The façade (1743-1750) is the work of Ferdinando Fuga. The interior is breathtaking; note the beautiful 5C mosaics in the nave depicting Old Testament scenes, and also those decorating the apse and the main arch.