Andrew Graham-Dixon and Giorgio Locatelli continue their exploration of Rome off the beaten track. In search of its Papal, Renaissance and Baroque history, they discover that it is visible all around them. As well as marvelling at the mosaics in the 12th-century Basilica di San Clemente, Andrew takes Giorgio to its deepest basement and an ancient Roman schoolteacher's classroom. Then it is on to a true architectural and civic wonder - the vast Testaccio Slaughterhouse.