Basilica di San Lorenzo, Milano

This guide to the Basilica di San Lorenzo in Milan opens inside an octagonal chapel older than the church around it, likely raised as a private mausoleum for Emperor Theodosius's family, possibly his daughter Galla Placidia, though historians still argue over who ordered it built. It follows the fourth-century mosaics surviving in the dome, and the sixteen Roman columns salvaged from an emperor's bathhouse that give the church its local name, San Lorenzo alle Colonne. You'll also hear about the martyred priest whose remains later came to rest in that same imperial chapel, and about the open ground behind the basilica that Milan put to a very different use for centuries.