Ravenna is on Italy’s tourist map for one reason: its 1,500-year-old churches decorated with best-in-the-West Byzantine mosaics. While locals go about their business, busloads of tourists slip in and out of this town near the Adriatic coast to bask in the glittering glory of Byzantium, the eastern Roman Empire.

Imagine that it’s AD 540. The city of Rome has been looted, the land is crawling with barbarians and the Roman Empire is crumbling fast. Into this chaos comes the emperor of the East, Justinian, bringing order and stability — and an appreciation for mosaic art.