Standing in front of a huge, darkly glittering wall mosaic from the first years of the third century CE, I find myself drawn into a lost world. A ship is departing a port in Alexandria, Egypt, its sails billowing, sailors working the ropes, and to the left is a tall lighthouse.

This window into the Roman empire comes from the domus (or mansion) of Claudius Claudianus, a senator of African origin, who made his money in Mediterranean transport. It’s not hard to imagine that what I’m looking at is one of the many grain ships that provisioned ancient Rome from the Nile valley.