This is a mosaic in Ostia Antica, the first Port of Ancient Rome, in Italy. Some say it's a mosaic of the second port of ancient Rome: Portus. I took an amazing course on Portus. The lighthouse, pictured above, was modeled after the great Alexandria Lighthouse in Egypt. The lighthouse sat in an artificial harbor. It was built on Caligula's ship that transported an obelisk to Circus Maximus.
This mosaic is in the Piazzale dell Corporazioni (The Square of the Corporations.) It is famous due to it's many trade references and mosaics. Walking through this square in Ostia Antica is really amazing. It's like looking at a picture book from back in time. There are mosaics from Africa and all over the world. It gives you a great idea of all the different trading companies and people that were a part of ancient Rome's trade.