Rotunda of Galerius Thessaloniki

In AD 306 Roman emperor Galerius built this harmonious 30m-high dome, comparable to Rome's Pantheon and possibly intended as his mausoleum. Marking the momentous arrival of Christianity as the religion of Empire, the Rotunda became Thessaloniki's first church (Agios Georgios; observe dragon-slaying St George above the door). The Ottomans in turn made it a mosque (hence the restored minaret), but since the Greek reconquest of 1912 it has served both sacred and secular purposes. The architectural harmony of the ancient building, plus its remaining mosaics and frescoes are the main draws for today's visitors.