Rotonda

The Rotunda is the oldest of Thessaloniki's great monuments, a massive brick drum built around 300 AD as part of Emperor Galerius's palace complex, perhaps as a temple or an intended mausoleum. It was turned into a church in the early Christian period, when its dome was covered with glittering mosaics, then into a mosque under the Ottomans, which is why the city's only surviving minaret stands beside it.

It is part of the Paleochristian and Byzantine Monuments of Thessaloniki, a UNESCO World Heritage Site since 1988. Inside, look up at the surviving mosaic panels of saints set against gold and architecture. The Rotunda sits a few minutes' walk north of the Arch of Galerius; check the day's hours, as it is sometimes used for events.