The Rotunda is a huge round building of brick, with walls six metres thick and a dome spanning about twenty-four metres, and it has been standing since the early fourth century. It was probably built for the Roman emperor Galerius, who made Thessaloniki one of his capitals and who may have intended it as his mausoleum, though in the end he was buried elsewhere. Around AD 400 it was turned into a church, with a ring of mosaics added to the dome and the walls, and a tall apse added on the east side. The mosaics, of saints in prayer before gold and colour backgrounds, survive only in part, but the few that remain are among the finest in the Christian world.
In 1590 the building became a mosque, with a minaret that still stands in the courtyard, the only one left in the city that has survived from the Ottoman period, and the Greek state later used the building as a church and then as a museum. It has withstood earthquakes for seventeen centuries, which is remarkable, and the restoration work continues. It is a rare monument that shows Roman, early Christian and Ottoman layers in a single structure, and it has become a symbol of the city. The Arch of Galerius stands a few hundred metres south on the same axis, carved with scenes of the emperor's victories over the Persians.
Be prepared for the traffic. The Rotunda sits at the edge of a busy road junction near the Egnatia axis, with heavy flows of cars, motorbikes and buses, and parking is difficult. Choose a side street and stroll. The pavements around the monument are wide and open, with trees and benches, and they are popular with students and locals in the evening. In winter, a cold north wind called the vardaris can blow down from the Balkans, which is a reminder that the city is not as Mediterranean as it seems.
Fuel is easy to find on the main avenues, and the nearby streets are filled with cafes and restaurants. Take the chance to try a koulouri, a sesame ring, from one of the street vendors, or a cup of salep, a hot milky drink, in winter. The best time to see the interior is in the morning, when the light from the high windows brings out the colours, and the dome seems to float above you. Check the opening hours, which vary, and remember that you can walk around the outside at any time.