This enormous 7th-century basilica honours Thessaloniki’s patron saint. A Roman soldier, Dimitrios was killed around AD 306 at this former Roman bath site by order of Emperor Galerius, infamous persecutor of Christians. The martyrdom site is now a crypt; Dimitrios’ remains occupy a silver reliquary inside. The Ottomans made Agios Dimitrios a mosque, and plastered over frescoes that were again revealed after the 1913 Greek reconquest. While the city's fire of 1917 was very damaging, five 8th-century mosaics survive.

　　Look for the unusual ciborium (hexagonal shrine) and precious 5th-century mosaics from earlier churches erected here.