Today the Church of Agios Dimitrios is probably the most remarkable church in Thessaloniki (St. Demetrios is the Thessaloniki city patron). The first church on this place was built already in the 4th century when it replaced old Roman baths. According to a legend, St. Dimitrios was held prisoner there before the emperor Diocletian sent him to his death. In the 5th century, the church was enlarged to become a three-aisled and then in the 7th century a five-aisled basilica - at that time, it was the city’s most important sanctuary.

The basilica is famous also for its six large mosaics from the beginning of the 8th century, depicting St. Dimitrios with children. Yet many of the mosaics were destroyed during 1493-1912 when the church was a mosque. Another event that had a devastating effect on the church was the great firre in 1917. Today most of the original church ornamentation is deposited in the Thessaloniki Museum of Byzantine Culture.

During 1930-1950, excavation works took place in the undergound part of the church, uncovering the remains of Roman baths. Today this crypt is the site of a small museum with findings from the period of 5th-8th century.