Like Ayia Sofia, Ayios Dimitrios was heavily restored -- in fact, almost entirely rebuilt -- after the fire of 1917. Consequently, this is a church with an imposing history, some fine mosaics, but very little soul. That's a shame, because the story of Dimitrios is stirring: In the 4th century A.D., this site was occupied by a Roman bath, a corner of which was used as a makeshift jail. In A.D. 303, one of the prisoners, young Dimitrios, got into trouble by preaching the Gospel. Dimitrios not only refused to renounce his faith but seems to have converted another prisoner, a gladiator who fought and killed Emperor Galerius's favorite gladiator. Galerius was furious and had Dimitrios executed. Soon, a shrine here commemorated the martyred Dimitrios; then a small church was built, and in the 7th century A.D., the church was enlarged into its present five-aisled basilica form. After the 1917 fire, the church was rebuilt on and off from 1926 to 1949. You can still see scorch marks from the 1917 conflagration on some of the interior walls.
Almost all the mosaics here are restorations of what was lost in 1917, but a cluster from the 5th to 7th centuries A.D. survives. Look for the lovely, original portrait of the boyish saint with two young children, and the representation of Demetrios with the church founders. (You can see other mosaics salvaged after the fire on display in the Museum of Byzantine Culture.) The crypt, which is down a narrow, twisting staircase, reveals several small anterooms and remains of Roman baths; the crypt sometimes functions as a small gallery. Particularly venerated are the spot where Dimitrios is believed to have been martyred (and where a vial of blood, believed to be the saint's, was found) and the spot with a holy-water font. For centuries, the faithful noted a sweet scent at the font, and believed that myrrh, or perfumed fluid, flowed from the saint himself. As you leave the church, have a look at the chapel of St. Euthymius, built into the wall of Ayios Dimitrios. The 14th-century frescoes in the little chapel have all the verve lacking in Ayios Dimitrios's heavily restored mosaics.