The Church of Saint Demetrius in Thessaloniki, Macedonia, Greece was originally built over a Roman bathhouse in the 4th century AD where Thessaloniki's patron saint was martyred by the Romans in 303 AD, 10 years before Christianity was legalized in the Roman empire through the Edict of Milan. The structure we see today (due to fire) was rebuilt in 629–634 AD during the Byzantine era. This remained a church until the end of the 15th century when the Ottomans converted it into a mosque and was use