When his father died, the Roman emperor Maximian ordered him to chase and kill the Christians of Thessaloniki. Dimitrios refused to do so and revealed his faith. He was asked to change his religious beliefs but refused once again and expressed his disgust for idolatry. Therefore, he was put to prison, was tortured and died for his God. Before he died, he donated all his wealth to the poor. His bravery and sacrifice made him an orthodox saint.
When the emperor Constantine the Great ended the prosecution of the Christians (324 A.D.) and made Christianity the official religion of the Byzantine Empire, people built a small church on the place of the martyrdom of Agios Dimitrios, close to the Roman baths. His grave was said to be miraculous and thousands of pilgrims were coming every year to pay their honors.
In 413 AD, a bigger three-aisled basilica was founded by the eparch Leontios, which was burnt down two centuries later, in 634 A.D. Shortly afterwards, an even bigger five-isled basilica was built, which remains till today and constitutes the largest church of Greece. In 1493, during the Turkish occupation, the church was converted into a mosque and in 1912, when the city was liberated, it became a Christian church again. In 1917, it was once again destroyed by a fire and rebuilt according to the original plans. It started to function again in 1949.
Agios Dimitrios became the patron saint of the city in 1912, during the First Balkan War, when the Greek army entered the city of Thessaloniki on his name day (October 26th) and delivered the city from the Turks. Today, his memory is celebrated every year, along with the deliberation of the city, with a big parade and a glorious Mass.