What applies to many of the early martyrs, also applies to Dimitrios: Historically reliable sources are lacking. From the different legends we get a rough outline.  He is said to have come from a consul's family and have been officer in the army. He dedicated himself to the preaching of the Gospel and was arrested, because he had particular success in Thessaloniki (Thessalonika). His Hagiograph Metaphrastes therefore calls him the "second apostle Paul".
Emperor Maximilian who was in the city at the time and met the arrested, had him incarcerated in the dungeons of the stadium in which gladiator fights were to take place. Nestor, a young man of the people who had killed his opponent Lyaios with one blow, signed up for the fight against his best gladiator. The enraged Emperor, on leaving the stadium, suddenly remembered Dimitrios, and had his soldiers kill him with their lances. According to other reports Nestor is said to have been a friend of Dimitrios, who had blessed him before the fight … (306 AD in Achaia) .
He represented the creating of a myth and was particularly revered in Thessaloniki. Through holy relics brought in by the crusaders, he became known in Western Europe and Western Germany too. As a crowned figure with shield and lance he was pictured on the Anno-Shrine at the end of the twelfth century.  He is one of the “Holy Knights” which are found in various arrangements.  In old “martyrologies” only one Dimitrios was known in Syria, however not in Thessaloniki).  The cross in the hand of the warrior underlines the symbolic aspect of his rank in the war: Demetrios is shown as martyr and fighter of the heavenly ruler.