[6] The earliest written accounts of his life were compiled in the 9th century, although there are earlier images of him, and the 7th-century Miracles of Saint Demetrius collection.

Most historical scholars follow the hypothesis put forward by Bollandist Hippolyte Delehaye (1859–1941), that his veneration was transferred from Sirmium[9] when Thessaloniki replaced it as the main military base in the area in 441/442 AD.

After the demise of the Eleusinian Mysteries, Demeter's cult, in the 4th century, the Greek rural population had gradually transferred her rites and roles onto the Christian saint Demetrius.

Disputes between Bohemond I of Antioch and Alexios I Komnenos appear to have resulted in Demetrius being appropriated as patron saint of crusading.

[11] Most scholars still believe that for four centuries after his death, Demetrius had no physical relics, and in their place an unusual empty shrine called the "ciborium" was built inside Hagios Demetrios.

[15] Demetrius was initially depicted in icons and mosaics as a young man in patterned robes with the distinctive tablion of the senatorial class across his chest.

[16] Another Sinai icon, of the Crusader period and painted by a French artist working in the Holy Land in the second half of the 12th century, shows what then became the most common depiction.

According to a hagiographic legend, best known in Russia in the version retold by Dimitry of Rostov (1651–1709), Demetrius appeared in the camp of tsar Kaloyan of Bulgaria during his 1207 siege of Thessaloniki, piercing the king with a lance and so killing him.

This scene, known in Russian as Чудо о погибели царя Калояна ("the miracle of the destruction of tsar Kaloyan") became a popular element in the iconography of Demetrius.