The saint’s name appears on 9 April, as a native of Sirmium, in Mart. Syr. and Mart. hier., in which he is called a deacon; they do not mention a martyr with this name honored at Thessalonica. After the destruction of Sirmium by Attila in 441, the saint’s cult was probably moved to Thessalonica where, in ca. 510–520, a basilica was built in his honor within the walls over older structures. There was no tomb with relics: a ciborium replaced the presence of the saint’s relics. The political situation influenced the growth of his legend: in 535 the seat of the prefecture of Illyricum was moved from Sirmium to Thessalonica. The legend turned the deacon into a soldier and proconsul who suffered under Maximian 306. In the 7th c., the collection of miracles edited by Archbishop John of Thessalonica calls him an intercessor and protector of the city against the Avars and Slavs. Demetrius is depicted at Rome in S. Maria Antiqua; icons frequently depict him as a cavalryman.
Cyril and Methodius brought his cult to Moravia and Pannonia, the Crusades to the West. The Greeks celebrate Demetrius 26 October; Florus inserts him in his martyrology on 8 October. BHG 496-547; BHL 2121-2127; BHO 248-251; BS 4, 556-565; LCI 6, 41-45; BBKL 1, 1255-1256; LMA 3, 686-689; E. Lucius, Die Anfänge des Heiligenkults in der christlichen Kirche, Tübingen 1904, 214-228; W. De Grüneisen, Sainte Marie Antique, Rome 1911, 522-523; P. Lemerle, Les plus anciens recueils de miracles de S. Démétrius et la pénétration des Slaves dans les Balkans, 1. Le texte, Paris 1979; C. Bakirtzis, Le culte de Saint Démétrius: Akten des XII. Internationalen Kongresses für Christliche Archäologie, Vatican City – Münster 1995, 58-68; E. Schurr, Die Ikonographie der Heiligen, Dettelbach 1997, 252-263; J.C. Skedros, Saint Demetrios of Thessaloniki. Civic Patron and Divine Protector, 4th-7th Centuries CE, Harrisburg 1999 with a tr. of BHG 496-497; D. Woods, Thessalonica’s Patron. Saint Demetrius or Emeterius?: HTR 93 2000 221-234; Ch. Bakirtzis, Pilgrimage to Thessalonike. The Tomb of St. Demetrios: DOP 56 2002 175-192.