The present-day Church of Saint Demetrius stands above part of an ancient Roman bath complex. According to tradition, this was where the saint was imprisoned and martyred. The earliest Christian place of worship at the site dates to the first centuries following his martyrdom, while a large basilica was erected during the fifth century, eventually becoming one of the Byzantine Empire’s most important pilgrimage destinations. The present five-aisled basilica preserves exceptional architectural and artistic features. Particularly valuable are its early Christian and Byzantine mosaics, depicting Saint Demetrius alongside members of the clergy, officials, and worshippers. These artworks are not merely expressions of religious devotion but also invaluable evidence of the art and society of Byzantine Thessaloniki. Beneath the church lies the famous Crypt of Saint Demetrius, an underground archaeological site preserving remains of the Roman baths and later Christian structures. According to ecclesiastical tradition, the saint was imprisoned and martyred here. During the Byzantine period, the space was adapted for religious worship, incorporating reservoirs, marble architectural elements, and other features associated with his veneration. The title “Myrrh-Streamer” derives from the tradition that fragrant myrrh flowed from the saint’s tomb, which believers regarded as a source of blessing and healing. The crypt, rediscovered following the devastating fire of 1917, now serves as an archaeological museum displaying sculptures, architectural fragments, and other discoveries from the monument’s long history. Saint Demetrius was not simply an object of religious devotion but also a symbol of Thessaloniki’s collective identity. The famous Miracles of Saint Demetrius, texts of considerable historical importance for the early Byzantine period, reflect the inhabitants’ belief that their patron saint protected the city from sieges and enemy invasions. These accounts are also valuable historical sources for understanding Thessaloniki and its relationship with the peoples of the Balkans. The saint’s association with the city’s historical journey acquired new significance on October 26, 1912, when Thessaloniki came under Greek control during the First Balkan War, on the very day of his feast. This coincidence was interpreted by the faithful as a special blessing, establishing October 26 as a day of double celebration: the commemoration of the patron saint and the anniversary of the city’s liberation. Throughout its history, the church suffered repeated destruction and reconstruction. During the Ottoman period, it was converted into a mosque, while after Thessaloniki’s liberation, it was restored to Christian worship. The devastating fire of 1917 caused extensive damage, destroying much of the historic basilica. A lengthy restoration program followed, completed in 1948, allowing the church to recover its historic appearance. In 1988, the Church of Saint Demetrius was inscribed on the UNESCO World Heritage List as part of the Paleochristian and Byzantine Monuments of Thessaloniki. Today, approximately seventeen centuries after the period traditionally associated with the saint’s martyrdom, the basilica remains a living center of Orthodox worship, an archaeological treasure, and one of the most enduring symbols of the city’s historical identity.