Ancient Town Deultum (Деултум, Δεβελτός)

Deultum's origins date back to the Late Bronze Age, followed by a Thracian settlement in the Hallstatt period. In 70 AD, Emperor Vespasian founded a veteran colony here called Colonia Flavia Pacis Deultensium. Under Roman rule, Deultum developed into the second most important city in the province of Thrace and became a transport hub where the Via Militaris met the Via Pontica. Under Emperor Marcus Aurelius, the colony was surrounded by fortress walls. With the rise of Constantinople in the 4th century, Deultum was expanded into a fortress. In the early Middle Ages, it served as a border post between Bulgaria and Byzantium. In 812, the Bulgarian ruler Krum conquered the city, resettled its population, and had the Bulgarian-Byzantine border wall, the Erkesija, built. In the 13th century, the silting of Lake Mandra led to the decline of the port and possibly the end of the city after the Ottoman conquest.

The ruins of the ancient city of Deultum are located in the village of Debelt, which belongs to the Sredez district in the Burgas region of Bulgaria. The site is situated at an elevation of approximately 9 meters above sea level.