About 17 km west from Burgas, in the mainland village of Debelt, are the ruins of the major city in the area in Roman times – Deultum.
The city was founded in the 1st Century AD during the reign of Emperor Vespasian as a colonia for veterans of Legio VIII Augusta.
In those times Deultum was connected to the Black Sea via its own port on a navigable lake, which was later filled with alluvium and became the Mandrensko Lake. In the 2nd Century the city flourished from trade and was fortified under Emperor Antoninus Pius. After the imperial capital had been moved to Byzantium, Deultum's military role grew and in the mid-4th Century a new fortification wall was built around it, this time including the neighbouring hill. It was this part of ancient Deultum which continued its life in the Middle Ages as an important fortress.
The most impressive remains of the ancient Deultum are the spacious baths, built in the 1st Century AD and enlarged and redecorated later. The city's ruins have produced plenty of interesting archaeological material, but by far the most memorable is the rare bronze portrait of Emperor Septimius Severus. The head, together with two hands also found in Deultum, used to belong to a life-size statue which adorned a spacious temple to the cult of the Roman emperors. Curiously, the statue is in its current condition after it was... blown up. It happened during an invasion when a particularly fierce fire destroyed the entire temple. As the statue was hollow, the air inside expanded with a bang, tearing the bronze emperor to pieces.