#ancient fortress

• Aegyssus — An ancient Geto-Dacian fortress, later recorded as a Roman border stronghold located on the right bank of the Danube, within the modern territory of Tulcea in Dobrogea, Romania. Founded according to legend by a Dacian chieftain named Carpyus, the city played a major strategic role in the Roman defensive system (Limes Moesiarum), described by the poet Ovid in his works from exile as an imposing fortification difficult to conquer due to its position on high cliffs.
• Arrubium — The ancient designation of a Roman castrum and fortified civil settlement situated in the province of Moesia Inferior, archaeologically located on the current territory of Măcin town in Tulcea County, Romania. The fortified site held an essential strategic role within the Danubian limes defensive network, securing fluvial traffic monitoring and the imperial border's protection against trans-Danubian migratory incursions.
• Axiopolis — An ancient Greco-Roman fortress and city, later fortified by the Byzantines, located in Dobruja on the right bank of the Danube, south of modern Cernavodă (opposite Hinog island). Initially founded in the 4th century BC by Lysimachus, king of Thrace, the settlement was structurally rebuilt by Emperor Constantine the Great. It served as a major strategic military and commercial hub, becoming an episcopal seat in the 6th century and a site of martyrdom for Saints Cyril, Quindeus, and Tassius.