Coordinates: 43°48′56″N 22°54′55″E / 43.81556°N 22.91528°E
Ratiaria (or: Raetiaria, Retiaria, Reciaria, Razaria; Bulgarian: Рациария; Greek: Ραζαρία μητρόπολις; later named Colonia Ulpia Traiana Ratiaria) was a city founded by Moesi, a Daco-Thracian tribe, in 4th century BC, along the river Danube. The former Archdiocese was revived as Latin Catholic Metropolitan titular archbishopric. The city had a gold mine in the vicinity, which was exploited by the Thracians.
It is located 2 km west of present village Archar in Vidin Province, northwestern Bulgaria. The closest modern cities are Vidin (27 km. to the north west) and Lom (28 km. to the east).
Ratiaria was conquered by the Dacians of Burebista and later by Romans.
The earliest involvement of the Romans occurred in 75 BC, when Gaius Curio Scribonius Burbuleio, prefect of Macedonia, entered this territory to ward off Scordisci, the Dardani and Daci.