The tribe of Dacians was located north of the Danube River in southeastern Europe in what is today Romania and Moldova. At various times in their history, The Dacians, called Getae by the Greeks, expanded south of the Danube to the edge of the Balkan Mountains in what is now modern Bulgaria. The Dacians had a propensity for centralization which was rare for the peoples of the region and this trait made them a dangerous adversary for any power operating in the vicinity of the Danube.
During the first century AD, before Trajan, the Roman frontier in southeast Europe had its northern boundary at the Danube River stretching from Vienna all the way to the Black Sea. The Danube was fortified along its entire length with large forts, watchtowers, and auxiliary units assigned to reconnaissance, while two naval fleets, the Classis Pannonica and Classis Moesia, patrolled the river itself.