The Balkans were conquered and absorbed during classical antiquity into the territory of the Roman Empire. The regions and independent kingdoms of Thrace, Macedonia, Illyria and Dacia became Roman provinces. The province of Dacia was Rome's only foothold north of the Danube river.
Beginning in the 3rd century AD, Rome's frontiers in the Balkans were weakened because of political and economic disorders within the Empire. Though the situation had stabilized temporarily by the time of Constantine, waves of non-Roman peoples, most prominently the Visigoths, Ostrogoths and Huns, began to cross into the territory, first (in the case of the Visigoths) as refugees with imperial permission to take shelter from their foes the Huns, then later as invaders.
Turning on their hosts after decades of servitude and simmering hostility, Visigoths under Fritigern eventually conquered and laid waste the entire Balkan region before moving westward to invade Italy itself. By the end of the Empire the region had become a conduit for invaders to move westward, as well as the scene of treaties and complex political maneuvers by Romans, Goths and Huns, all seeking the best advantage for their peoples amid the shifting and disorderly final decades of Roman imperial power.
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