Between roughly 580 and 630 the Roman Balkan provinces ceased to function as an imperial space. Avar and Slavic raiding, the collapse of the Danube frontier after 602, and the withdrawal of field armies to the eastern front left the interior open to permanent settlement by Slavic-speaking groups, while surviving provincial populations concentrated in coastal cities, offshore islands and mountain refuges. Byzantine writers describe sacked cities, mass captive-taking and depopulation; archaeology shows the abandonment of Danubian forts and a break in urban life across the interior. The scale is unquantifiable: the chronicles give no reliable totals, and modern scholarship is divided between models of large-scale folk migration and models in which a smaller intrusive population catalysed a change of identity among people already there. The episode is included because the collapse of imperial control was accompanied by documented forcible movement of populations, not because a mass expulsion can be demonstrated.
Avar khaganate armies and Slavic groups raided, occupied and settled the Roman Balkan provinces while imperial administration and much of the provincial population withdrew to coastal cities and fortified sites
No defensible denominator exists. The late Roman Balkans have no surviving register, and any figure for 580 would have to reckon with the Justinianic plague of 541 onwards, whose demographic effect is itself one of the most contested questions in late antique history — estimates of mortality run from a few per cent to a third. McEvedy and Jones and other atlas-scale reconstructions give the peninsula figures in the low millions, but these are extrapolations from later medieval data rather than evidence for the sixth century.
No usable figures. Byzantine sources describe massacres and enslavement during raids but give no totals, and there is no demographic reconstruction that can separate deaths from flight, captivity or the ordinary mortality of a disrupted period.
The destruction and abandonment of Danubian forts and Balkan towns is documented archaeologically and in the Miracles of St Demetrius and Theophylact Simocatta; other forms alleged in the chronicles cannot be tied to specific documented episodes.
Macedonia, Serbia, Greece, Bulgaria