​Here’s what the Balkans looked like in 535 CE just after emperor Justinian inaugurated Justiniana Prima, his new city in the middle of the Diocese of Dacia that acted as the centrepiece of his defensive system in the region.

Note the key cities on either side of the Danube, as well as the arrival of new peoples on the borders of the empire: the Antes, Sclaveni, and Bulgars.