The western border of Byzantine Pannonia stretched approximately to the estuary or river Drina into Sava.

In the middle of the 5th century, the territory of former Roman Pannonia was ceded to the Huns by Theodosius II, and after the death of Attila it successively passed (entirely or partially) into the hands of the Ostrogoths, Lombards and Gepids.

The Lombard–Gepid War (567) ended with a Lombard-Avar victory and annihilation of Gepids, while Sirmium was retaken by the Byzantine Empire.

The city of Sirmium was finally conquered by the Avars in 582, thus marking end of Roman control of Pannonia since Classical Antiquity.

The Byzantine Empire re-established control over Pannonia in the 11th century, leading to the creation of the Theme of Sirmium to administer the region, but not lasting long.