The Battles of Viminacium were a series of three battles fought against the Avars by the East Roman (Byzantine) Empire. They were decisive Roman successes, which were followed by an invasion of Pannonia.

In summer 599, the East Roman Emperor Maurice sent his generals Priscus and Comentiolus to the Danube front against the Avars. The generals joined their forces at Singidunum and advanced together down the river to Viminacium. The Avar khagan Bayan I meanwhile - learning that the Romans had determined to violate the peace - crossed the Danube at Viminacium and invaded Moesia Prima, while he entrusted a large force to four of his sons, who were directed to guard the river and prevent the Romans from crossing over to the left bank. In spite of the presence of the Avar army, however, the Byzantine army crossed on rafts and pitched a camp on the left side, while the two commanders sojourned in the town of Viminacium, which stood on an island in the river. Here Comentiolus is said to have fallen ill or to have mutilated himself so as to be incapable of further action; Thus Priscus assumed command over both armies.

A battle was fought which cost the East Romans only three hundred men, while the Avars lost four thousands. This engagement was followed by two other great battles in the next ten days, in which the strategy of Priscus and the tactics of the Roman army were brilliantly successful. Priscus subsequently pursued the fleeing khagan and invaded the Avar homeland in Pannonia, where he won another series of battles on the banks of the River Tisza, deciding the war for the Romans and ending, for a time, the Avar and Slavic incursions across the Danube.