How a nomadic empire nearly dismantled Byzantium through a coordinated siege with Persian forces
The Avar Khaganate, a nomadic power in the Carpathian Basin, spent decades terrorizing the Byzantine Empire. By leveraging the technical skills of subject peoples and exploiting Byzantine distractions in the East, they pushed the empire to the brink before a failed, high-stakes siege of Constantinople triggered their ultimate collapse.
The Avar–Byzantine wars began in 568 after the Avars arrived in Pannonia, fleeing the First Turkic Khaganate. By seizing the lands of the Gepids and Lombards, they established a new Khaganate and immediately targeted the strategic city of Sirmium. For decades, the Avars exploited the Byzantine Empire’s preoccupation with the Sassanid Empire, raiding the Balkans with little resistance. When the Byzantines were distracted by the Byzantine–Sasanian War of 572–591, the Avars captured Sirmium around 581 or 582, subsequently demanding 100,000 gold solidi annually.
Avar military success relied heavily on subject peoples like the Slavs, who provided essential engineering expertise for siege warfare, including the construction of boats and bridges. The conflict shifted significantly in 591 when Emperor Maurice concluded a peace treaty with the Persians, allowing him to refocus on the Balkans. Byzantine forces, led by generals like Priscus, eventually pushed back, inflicting a major defeat on the Avars in their own territory during the 599 Battles of Viminacium. Despite these setbacks, the Avars remained a potent threat, especially as the Byzantines faced renewed Persian pressure under Emperor Heraclius.
The climax of the conflict occurred in 626, when the Avar Khagan coordinated a massive assault on Constantinople with the Persian king Khosrau II. While the Persians attacked from the Asiatic side, the Avars besieged the land walls. However, the Byzantine navy prevented the two forces from uniting, and the defenders repelled the Avar assaults. Following this failure, the Avar Khaganate rapidly disintegrated due to internal power struggles and tribal uprisings. Their power was further eroded by the Bulgars around 680, and the remaining rump state was finally conquered by Charlemagne between 790 and 803.
Source: Avar–Byzantine wars
