Avar–Byzantine wars participant Avar Khaganate
Background
The Avars arrived in the Carpathian Basin in 568, fleeing from the First Turkic Khaganate. They quickly entered into an alliance with the Lombards to seize the land of the Gepids. However, during this process, the Lombards retreated to Italy, allowing the Avars to take both the lands of the Gepids and the former lands of the Lombards for themselves, creating the Avar Khaganate. The Avars then claimed all former territory of both as their own territory. This included Sirmium, which had been recently reconquered by the Byzantines from the Gepids, and would serve as the first cause of conflict between the Avars and the Byzantines.The Avars were heavily dependent upon the skills and labor of their subject peoples for both siege warfare and logistics. Subject peoples, such as the early Slavs and the Huns, had long traditions of engineering and craftsmanship, such as the building of boats and bridges, and the use of rams, tortoise formations, and artillery in sieges. In every documented use of siege engines by the Avars, the Avars depended upon subject peoples who had knowledge of them, usually the Sabirs, Kutrigurs, or Slavs. Avar military tactics also relied upon speed and shock.