Tong Yabghu's empire fought with the
Sassanids of
Iran. In the early 620's his nephew
Böri Shad led a series of raids across the
Caucasus Mountains into
Persian territory. Many scholars have identified Tong Yabghu as the
Ziebel mentioned in
Byzantine sources as having (as qaghan of the
Khazars) campaigned with the Emperor
Heraclius in the
Caucasus against the Sassanid Persian Empire in 627 and 628. However, the latest research on this topic proves that this is incorrect: if Tong indeed died in 628, Ziebel is to be identified with Sipi qaghan, Tong Yabghu's uncle, who murdered him and rose briefly to the throne. Sipi was by then pronounced Zibil and he was a small qaghan in charge of the western part of Tong Yabghu's empire, exactly as Ziebel was according to the Byzantine sources. Ziebel is described as the brother of Tong in the Byzantine sources, and as his uncle in the Chinese sources, a discrepancy which long precluded the identification. However uncle and elder brother is the same word in ancient Turkish,
äçi, and the Chinese sources could not render this double meaning with their very precise system of kinship names. Prior to this some scholars, including Chavannes, Uchida, Gao and Xue Zhongzeng had argued that Tong Yabghu could not be positively identified with Ziebel (or any Khazar ruler) and may actually have died as early as 626. They pointed to discrepancies in the dates between Byzantine and Chinese sources and argued that definitively conflating Ziebel with Tong Yabghu was an exaggeration of the extant evidence. stretched between the Caspian seashore and the Caucasus for forty kilometers; they are still in existence. ==Governance==