sentences:  Tong Yabghu's empire fought with the Sassanids of Iran.In the early 620's the khagan's 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 khagan of the Khazars) campaigned with the Emperor Heraclius in the Caucasus against the Sassanid Persian Empire in 627–628.