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In page Battle of Nineveh (627):

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While the Siege of Constantinople was taking place, Heraclius allied with what Byzantine sources called the Khazars under Ziebel, who are identified with the Western Turkic Khaganate of the Göktürks led by Tong Yabghu,[2] plying him with wondrous gifts and a promise of the reward of the porphyrogenita Eudoxia Epiphania. The Caucasus-based Turks responded by sending 40,000 of their men to ravage the Persian Empire in 626 to start the Third Perso-Turkic War.[3] Joint Byzantine and Göktürk operations were focused on besieging Tiflis.[4]