During the siege of Constantinople, Heraclius formed an alliance with people Byzantine sources called the "Khazars", under Ziebel, now generally identified as the Western Turkic Khaganate of the Göktürks, led by Tong Yabghu, plying him with wondrous gifts and the promise of marriage to the porphyrogenita Eudoxia Epiphania. Earlier, in 568, the Turks under Istämi had turned to Byzantium when their relations with Iran soured over commerce issues. Istämi sent an embassy led by the Sogdian diplomat Maniah directly to Constantinople, which arrived in 568 and offered not only silk as a gift to Justin II, but also proposed an alliance against Sasanian Iran. Justin II agreed and sent an embassy to the Turkic Khaganate, ensuring the direct Chinese silk trade desired by the Sogdians.

In the East, in 625 CE, the Turks took advantage of the Sasanian weakness to occupy Bactria and Afghanistan as far as the Indus, and establish the Yabghus of Tokharistan. The Turks, based in the Caucasus, responded to the alliance by sending 40,000 of their men to ravage the Iranian Empire in 626, marking the start of the Third Perso-Turkic War. Joint Byzantine and Göktürk operations were then focused on besieging Tiflis, where the Byzantines used traction trebuchets to breach the walls, one of the first known uses by the Byzantines. Khosrow sent 1,000 cavalry under Shahraplakan to reinforce the city, but it nevertheless fell, probably in late 628.