How a nomadic alliance nearly toppled the Sassanid Empire
In the early 7th century, a desperate Byzantine Emperor forged an unlikely bond with the Western Turkic Khaganate. Driven by the need to protect Silk Road commerce, this massive cavalry force descended upon the Caucasus, shattering imperial strongholds and fundamentally altering the balance of power in the Near East.
By 627, the Byzantine Empire was in crisis. Following the 626 siege of Constantinople by a combined Avar and Sassanid force, Emperor Heraclius found himself politically isolated. Local Christian leaders in Transcaucasia were often alienated by the Orthodox Church, leaving Heraclius to seek allies elsewhere. He found a natural partner in Tong Yabghu Qaghan of the Western Turkic Khagante, who sought to secure the lucrative Chinese-Byzantine trade routes that Persian raids had recently disrupted.
The ensuing conflict saw a devastating invasion of the Caucasus. The Göktürks and their Khazar allies breached the Caspian Gates at Derbent, a stronghold once thought impregnable. The historian Movses Kagankatvatsi described the invaders as a 'scourge' that demolished walls and slaughtered inhabitants with little mercy. The Turkic heavy cavalry and Khazar archers overwhelmed the local Aghvanian militias, eventually pushing forces back toward the mountains and imposing heavy taxes on everything from gold extraction to river fishing.
The campaign reached a symbolic peak during the siege of Tbilisi. Heraclius and Tong Yabghu met under the walls of Narikala, where the Emperor even crowned the Khagan with his own diadem. While the Byzantine-Turkic forces eventually struggled with the prolonged siege, the momentum shifted southward. In late 627, Heraclius struck near the ruins of Nineveh, and by January, he was ravaging the environs of the Persian capital, Ctesiphon. This period of intense warfare demonstrated how nomadic mobility and Byzantine desperation could converge to dismantle established imperial hegemony.
Source: Perso-Turkic war of 627–629
