Following the First Siege of Constantinople by the Avars and Persians, the beleaguered Byzantine Emperor Heraclius found himself politically isolated. He could not rely on the Christian Armenian potentates of Transcaucasia, since they were branded as heretics by the Orthodox Church, and even the king of Iberia preferred to befriend the religiously tolerant Persians. Against this dismal background, he found a natural ally in Tong Yabghu. Earlier in 568, the Turks under Istämi had turned to Byzantium when their relations with Persia soured over commerce issues.