Emperor Basil's reign was marked by the troublesome ongoing war with the heretical Paulicians, centered on Tephrike on the upper Euphrates, who rebelled, allied with the Arabs, and raided as far as Nicaea, sacking Ephesus. The Paulicians were a Christian sect which—persecuted by the Byzantine state—had established a separate principality at Tephrike on Byzantium's eastern border and collaborated with the Muslim emirates of the Thughur, the Abbasid Caliphate's borderlands, against the Empire. At the Battle of Bathys Ryax, the Byzantine led by Basil's general Christopher, won a decisive victory, resulting in the rout of the Paulician army and the death of its leader, Chrysocheir. This event destroyed the power of the Paulician state and removed a major threat to Byzantium, heralding the fall of Tephrike itself and the annexation of the Paulician principality shortly after.