The Battle of Bathys Ryax was fought in 872 or 878 between the Byzantine Empire and the Paulicians. 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. The battle was a decisive Byzantine 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.