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. Background The Paulicians were a Christian sect whose precise origins and beliefs are somewhat obscure: Byzantine sources portray them as dualists, while Armenian sources maintain that they were an adoptionist sect. The Paulicians were fiercely iconoclastic, adhered to a very distinct Christology, and rejected the authority and practices of the official Byzantine Church, following their own leaders. Consequently, they were persecuted by the Byzantine state as early as 813, despite the emperors' official support for iconoclasm. After the definitive end of Byzantine Iconoclasm in 843, that persecution was intensified: in an attempt, unique in Byzantine history, to eradicate an entire "heretical" sect, orders were sent out to kill anyone who would not recant. According to the chroniclers, up to 100,000 Paulicians were massacred, while the remnants fled from their strongholds in east-central Anatolia, and found refuge among the Empire's Muslim enemies, the Arab emirates of the Thughur, the Arab–Byzantine frontier zone along the Taurus–Antitaurus mountain ranges. With support from the emir of Melitene, Umar al-Aqta, the Paulician leader Karbeas founded a separate principality at Tephrike, and for the next decades, the Paulicians campaigned alongside the Arabs against Byzantium. The Arabs and Paulicians suffered a critical blow in 863 with the defeat and death of Umar at the Battle of Lalakaon and the death of Karbeas in the same year, but under their new leader, Chrysocheir, the Paulicians resumed their raids deep into Byzantine Anatolia, raiding as far as Nicaea and sacking Ephesus in 869/970. The new Byzantine emperor, Basil I the Macedonian (), sent an embassy for negotiations to Tephrike. After the talks failed, Basil led a campaign against the Paulician state in the spring of 871, but was defeated and only narrowly managed to escape himself. Battle Encouraged by this success,