 Taking advantage of the Abbasids'preoccupation with the suppression of the Khurramite rebellion, the Byzantine emperor Theophilos had launched a number of attacks on the Muslim frontier zone in the early 830s, and scored a few successes. His forces were also bolstered by some 14,000 Khurramites who under their leader, Nasr, fled into the Empire, became baptized and enrolled into the Byzantine army under the command of Nasr, better known by his Christian name of Theophobos. In 837, Theophilos, urged by the increasingly hard-pressed Babak, launched a major campaign into the Muslim frontier lands, with an army reportedly numbering over 70,000 men, whom he led in an almost unopposed invasion around the upper Euphrates. The Byzantines took the towns of Zibatra (Sozopetra) and Arsamosata, ravaged and plundered the countryside, extracted ransom from Malatya and other cities in exchange for not attacking them, and defeated a number of smaller Arab forces. As refugees began arriving at Samarra, the caliphal court was outraged by the brutality and brazenness of the raids: not only had the Byzantines acted in open collusion with the Khurramites, but during the sack of Zibatra all male prisoners were executed and the rest sold into slavery, and some captive women were raped by Theophilos' Khurramites.
