to consult the church, and he appears to have been surprised by the depth of the popular opposition he encountered". The controversy weakened the Byzantine Empire, and was a key factor in the schism between the Patriarch of Constantinople and the Bishop of Rome. The Umayyad Caliphate however was increasingly distracted by conflicts elsewhere, especially its confrontation with the Khazars, with whom Leo III had concluded an alliance, marrying his son and heir, Constantine V (r. 741–775) to the Khazar princess Tzitzak. Only in the late 730s did the Muslim raids again become a threat, but the great Byzantine victory at Akroinon and the turmoil of the Abbasid Revolution led to a pause in Arab attacks against the Empire. It also opened up the way for a more aggressive stance by Constantine V (r. 741–775), who in 741 attacked the major Arab base of Melitene, and continued scoring further victories. These successes were also interpreted by Leo III and his son Constantine as evidence of God's renewed favour, and strengthened the position of Iconoclasm within the Empire. Early Abbasids Unlike their Umayyad predecessors, the Abbasid caliphs did not pursue active expansion: in general terms, they were content with the territorial limits achieved, and whatever external campaigns they waged were retaliatory or preemptive, meant to preserve their frontier and impress Abbasid might upon their neighbours. At the same time, the campaigns against Byzantium in particular remained important for domestic consumption. The annual raids, which had almost lapsed in the turmoil following the Abbasid Revolution, were undertaken with renewed vigour from ca. 780 on, and were the only expeditions where the Caliph or his sons participated in person. As a symbol of the Caliph's ritual role as the leader of the Muslim community, they were closely paralleled in official propaganda by the leadership by Abbasid family members of the annual pilgrimage (hajj) to Mecca. In addition, the constant warfare on the Syrian marches was useful to the Abbasids as it provided employment for the Syrian and Iraqi military elites and the various volunteers (muṭṭawi‘a) who flocked to participate in the jihad. Wishing to emphasize his piety and role as the leader of the Muslim community, Caliph Harun al-Rashid (r. 786–809) in particular was the most energetic of the early Abbasid rulers in his pursuit of warfare against Byzantium: he established his seat at Raqqa close to the frontier, he complemented the thughur