religion. However, Manuel squandered his time and popularity in plundering the countryside, and eventually the Arab army managed to force him to embark for home. The situation was complicated by the violent opposition to Monothelitism by the clergy in the west and the related rebellion of the Exarch of Carthage, Gregory the Patrician. The latter fell in battle against the army of caliph Uthman, and the region remained a vassal state under the Caliphate until civil war broke out and imperial rule was again restored. Constans attempted to steer a middle line in the church dispute between Orthodoxy and Monothelitism by refusing to persecute either and prohibiting further discussion of the natures of Jesus Christ by decree in 648 (the Type of Constans). Naturally, this live-and-let-live compromise satisfied few passionate participants in the dispute. Meanwhile, the advance of the Rashidun Caliphate continued unabated. In 647 they entered Armenia and Cappadocia and sacked Caesarea Mazaca. In the same year, they raided Africa and killed Gregory. In 648, the Arabs raided into Phrygia, and in 649 they launched their first maritime expedition against Crete. A major Arab offensive into Cilicia and Isauria in 650–651 forced the Emperor to enter into negotiations with Caliph Uthman's governor of Syria, Mu'awiya I (), who later reigned as the first Umayyad caliph. The truce that followed allowed a short respite and made it possible for Constans to hold on to the western portions of Armenia. In 654, however, Mu'awiya renewed his raids by sea, plundering Rhodes. Constans led a fleet to attack the Muslims at Phoinike (off Lycia) in 655 at the Battle of the Masts, but he was defeated: 500 Byzantine ships were destroyed in the battle, and the Emperor himself was almost killed. The sea battle was so devastating that the emperor escaped only by trading clothes with one of his men. Before the battle, chronicler Theophanes the Confessor says, the Emperor dreamed of being at Thessalonika; this dream predicted his defeat against the Arabs because the word Thessalonika is similar to the sentence "thes allo niken", which means "gave victory to another (the enemy)". Caliph Uthman was preparing to attack Constantinople, but he did not carry out the plan, as the first Fitna broke out in 656. In 658, with the eastern frontier under less pressure, Constans defeated the Slavs in the Balkans, temporarily reasserting some notion of Byzantine rule over them and