The chronology and exact course of events are somewhat vague, but generally tradition puts Mu‘awiya’s decision to come out openly against ‘Ali only after the battle of the Camel. At first, we are told, he limited himself to impugning ‘Ali’s legitimacy, demanding that those who had killed ‘Uthman be handed over for punishment in accordance with the law of blood vengeance, and arousing among his Syrian Arab supporters fury at ‘Uthman’s murder. Although not the closest relative of the murdered caliph, Mu‘awiya was the Umayyad with the strongest power base, having governed Syria for about fifteen years and, furthermore, being free from suspicion of having benefited from ‘Uthman’s alleged nepotism since he owed his appointment in Syria to ‘Uthman’s predecessor, the venerable ‘Umar. At this time Mu‘awiya was not claiming the caliphate for himself, merely demanding vengeance for ‘Uthman and questioning ‘Ali’s right to rule. In the spring of 657 ‘Ali marched north from Kufa on campaign against Mu‘awiya and the latter, who had been attempting to wrest Egypt from ‘Ali’s governor, headed for Mesopotamia to meet him. The two met at Siffin, a site which has not been securely identified but which seems to have been in the vicinity of Raqqa but on the right bank of the Euphrates. It was late spring or early summer, and we are told that the armies faced each other for some time before fighting commenced. Then, according to the Muslim reports (contradicted by the Byzantine chronicler Theophanes), ‘Ali’s men were on the point of victory when there occurred an episode which has become famous. What happened is to some extent obscure but it is generally accepted that Mu‘awiya’s men raised copies or parts of the Koran on the ends of their spears and ‘Ali’s men, or the more pious among them, seeing this, forced ‘Ali to stop fighting and enter into negotiation with Mu‘awiya… [T]he arbitration does not appear to have had much importance for the further development of the Fitna, except insofar as ‘Ali had diminished his status as caliph by agreeing to take part in it. More important was the major split which occurred in the support for ‘Ali after the battle of Siffin. On the way back to Kufa, we are told, a large part of his army withdrew their allegiance to him and left his camp because they now repented of their appeal to him to stop the fighting and enter into discussions. They demanded that ‘Ali too should repent and withdraw from the arbitration. As a slogan signifying their opposition to the arbitration they adopted the formula, ‘arbitration (or judgement) belongs to God alone’ (la hukma illa li’llah), which is traditionally interpreted as a protest against the decision to appoint men (the two arbitrators) to decide what was fundamentally a religious matter and should therefore be left to God. These dissidents among the supporters of ‘Ali came to be known as ‘Kharijites’ (‘those who went out’ or ‘rebels’) and the slogan remained a badge of the movement long after the Fitna was over. For the Kharijites the immediate enemy now became ‘Ali, who had to be fought until he repented of his decision to accept the arbitration. This ‘Ali could not do, and from Siffin onwards he had to devote more time to his struggle against the Kharijites and less to that with Mu‘awiya. He achieved a major victory over the Kharijites at the battle of Nahrawan in Iraq (658), but this, by providing the movement with martyrs, merely intensified the hatred against him. After Siffin, therefore, we see a steady erosion of ‘Ali’s position: he seemed to have given grounds for the questioning of his legitimacy by agreeing to the arbitration…G. R. Hawting (1986). The First Dynasty of Islam: The Umayyad Caliphate AD 661-750, pp. 27-30.