Seeing that Muâvia was hopelessly alienated, Aly resolved no longer to delay the attack upon Syria, and he proclaimed an expedition accordingly. At first the people were slack in answering the call. But after a time, the Caliph succeeded in gathering together from Bussorah, Medâin, and Kûfa, an imposing force of 50,000 men. His plan was to march first by Upper Mesopotamia, and so to invade Syria from the north. A detachment was sent as an advance-guard up the western bank of the Euphrates, but meeting with active opposition there, it was forced to cross back again into Mesopotamia. Aly himself, with the main body, marched across the plain of Dura to Medâin, and thence up the Tigris. Then turning, short of Mosul, towards the west, he crossed the great desert of Mesopotamia, and, outstripping his advanced column, reached the Euphrates in its upper course at Ricca.[527] An unfriendly population lined the banks of the river; and it was not without sanguinary threats that Ashtar forced them to construct a bridge. The army crossed near Ricca; and then marching some little distance along the right bank, westward, in the direction of Aleppo, they met the Syrian outposts at Sûr.[528] [Sidenote: Muâvia, advancing, meets Aly, on field of Siffîn.] On learning Aly’s preparations, Muâvia lost no time in marshalling his forces, which greatly outnumbered the enemy, and, having no desert to cross, were soon to the front. Amru was in command, having his two sons, and his freedman Werdân, as lieutenants.[529] Aly, desirous of averting bloodshed, had given orders that, as soon as his troops came upon the enemy, they should halt, and, confining themselves to the defensive, avoid precipitating hostilities before opportunity had been given for friendly overture. The vanguards of the two armies spent the first few days in skirmishing. Ashtar challenged the Syrian officer to single combat; but the challenge was declined, and Ashtar told that, having imbrued his hands in the blood of the late Caliph, he could not claim the privileges of honourable warfare. When the main armies came in sight of each other, Aly found Muâvia so encamped as to cut him off from the river, and reduce his army to straits for water. He therefore brought on an engagement, in which Muâvia was forced to change his ground, and occupy the ill-starred field of Siffîn.[530a] Some days of inaction followed; after which Aly sent three of his chief men to demand that, for the good of the commonwealth, Muâvia should tender his allegiance. No mention is made of any offer (though perhaps it may be presumed) on the part of Aly to confirm Muâvia, in case of his submission, in the government of Syria. A scene ensued of fruitless recrimination. On the one hand, Muâvia demanded that the murderers of Othmân should be brought to justice; on the other, the demand was stigmatised as a mere cat’s-paw covering ambitious designs upon the Caliphate. This was resented as a base calumny by Muâvia. ‘Begone,