But it was on the banks of the Zab, and not in the mosch of Cufa, that this important controversy was determined.

Every advantage appeared to be on the side of the white faction: the authority of established government; an army of a hundred and twenty thousand soldiers, against a sixth part of that number; and the presence and merit of the caliph Mervan, the fourteenth and last of the house of Ommiyah.

Before his accession to the throne, he had deserved, by his Georgian warfare, the honorable epithet of the ass of Mesopotamia; and he might have been ranked amongst the greatest princes, had not, says Abulfeda, the eternal order decreed that moment for the ruin of his family; a decree against which all human fortitude and prudence must struggle in vain.

The orders of Mervan were mistaken, or disobeyed: the return of his horse, from which he had dismounted on a necessary occasion, impressed the belief of his death; and the enthusiasm of the black squadrons was ably conducted by Abdallah, the uncle of his competitor.

After an irretrievable defeat, the caliph escaped to Mosul; but the colors of the Abbassides were displayed from the rampart; he suddenly repassed the Tigris, cast a melancholy look on his palace of Haran, crossed the Euphrates, abandoned the fortifications of Damascus, and, without halting in Palestine, pitched his last and fatal camp at Busir, on the banks of the Nile.