The downfall of the Umayyads was hastened by the perfidy and selfishness of the Arabs on whom they relied: the old feud between Muḍar and Yemen broke out afresh, and while the Northern group remained loyal to the dynasty, those of Yemenite stock more or less openly threw in their lot with the Revolution. We need not attempt to trace the course of the unequal contest. Everywhere the Arabs, disheartened and divided, fell an easy prey to their adversaries, and all was lost when Marwán, the last Umayyad Caliph, sustained a crushing defeat on the River Záb in Babylonia (January, A.D. 750). Meanwhile Abu ’l-‘Abbás, the head of the rival House, had already received homage as Caliph (November, 749 A.D.). In the inaugural address which he delivered in the great Mosque of Kúfa, he called himself _al-Saffáḥ_, _i.e._, 'the Blood-shedder,'[478] and this title has deservedly stuck to him, though it might have been assumed with no less justice by his brother Mansúr and other members of his family. All Umayyads were remorselessly hunted down and massacred in cold blood--even those who surrendered only on the strength of the most solemn pledges that they had nothing to fear. A small remnant made their escape, or managed to find shelter until the storm of fury and vengeance, which spared neither the dead nor the living,[479] had blown over. One stripling, named ‘Abdu ’l-Raḥmán, fled to North Africa, and after meeting with many perilous adventures founded a new Umayyad dynasty in Spain. CHAPTER VI THE CALIPHS OF BAGHDÁD The annals of the ‘Abbásid dynasty from the accession of Saffáḥ (A.D. 749) to the death of Musta‘ṣim, and the destruction of Baghdád by the Mongols (A.D. 1258) make a round sum of five centuries. I propose to sketch the history of this long period in three chapters, of which the first will offer a general view of the more important literary and political developments so far as is possible in the limited space at my command; the second will be devoted to the great poets, scholars, historians, philosophers, and scientists who flourished in this, the Golden Age of Muḥammadan literature; while in the third some account will be given of the chief religious movements and of the trend of religious thought. [Sidenote: Political results of the Revolution.]