In the year 732, exactly one hundred years after the death of the great Prophet, the Franks, under their renowned chieftain, Charles, and their allies met the Moslems upon the plains of Tours in the centre of Gaul, and committed to the issue of a single battle the fate of Christendom and the future course of history. The desperate valor displayed by the warriors of both armies was worthy of the prize at stake. Abderrahman, the Mohammedan leader, fell in the thick of the fight, and night saw the complete discomfiture of the Moslem hordes. The loss that the sturdy blows of the Germans had inflicted upon them was enormous, the accounts of that age swelling the number killed to the impossible figures of 375,000. The disaster at all events was too overwhelming to permit the Saracens ever to recover from the blow, and they soon retreated behind the Pyrenees. The young civilization of Europe was thus delivered from an appalling danger, such as had not threatened it since the fearful days of Attila and the Huns. The heroic Duke Charles who had led the warriors of Christendom to the glorious victory was given the surname _Martel_, the "Hammer," in commemoration of the mighty blows of his huge battle-axe. CHANGES IN THE CALIPHATE.--During the century of conquests we have traced, there were many changes in the caliphate. Abubekr was followed by Omar (634-644), Othman (644-655), and Ali (655-661), all of whom fell by the hands of assassins, for from the very first dissensions were rife among the followers of the Prophet. Ali was the last of the four so-called "Orthodox Caliphs," all of whom were relatives or companions of the Prophet. Moawiyah, a usurper, was now recognized as Caliph (661). He succeeded in making the office hereditary, instead of elective, as it hitherto had been, and thus established what is known as the dynasty of the Ommiades [Footnote: So called from Ommaya, an ancestor of Moawiyah.], the rulers of which family for nearly a century issued their commands from the city of Damascus. The house of the Ommiades was overthrown by the adherents of the house of Ali, who established a new dynasty (750), known as that of the Abbassides, so called from Abbas, an uncle of Mohammed. The new family, soon after coming to power, established the seat of the royal residence on the lower Tigris, and upon the banks of that river founded the renowned city of Bagdad, which was destined to remain the abode of the Abbasside Caliphs for a period of five hundred years,--until the subversion of the house by the Tartars of the North.