A still greater disaster awaited the books of the Persians at the hand of the Moslem invader, when the Arabian horde swept over the hills and valleys of Persia like a simoon from the desert. Every tree and flower seemed to feel the withering touch of the barbarian, and the authority of the Korān was enforced with the logic of the sword. “Ye know your option, ye Christian dogs; the Korān, tribute, or the sword,” was the dictum of the conqueror wherever the Moslem flag was triumphant, and at last the Star and Crescent floated over the land of “the Lion and the Sun”—her nationality was humiliated and crushed, while her treasures of literature were again destroyed by a foreign foe. The kingdom of Persia now entered upon the long night of Mohammedan rule. Her sacred books were swept from the land, the Korān became the successor of the Zend- Avesta, and many of the Pārsīs went into voluntary exile, finding upon the shores of India that freedom which was denied them upon their native soil. Even the Persian tongue was placed under a ban, and Arabic became the legal language of court and council hall. The Persians were conquered, but not subdued; the national spirit still lived in their hearts, and in more than one instance the conquest was repeated—for, in the defence of their nationality and their faith, they rebelled in different portions of the country and fought desperately against the hated Arab. They were subjugated at last, and, to a certain extent, accepted even the religion of the invader, but the vitality of the Persian character was not destroyed. After a time, a few of the subordinate rulers, who were natives, rebelled against the tyranny of the Arabic tongue, and succeeded in establishing the Persian language to a great extent in its rightful domain. The national spirit again rallied, Persian poets were encouraged, traditions of the empire were once more collected, and the composition of a great national epic became possible. The Shāh Nāmah, which was written under royal patronage, has lived through the vicissitudes of more than eight hundred years, and is still the most popular Persian classic. Other centuries followed, bearing the names of distinguished poets and scholars, the cities of Bokhāra, Samarcānd and Bagdad became great literary centers, their colleges and libraries being celebrated throughout the East. But again the power of brute force was destined to sweep away the bulwarks of civilization, and Genghis Khān, the Tartar chief, came down like a mountain storm upon the fairest provinces of the Orient. The principal cities were pillaged and burned by the Tartar horde, colleges were destroyed, and the most valuable books in the libraries were thrown into the Tigris. These were times which tried the hearts of men, for more than two hundred thousand lives were sacrificed to the cruelty of the invading host. Scholars were driven to various places of refuge, and the science of letters received an almost fatal blow.