But the true protector and father of Arabic literature was Al Mamoun, the son of Haroun al Raschid (813-833), who rendered Bagdad the centre of literature. He invited to his court from every part of the world all the learned men with whose existence he was acquainted, and he retained them by rewards, honors, and distinctions of every kind. He exacted, as the most precious tribute from the conquered provinces, all the important books and literary relics that could be discovered. Hundreds of camels might be seen entering Bagdad, loaded with nothing but manuscripts and papers, and those most proper for instruction were translated into Arabic. Instructors, translators, and commentators formed the court of Al Mamoun, which appeared to be rather a learned academy, than the seat of government in a warlike empire. The Caliph himself was much attached to the study of mathematics, which he pursued with brilliant success. He conceived the grand design of measuring the earth, which was accomplished by his mathematicians, at his own expense. Not less generous than enlightened, Al Mamoun, when he pardoned one of his relatives who had revolted against him, exclaimed, "If it were known what pleasure I experience in granting pardon, all who have offended against me would come and confess their crimes." The progress of the Arabians in science was proportioned to the zeal of the sovereign. In every town of the empire schools, colleges, and academies were established. Bagdad was the capital of letters as well as of the Caliphs, but Bassora and Cufa almost equaled that city in reputation, and in the number of celebrated poems and treatises that they produced. Balkh, Ispahan, and Samarcand were equally the homes of science. Cairo contained a great number of colleges; in the towns of Fez and Morocco the most magnificent buildings were appropriated to the purposes of instruction, and in their rich libraries were preserved those precious volumes which had been lost in other places.