The first Moslems were entirely ignorant of art and science, all their attention being devoted to the ordinances of the Koran, which they "carried in their breasts," and to the practice (_sunna_) of the Prophet. At that time the Arabs knew nothing of the way by which learning is taught, of the art of composing books, and of the means whereby knowledge is enregistered. Those, however, who could repeat the Koran and relate the Traditions of Muḥammad were called Readers (_qurrá_). This oral transmission continued until the reign of Hárún al-Rashíd, when the need of securing the Traditions against corruption or of preventing their total loss caused them to be set down in writing; and in order to distinguish the genuine Traditions from the spurious, every _isnád_ (chain of witnesses) was carefully scrutinised. Meanwhile the purity of the Arabic tongue had gradually become impaired: hence arose the science of grammar; and the rapid development of Law and Divinity brought it about that other sciences, _e.g._, logic and dialectic, were professionally cultivated in the great cities of the Muḥammadan Empire. The inhabitants of these cities were chiefly Persians, freedmen and tradesmen, who had been long accustomed to the arts of civilisation. Accordingly the most eminent of the early grammarians, traditionists, and scholastic theologians, as well as of those learned in the principles of Law and in the interpretation of the Koran, were Persians by race or education, and the saying of the Prophet was verified--"_If Knowledge were attached to the ends of the sky, some amongst the Persians would have reached it._" Amidst all this intellectual activity the Arabs, who had recently emerged from a nomadic life, found the exercise of military and administrative command too engrossing to give them leisure for literary avocations which have always been disdained by a ruling caste. They left such studies to the Persians and the mixed race (_al-muwalladún_), which sprang from intermarriage of the conquerors with the conquered. They did not entirely look down upon the men of learning but recognised their services--since after all it was Islam and the sciences connected with Islam that profited thereby.[508]