Then, there was a reaction back again to the ‘Orthodox’ faith; and now, all who questioned the eternity of the Corân, who ventured to magnify the claims of Aly, or to detract from those of his predecessors in the Caliphate--Abu Bekr, Omar, Othmân--became in their turn the objects of unrelenting persecution. In one important respect, however, the Motázilite Caliphs (and we might say the Shîya sect in general) have excelled the Orthodox; they are especially distinguished by greater forbearance towards the professors of other creeds. With the return of orthodoxy the reign of intolerance revived; and against both Jews and Christians, the so-called ‘Ordinances of Omar’ were enforced by an Orthodox court with new and degrading penalties.[610] [Sidenote: Golden Age of literature at Baghdad.] The reigns of Al Mâmûn and his immediate successors were the palmy days of Moslem learning. At the court of Baghdad there were munificently entertained, philosophers, physicians, and men of letters. Amongst them were many Jews and Christians, versed at once in the Arabic tongue, and in the language and literature of Greece. The monasteries of Syria, Asia Minor, and the Levant, were ransacked for manuscripts of the Greek philosophers, historians, and geometricians. These, with vast labour and erudition, were translated into the Arabic; and thus the learning of the West was made accessible to the Moslem world. Nor were their efforts confined to the reproduction of ancient works, but in some directions extended also to original research. An observatory, reared on the plain of Tadmor, furnished materials for the successful study of astronomy and geometry. In other walks of literature, we have books of travel and history, and, above all, of medicine; while much attention was paid to the less practical, but more popular, branches of astrology and alchemy. It was through the labours of these learned men that the nations of Europe, then shrouded in the darkness of the Middle Ages, became again acquainted with their own proper, but unused and forgotten, patrimony of Grecian science and philosophy. [Sidenote: Introduction of mercenaries and fall of the Caliphate.]