Haroun's crimes, however, consisted little in acts of persecution. The Persian Barmekides (the family of his first Vizier, surnamed Barmek) were regarded as protectors of Motazilites; [1075] and one of the sons, Jaafer, was even suspected of atheism, all three indeed being charged with it. [1076] Their destruction, on other grounds, does not seem to have altered the conditions for the thinkers; but Haroun's incompetent son Emin was a devotee and persecutor. His abler brother and conqueror Al Mamoun (813-833), on the other hand, directly favoured the Motazilites, partly on political grounds, to strengthen himself with the Persian party, but also on the ground of conviction. [1077] He even imprisoned some of the orthodox theologians who maintained that the Koran was not a created thing, though, like certain persecutors of other faiths, he had expressly declared himself in favour of persuasion as against coercion. [1078] In one case, following usage, he inflicted a cruel torture. "His fatal error," says a recent scholar, "was that he invoked the authority of the State in matters of the intellectual and religious life." [1079] Compared with others, certainly, he did not carry his coercion far, though, on being once publicly addressed as "Ameer of the Unbelievers," he caused the fanatic who said it to be put to death. [1080] In private he was wont to conduct meetings for discussion, attended by believers and unbelievers of every shade, at which the only restriction was that the appeal must be to reason, and never to the Koran. [1081] Concerning his personal bias, it is related that he had received from Kabul a book in old Persian, The Eternal Reason, which taught that reason is the only basis for religion, and that revelation cannot serve as a standing ground. [1082] The story is interesting, but enigmatic, the origin of the book being untraceable. Whatever were his views, his coercive policy against the orthodox extremists had the usual effect of stimulating reaction on that side, and preparing the ultimate triumph of orthodoxy. [1083] The fact remains, however, that Mamoun was of all the Khalifs the greatest promoter of science [1084] and culture; the chief encourager of the study and translation of Greek literature; [1085] and, despite his coercion of the theologians on the dogma of the eternity of the Koran, tolerant enough to put a Christian at the head of a college at Damascus, declaring that he chose him not for his religion but for his science. In the same spirit he permitted the free circulation of the apologetic treatise of the Armenian Christian Al Kindy, in which Islam and the Koran are freely criticized. As a ruler, too, he ranks among the best of his race for clemency, justice, and decency of life, although orthodox imputations were cast on his subordinates. His successors Motasim and Wathek were of the same cast of opinion, the latter being, however, fanatical on behalf of his rationalistic view of the Koran as a created thing.