In the dominions of the newly established Caliphs they were not only left in peace, but treated with especial honour.[85] The victorious Arabs were but a rude and uncivilized people, and the aid of the Jews in teaching them the arts and pleasures of a refined state of society was found alike useful and welcome. Their learning, their intelligence, their widespread knowledge of foreign lands, rendered them especially qualified for this office. Omar, the second Caliph, is related to have entrusted the coinage to a Jew, immediately after his accession to the throne. It was a subject with which, as might be expected, he had no acquaintance, nor was there any one among his principal officers who knew more of the matter. Similarly, if an embassy was to be despatched to a foreign sovereign, or a subsidy negotiated, the person selected for the office would in all likelihood be a Jew. When Abu Giafar imposed a heavy fine on the Christians, it was to Hebrew officials that the collection of the impost was committed; and even between sovereigns so potent as Charlemagne and the Caliph Haroun Alraschid, the envoy who was entrusted with the letters and presents was a Jew. In war they were no less necessary than in peace. The sums required for the equipment of a fleet or the victualling of an army were furnished from Hebrew coffers. Nor were their avocations limited to this. The Jews would accompany the march of the Mussulman armies, and—as their fathers had done in the instance of the Gothic and Hunnite invasions—purchase from the ignorant soldiery the plunder they had amassed, at a price which brought them an enormous profit,[86] or it might be a captive whose family or friends afterwards redeemed him at a price tenfold exceeding what they had given. We learn that at this time they almost entirely abandoned agriculture; partly because of the heavy tax laid on unbelievers, and partly because trade had become so much more profitable to them. They cultivated also astrology and medicine, and became everywhere the most successful professors of both sciences. In many, if not in most of the royal courts, the chief physicians and astrologers were Jews. Nor were they less successful in literature. In the East and West alike, their schools were crowded with students, and the names of their learned men of this era are held in reverence even to the present day.