The Arabs of that period knew how to conquer and to hold fast what they had won; for organisation they had less aptitude. Wherever they could they left administration, and taxation more especially, as they found it. At first the register of taxes was kept in Greek in the former dominions of Rome, and in Persian in those of Persia; and not until after more than half a century did the Arabic language become predominant in official book-keeping. The Omayyads had gained the mastery by the loyalty of the Arabs of Syria; they were tied to Syria, and the great tracts of territory to the east were hard to rule from thence. Moreover the Moslems of Babylonia, in many respects a more important province, were on the whole hostile to them. And, what was worse, the old lack of discipline among the Arabs had manifested itself strongly in a new form. Instead of small clans being at feud with one another, as had usually been the case in former days, they had ranged themselves in large and mutually hostile groups. One of these was composed of the Arabs of Yemen (real or reputed), two others of the tribes which claimed descent from Ishmael, the Mudhar and Rabia. If a caliph or a caliph’s vicegerent sided with the Yemen he had the Mudhar against him; if he favoured the Rabia the Mudhar were likewise hostile, etc. In the remoter provinces the hostile Arabs sometimes waged regular wars with one another on their own account. To add to this, there were risings of fanatics of various kinds. None but the ablest of the Omayyads (and on the whole they were an able dynasty) could maintain even tolerable order in the vast empire which extended its borders farther and farther when once the civil wars were over. The brief reign of a weakling or a libertine was enough to spoil everything. The purely Arab empire lacked the elements of stability. Meanwhile, however, great masses of the conquered peoples had gone over to Islam. Temporal advantages on the one hand, and on the other the suitability of this coarse-grained religion to the Semites, and probably to the less educated Egyptians too, led steadily to the abandonment of a Christianity which in these parts was but little superior to Islam. But in Iran also the new religion soon made great advances on its own merits, though in some places (it must be admitted) very much at the expense of the purity of its pristine character. The national pride of the Arabs could not endure the practical application of the theoretical precept of Islam that all believers should be on an absolutely equal footing. The new converts remained Moslems of the second class, and, in certain districts at least, they felt the distinction bitterly. Even at the time of the second great civil war these so-called “clients” (_mawali_) had on one occasion played a prominent part, though only as the tools of an ambitious Arab.