In order to follow the course of the spread of Islam eastward into Central Asia, we must retrace our steps to the period of the first Arab conquests. By the middle of the seventh century, the great dynasty of the Sāsānids had fallen, and the vast empire of Persia that for four centuries had withstood the might of Rome and Byzantium, now became the heritage of the Muslims. When the armies of the state had been routed, the mass of the people offered little resistance; the reigns of the last representatives of the Sāsānid dynasty had been marked by terrible anarchy, and the sympathies of the people had been further alienated from their rulers on account of the support they gave to the persecuting policy of the state religion of Zoroastrianism. The Zoroastrian priests had acquired an enormous influence in the state; they were well-nigh all-powerful in the councils of the king and arrogated to themselves a very large share in the civil administration. They took advantage of their position to persecute all those religious bodies—(and they were many)—that dissented from them. Besides the numerous adherents of older forms of the Persian religion, there were Christians, Jews, Sabæans and numerous sects in which the speculations of Gnostics, Manichæans and Buddhists found expression. In all of these, persecution had stirred up feelings of bitter hatred against the established religion and the dynasty that supported its oppressions, and so caused the Arab conquest to appear in the light of a deliverance. [687] The followers of all these varied forms of faith could breathe again under a rule that granted them religious freedom and exemption from military service, on payment of a light tribute. For the Muslim law granted toleration and the right of paying jizyah not only to the Christians and Jews, but to Zoroastrians and Sabæans, to worshippers of idols, of fire and of stone. [688] It was said that the Prophet himself had distinctly given directions that the Zoroastrians were to be treated exactly like “the people of the book,” i.e. the Jews and Christians, and that jizyah might also be taken from them in return for protection, [689]—a tradition that probably arose in the second century of the Hijrah, when apostolic sanction was sought for the toleration that had been extended to all the followers of the various faiths that Arabs had found in the countries they had conquered, whether such non-Muslims came under the category Ahl al-Kitāb or not. [690]