in the course of their incursion, they received a new coherence by the rise of the religion of Islam and, by the racial unity thus artificially produced, became more formidable. In their outspread over Egypt and Western Asia the Arabs adopted the policy, partly deduced from the Qurʾan and partly based on the tradition of the first Khalif’s conduct in Arabia, of uncompromising warfare against all “polytheists,”—the creed of Islam was a pure unitarianism, and could contemplate no toleration of polytheism,—but of accommodation with those possessed of the divine revelation, even in the imperfect and corrupt form known to Christians and Jews. These “People of the Book” were not pressed to embrace Islam, but might remain as tribute-paying subjects of the Muslim rulers, with their own rights very fully secured. In all the conquered lands the progress of the Muslim religion was very gradual, and in all of them Christian and Jewish communities have maintained an independent continuous existence to the present day. Yet for all this there were very many conversions to the religion of the ruling race, and these were so numerous that within the first century of the Hijra the Arabs themselves were in a numerical minority in the Church of Islam. The alien converts, socially and intellectually developed in the culture of the Hellenistic world or of semi-Hellenistic Persia, were very far in advance of the ruling Arabs who were little better than half savages at the commencement of their career of conquest: and the unexpected inclusion of this more cultured element acted as a leaven in the Islamic community, and forced it to a rapid and somewhat violent evolution. It is wonderful that Islam had sufficient vigour and elasticity to be able to absorb such fresh elements and phases of thought, but that elasticity had its limits, and at a very early date sects began to form whose members the orthodox felt themselves unable to recognise as fellow Muslims.