men seek an alternative. The great social and economic changes of the eighth and ninth centuries had brought wealth and power to some, hardship and frustration to others. In the countryside, the growth of large and, often, fiscally privileged estates was accompanied by the impoverishment and subjection of tenants and smallholders; in the towns, the development of commerce and industry created a class of journeyman labourers, and attracted an unstable and floating population of rootless and needy migrants. Amid great prosperity, there was also great distress. The dry legalism and remote transcendentalism of the orthodox faith, the cautious conformism of its accredited exponents, offered little comfort to the dispossessed, little scope for the spiritual yearnings of the uprooted and unhappy. There was an intellectual malaise, too. Muslim thought and learning, enriched from many sources, were becoming more subtle, more sophisticated, more diverse. There were great and agonizing problems to be considered, arising from the confrontation of Islamic revelation, Greek science and philosophy, Persian wisdom, and the hard facts of history. Among many, there was a loss of confidence in traditional Islamic answers, and a desire, of growing urgency, for new ones. The great Islamic consensus - religious, philosophical, political, social - seemed to be breaking up; a new principle of unity and authority, just and effective, was needed to save Islam from destruction.
It was the great strength of the Ismailis that they could offer such a principle - a design for a new world order under the Imam. To both the devout and the discontented, the message and ministrations of the dais brought comfort and promise. To philosophers and theologians, poets and scholars, the Ismaili synthesis offered a seductive appeal. Because of the strong reactions against the Ismailis in later times, most of their literature disappeared from the central lands of Islam, and was preserved only among the sectaries themselves. But a few works of Ismaili inspiration have for long been widely known, and many of the great classical authors in Arabic and Persian show at least traces of Ismaili influence. The `Epistles of the Sincere Brethren', a famous encyclopaedia of religious and worldly knowledge compiled in the tenth century, is saturated with Ismaili thought, and exercised a profound influence on Muslim intellectual life from Persia to Spain.
Not surprisingly, the dais achieved special success in those places, like Southern Iraq, the shores of the Persian Gulf, and parts of Persia, where earlier forms of militant and extremist Shi'ism had already won a following, or where local cults offered favourable ground. At the end of the ninth century a branch of the sect known as the Carmathians - their precise relationship with the main Ismaili body is uncertain - was able to win control and establish a form of republic in Eastern Arabia, which served them for more than a century as a base for military and propagandist operations against the Caliphate. A Carmathian attempt to seize power in Syria at the beginning of the tenth century failed, but the episode is significant and reveals some local support for Ismailism even at that early date.
The greatest triumph of the Ismaili cause came in another quarter. A mission to the Yemen had, by the end of the ninth century, won many converts and a base of political power; from there further missions were despatched to other countries, including India and North Africa, where they achieved their most spectacular success. By 9o9 they were strong enough for the hidden Imam to emerge from hiding and proclaim himself Caliph in North Africa, with the title al-Mahdi, thus founding a new state and dynasty. They were known as the Fatimids, in token of their descent from Fatima, the daughter of the Prophet.
In the first half-century, the Fatimid Caliphs ruled in the west only, in North Africa and Sicily. Their eyes, however, were on the East, the