At the core of that vast civilization was a common commitment to Islam. No group was more important in the transmission of those beliefs and practices than the ulama. These learned scholars were not “priests” in the Christian sense, for in Islam, at least theoretically, no person could stand between the believer and Allah. Rather, they served as judges, interpreters, administrators, prayer leaders, and reciters of the Quran, but especially as preservers and teachers of the sharia. Supported mostly by their local communities, some also received the patronage of sultans, or rulers, and were therefore subject to criticism for corruption and undue submission to state authority. In their homes, mosques, shrines, and Quranic schools, the ulama passed on the core teachings of the faith. Beginning in the eleventh century, formal colleges called madrassas offered more advanced instruction in the Quran and the sayings of Muhammad; grammar and rhetoric; sometimes philosophy, theology, mathematics, and medicine; and, above all else, law. Teaching was informal, mostly oral, and involved much memorization of texts. It was also largely conservative, seeking to preserve an established body of Islamic learning.

The ulama were an “international elite,” and the system of education they created served to bind together an immense and diverse civilization. Common texts were shared widely across the world of Islam. Students and teachers alike traveled great distances in search of the most learned scholars. From Indonesia to West Africa, educated Muslims inhabited a “shared world of debate and reference.”29

Paralleling the educational network of the ulama were the emerging religious orders of the Sufis. By the tenth century, particular Sufi shaykhs (shakes), or teachers, began to attract groups of disciples who were eager to learn their unique devotional practices and techniques of personal transformation. The disciples usually swore allegiance to their teacher and valued highly the chain of transmission by which those teachings and practices had come down from earlier masters. In the twelfth and thirteenth centuries, Sufis began to organize in a variety of larger associations, some limited to particular regions and others with chapters throughout the Islamic world. The Qadiriya order, for example, began in Baghdad but spread widely throughout the Arab world and into sub-Saharan Africa.

Sufi orders were especially significant in the frontier regions of Islam because they followed conquering armies or traders into Central and Southeast Asia, India, Anatolia, parts of Africa, and elsewhere. Their devotional teachings, modest ways of living, and reputation for supernatural powers gained a hearing for the new faith. Their emphasis on personal experience of the Divine, rather than on the law, allowed the Sufis to accommodate elements of local belief and practice and encouraged the growth of a popular or blended Islam. The veneration of deceased Sufi “saints,” or “friends of God,” particularly at their tombs, created sacred spaces that enabled Islam to take root in many places despite its foreign origins. But that flexibility also often earned Sufi practitioners the enmity of the ulama, who were sharply critical of any deviations from the sharia.

Like the madrassas and the sharia, Sufi religious ideas and institutions spanned the Islamic world and were yet another thread in the cosmopolitan web of Islamic civilization. Particular devotional teachings and practices spread widely, as did the writings of such famous Sufi poets as Hafiz and Rumi. Devotees made pilgrimages to the distant tombs of famous teachers, who, they often believed, might intercede with God on their behalf. Wandering Sufis, in search of the wisdom of renowned shaykhs, found fellow seekers and welcome shelter in the compounds of these religious orders.

In addition to the networks of the Sufis and the ulama, many thousands of people, from kings to peasants, made the grand pilgrimage to Mecca—the hajj—no doubt gaining some sense of the umma. There men and women together, hailing from all over the Islamic world, joined as one people to rehearse the central elements of their faith. The claims of local identities based on family, clan, tribe, ethnicity, or state never disappeared, but now overarching them all was the inclusive unity of the Muslim community.