At the intersection of continents, between Asia and the Middle East, in southern Iraq, Basra, an anonymous group of scholars gathered to record the sciences of their day. This was shortly before the end of the tenth century, when Islamic theology and law had yet to crystallise, and philosophy was as strong as it would ever be. The authors, collectively known as the Brethren of Purity (al-Ikhwan al-Safa), produced a fifty-two-volume encyclopedia, which became known simply as their Epistles (Rasa’il). The range of the work was truly comprehensive. It was divided into four parts:

• 1. The mathematical sciences (with volumes on logic, geometry, astronomy, geography and music).

• 2. The sciences of natural bodies (with volumes on meteorology, minerals, plants and embryology).

• 3. The psychological and rational sciences (with volumes on movement, epochs and eras, and cause and effect).

• 4. Theology (with volumes on magic, talismans, prayer and beliefs).

Historians have recognised the wide-ranging sweep of this encyclopedia, which draws upon ‘Pythagorean and Nichomachian arithmetic, numerology and music, Hermetic and Indo-Persian magic and astrology, Aristotelian logic and physics, Gnostic esotericism, neo-Platonic cosmology, theory of emanations and metaphysics, Biblical and Qur’anic prophetology, Platonic concepts of law and leadership, and Buddhist, Zoroastrian and Manichean wisdom and allegory’. It also draws upon the beliefs of the Mandaans, a minority religious group discussed by Professor Charles Häberl in this volume. As a collection, the Rasa’il provide a unique window onto the formative period of medieval thought, when various pre-Islamic sciences were still contested. The authors aim not only to be exhaustive, but also to present their material in an accessible form, with the intention of facilitating the widest possible reception. By any measure, the tone of the work is strikingly cosmopolitan. While scholarship has established that the authors were likely Isma‘ili Shia in their personal commitments, this Epistle is neither dogmatic nor exclusivist when treating matters of culture or religion. Shi’a perspectives are represented, but thanks to the work's breadth and openness, its subsequent life in Islamic intellectual history has transcended communal divisions, allowing the encyclopedia an unparalleled role in the transmission of philosophical and scientific ideas. In this spirit the Brethren repeatedly enjoin us to follow their lead, and to draw knowledge from all sources, regardless of origin.