The Ikhwān al-Ṣafā’ (Brethren of Purity), the anonymous adepts of a tenth-century esoteric fraternity based in Basra and Baghdad, hold an eminent position in the history of science and philosophy in Islam due to the wide reception and assimilation of their monumental encyclopaedia, the Rasāʾil Ikhwān al-Ṣafāʾ (Epistles of the Brethren of Purity). This compendium contains fifty-two epistles offering synoptic accounts of the classical sciences and philosophies of the age; divided into four classificatory parts, it treats with themes in mathematics, logic, natural philosophy, psychology, metaphysics, and theology, in addition to didactic fables.

The present volume, prepared by Ignacio Sánchez and James Montgomery, contains the first critical edition of the fourth epistle of this compendium and an annotated English translation.

Epistle 4: ‘On Geography’ contains a description of the Earth and its climes. It is of great significance for our understanding of both the Islamic geographical tradition and the world view of the Ikhwān al-Ṣafāʾ. It clearly shows that its authors were familiar with the Ptolemaic tradition, as the main sources used in its composition can be traced. But it is also a propaedeutic work which provides the intellectual tools needed to decipher the signs of God’s Creation, and to understand the phenomena of the sub-lunar world in terms of the cosmological order. This epistle epitomises many of the central themes in the conceptual universe of the Ikhwān al-Ṣafāʾ, such as the notion of science as a path to superior knowledge of God, and the relationship between microcosm and macrocosm as part of the divine design.