 The Ikhwân al-Safâ’ or “Brethren of Purity”, as their name is commonly translated, are the authors of one of the most complete Medieval encyclopedias of sciences, antecedent at least two centuries to the best known in the Latin world (by Alexander Neckham, Thomas de Cantimpré, Vincent de Beauvais, Bartholomaeus Anglicus, all dating back to the 13th century). The “encyclopedia” is a collection of Epistles, the Arabic title of which is Rasâ’il Ikhwân al-Safâ’ wa Khullân al-Wafâ’ (Epistles of the Pure Brethren and the Sincere Friends). It consists of extremely heterogeneous materials, reworked to represent the whole educational training intended for an élite (see later). It is very well known, and a great deal of research into it has been done by Eastern and Western scholars, but the variety of topics addressed and the questions raised as to the identity and ideology of its authors remain unsolved. In an isolated form, and under a false attribution, some of these treatises came to the Latin Middle Ages through the Spanish version by Maslama al-Majrîtî, which is traditionally placed at the beginnings of the 11th century. This already discussed chronology (Carusi 2000, 494–500) is recently questioned by several scholars. The development of research in this direction was encouraged by the pioneer study, Fierro 1996, part. 94 and 106–108; cf. also Hamdani 1978, 350; Hamdani, Soufan 2019, 11-12 (see infra).