The Brethren of Purity (Arabic: ????? ?????; transliteration: Ikhwan al-Safa; also in English: The Brethren of Sincerity) were a secret society of Muslim philosophers in Basra, Iraq, in the 10th century CE. The structure of this mysterious organization and the identities of its members have never been clear. Their esoteric teachings and philosophy are expounded in an epistolary style in the Encyclopedia of the Brethren of Purity (Arabic: Rasa'il Ikhwan al-safa'), a giant compendium of 52 epistles that would greatly influence later encyclopedias. A good deal of Muslim and Western scholarship has been spent on just pinning down the identities of the Brethren and the century in which they were active.