The Encyclopedia of the Brethren of Purity (Arabic: رسائل إخوان الصفا‎‎) also variously known as the Epistles of the Brethren of Sincerity, Epistles of the Brethren of Purity and Epistles of the Brethren of Purity and Loyal Friends was a large encyclopedia[1] in 52 treatises (rasā'il) written by the mysterious[2] Brethren of Purity of Basra, Iraq sometime in the second half of the 10th century CE (or possibly later, in the 11th century). It had a great influence on later intellectual leading lights of the Muslim world, such as Ibn Arabi,[3][4] and was transmitted as far abroad within the Muslim world as Al-Andalus.[5][6] The Encyclopedia contributed to the popularization and legitimization of Platonism in the Islamic world.[7]