The Encyclopedia of the Brethren of Purity (Arabic: رسائل أخوان الصفا و خلان الوفا‎ Rasa'il ikhwan as-safa' wa khillan al-wafa; 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 in 52 treatises (or "rasa'il") written by the mysterious Brethren of Purity of Basra, Iraq sometime in the second half of the 900s CE (or possibly later, in the 1000s). It had a great influence on later intellectual leading lights of the Muslim world, such as Ibn Arabi and was transmitted as far abroad within the Muslim world as Al-Andalus (Spain). The Encyclopedia contributed to the popularization and legitimization of Platonism in the Arabic world.