This book presents an English-language translation of Risālā-yi Muʿīnīya, or the Muʿīnīya Epistle. Risālā-yi Muʿīnīya is one of the earliest known works of Naṣīr al-Dīn Ṭūsī (1201–1274), an intellectual luminary of the 13th century CE. The work is notable for the choice of Ṭūsī’s native Persian as the language of the text. In addition, Ṭūsī organized his volume into a four-part structure, which went on to become a popular template for the Islamic astronomers who succeeded him.  

This book helped ensure the patronage of...