  Our brief survey of the philosophical production in Byzantium starts in the 9th century with the work of the patriarch of Constantinople, Photios (c. 810–after 893), though there is evidence of elementary teaching of logic and ethics in the 7th and 8th centuries, during the period of Iconoclasm. The most important philosophical work from this period is the Dialectica, the first part of John of Damascus’ (c. 675–749) widely influential Source of Knowledge, which draws mainly on the late antique commentators on Porphyry’s Isagoge and Aristotle’s logical works. Unfortunately, the only surviving works by Leo the Mathematician (c. 790–after 869), who taught Aristotelian logic at the Magnaura School in Constantinople, established soon after the end of Iconoclasm, are some notes in manuscripts containing Platonic dialogues.