Plotinus, usually considered the founder of Neoplatonism, was probably born in Lykopolis, Upper Egypt, and he may have been a Hellenized Egyptian rather than a Greek. He turned to the study of philosophy when he was twenty-eight. Disappointed by several teachers in Alexandria, he was directed by a friend to Ammonius Saccas, who made a profound impression on him. Of Ammonius's teachings we know extremely little, but a promising line of investigation has been opened up in a comparison of Plotinus's doctrines with those of Origen the Christian, also a student of Ammonius. Of other students of Ammonius, Origen the Pagan and Longinus deserve special mention.

Plotinus was Ammonius's pupil for eleven years. He left Ammonius to join the expeditionary army of Emperor Gordianus III that was to march against Persia, hoping to acquire firsthand knowledge of Persian and Indian wisdom, in which he...