Plotinus (c. 204–270) was probably born in Roman Egypt, in the region of Lycopolis. He studied in Alexandria under the obscure Ammonius Saccas, joined the Emperor Gordian III's expedition against Persia 'to learn the wisdom of India and Persia', and after the campaign's collapse settled in Rome, where he taught for nearly thirty years. Thanks to his pupil and editor Porphyry's *Life of Plotinus*, his life is among the best-documented of antiquity.

Plotinus thought of himself as a commentator on Plato, but what he produced is more than commentary. He grounds all reality in three transcendent principles (*hypostases*). At the summit stands *the One* (*to Hen*) — beyond even being, of which no positive predicate can be uttered; we may only say what it is not. From the One, without any diminution of itself, *Nous* (*Intellect*) emanates — a pure mind that holds all the Forms in itself. From *Nous* in turn emanates *Soul* (*Psychê*), the principle that introduces time and motion and shapes the physical world. The material world is the faintest, most attenuated echo of this outflow.

The ethical counterpart of the cosmology is *return*. Because the human soul has come from *Nous* and ultimately from the One, it can — by a deep inward turning — flow back along the same path. Plotinus speaks of such a *henosis*, a union with the One, several times; Porphyry reports his master attained it four times in life. The mystical language is not a personal indulgence but the logical conclusion of the system.

The *Enneads* (*'Nines'*, because Porphyry arranged the fifty-four treatises into six groups of nine) appeared shortly after Plotinus's death. The system fed deeply into Christian theology — through Augustine and Pseudo-Dionysius into Eastern Christian mysticism — into Islamic philosophy through al-Farabi and Avicenna, into Jewish Kabbalah, into the Renaissance through Ficino, and from there into modern idealism. When the Emperor Justinian closed the Academy of Athens in 529 CE and ancient philosophy formally ended, the world that was being shut down was, more than anyone's, Plotinus's.