Plotinus (204-270 CE) taught in Rome; his student Porphyry edited the Enneads. The system: the One beyond being, from which emanates Nous (Mind), then Soul, then the sensible world; evil is not a substance but distance from source. Porphyry, Iamblichus, and Proclus extended it; Augustine and Pseudo-Dionysius rerouted it into Christianity.
The undergraduate summary: Neoplatonism as Plato plus incense, dismissed as the twilight of Greek rationalism. The Enneads repay actual reading with some of antiquity's tightest arguments, which the twilight framing skips.
The influence map: emanation, levels, return, is the schematic under Kabbalah's Tree, Sufi ascent, Christian mysticism, and half the iceberg on the poster. Plotinus may be the most quoted-unread author in the Western esoteric tradition.
If everything flows from the One, why does anything here feel like a departure?