Neoplatonism is a modern term used to designate the period of Platonic philosophy beginning with the work of Plotinus and ending with the closing of the Platonic Academy by the Emperor Justinian in 529 CE. This brand of Platonism, which is often described as ‘mystical’ or religious in nature, developed outside the mainstream of Academic Platonism.
The origins of Neoplatonism can be traced back to the era of Hellenistic syncretism which spawned such movements and schools of thought as Gnosticism and the Hermetic tradition. A major factor in this syncretism, and one which had an immense influence on the development of Platonic thought, was the introduction of the Jewish Scriptures into Greek intellectual circles via the translation known as the Septuagint.
The encounter between the creation narrative of Genesis and the cosmology of Plato’s Timaeus set in motion a long tradition of cosmological theorizing that finally culminated in the grand schema of Plotinus’ Enneads. Plotinus’ two major successors, Porphyry and Iamblichus, each developed, in their own way, certain isolated aspects of Plotinus’ thought, but neither of them developed a rigorous philosophy to match that of their master.
It was Proclus who, shortly before the closing of the Academy, bequeathed a systematic Platonic philosophy upon the world that in certain ways approached the sophistication of Plotinus. Finally, in the work of the so-called Pseudo-Dionysius, we find a grand synthesis of Platonic philosophy and Christian theology that was to exercise an immense influence on mediaeval mysticism and Renaissance Humanism.