Plotinus, a Neo-Platonic philosopher, born in Lycopolis, Egypt, about A. D. 204, died at Puteoli about 270. At the age of 28 he went to Alexandria, and attended the lectures of Ammonius Saccas, the founder of the eclectic school, with whom he remained 11 years. In 242 he accompanied the emperor Gordian's expedition against the Persians, in order to study the philosophy of the East; and on the death of the monarch (244) he barely escaped with his life to Antioch. He then went to Rome, and taught the doctrines of Ammonius, but only orally, as he had agreed to keep them secret; and although his fellow pupils, Herennius and Origen, began to publish them, he did not follow their example until the first year of the reign of Gallienus (254). Ten years later, when Porphyry became his pupil, he had written 21 books, and subsequently composed 33 more. In Rome, where he remained until his death, he was a great favorite not only with men of science, but with senators and statesmen; and so great was the confidence reposed in him, that many Romans on their deathbeds made him the guardian of their children and estates.

Gallienus was so much attached to him, that had it not been for the efforts of some of the courtiers he would have rebuilt two cities in Campania to afford Plotinus an opportunity of founding a commonwealth modelled after the ideal republic of Plato. Plotinus never corrected nor read through a second time his manuscript, and paid no attention to spelling or the division of syllables. His handwriting was execrable, and as his thoughts were put down without any systematic connection, he is one of the most obscure writers to be found in any language. His productions, revised by his pupil Porphyry, are in 54 books, called the Enneads, and treat of the most abstract subjects of thought, such as " Entity and Unity," "The Essence of the Soul," and " The Unity of the Good." According to his biographer, Porphyry, so ashamed was he that he existed in the body, that he would neither reveal his parentage, his ancestry, his native country, nor the day of his birth. So great was his contempt for the body, that he had no concern for his health, and was very scanty in the use of food, generally refraining from meat altogether. In spite of their obscurity, his writings have exercised some influence upon modern philosophy, having been diligently studied by Cudworth, Henry More, Norris, Gale, and others.

There is a striking resemblance between the doctrines of Plotinus and the pantheistic ideas of Spinoza, evinced in the treatise of the former written to show that all being is one and the same. His life by Porphyry is the only authority upon his history. The Enneads were first translated into Latin by Marsilius Ficinus (Florence, 1492). In 1835 the entire Greek text was first published by Oreuzer (3 vols. 4to, Oxford). The "Select Works of Plotinus " have been translated into English by Thomas Taylor (London, 1834); and a French version of the Enneads by M. Bouillet was completed in 1861 (3 vols. 8vo, Paris).