3rd-century philosophers

Plotinus (Greek: Πλωτῖνος, Plōtinos; c. – 270) was a major Hellenistic philosopher who lived in Roman Egypt. In his philosophy, described in the Enneads, there are three principles: the One, the Intellect, and the Soul. His teacher was Ammonius Saccas, who was of the Platonic tradition. Historians of the 19th century invented the term Neoplatonism and applied it to Plotinus and his philosophy, which was influential during Late Antiquity and the Middle Ages. Much of the biographical information about Plotinus comes from Porphyry's preface to his edition of Plotinus' Enneads. His metaphysical writings have inspired centuries of Pagan, Jewish, Christian, Gnostic, and Islamic metaphysicians and mystics, including developing precepts that influence mainstream theological concepts within religions, such as his work on duality of the One in two metaphysical states. This concept is similar to the Christian notion of Jesus being both god and man, a foundational idea in Christian theology.

Amelius (Greek: Ἀμέλιος), whose family name was Gentilianus, was a Neoplatonist philosopher and writer of the second half of the 3rd century.

Porphyry of Tyre (Greek: Πορφύριος, Porphýrios; Arabic: فرفوريوس‎, Furfūriyūs; c.– c.) was a Phoenician Neoplatonic philosopher born in Tyre, Roman Syria during Roman rule. He edited and published The Enneads, the only collection of the work of Plotinus, his teacher. His commentary on Euclid's Elements was used as a source by Pappus of Alexandria.

Arius (Koinē Greek: Ἄρειος, Áreios; 250 or 256–336) was a Cyrenaic presbyter, ascetic, and priest best known for the heretical doctrine of Arianism. His teachings about the nature of the Godhead in Christianity, which emphasized God the Father's uniqueness and Christ's subordination under the Father, and his opposition to what would become the dominant Christology, Homoousian Christology, made him a primary topic of the First Council of Nicaea convened by Emperor Constantine the Great in 325.

Aelius Galenus or Claudius Galenus (Greek: Κλαύδιος Γαληνός; September 129 – c./c.), often Anglicized as Galen and sometimes known as Galen of Pergamon (), was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of the most accomplished of all medical researchers of antiquity, Galen influenced the development of various scientific disciplines, including anatomy, physiology, pathology, pharmacology, and neurology, as well as philosophy and logic.

Origen of Alexandria (c. 184 – c. 253), also known as Origen Adamantius, was an early Christian scholar, ascetic, and theologian who was born and spent the first half of his career in Alexandria. He was a prolific writer who wrote roughly 2,000 treatises in multiple branches of theology, including textual criticism, biblical exegesis and hermeneutics, homiletics, and spirituality. He was one of the most influential figures in early Christian theology, apologetics, and asceticism. He has been described as "the greatest genius the early church ever produced".

Fronto of Emesa is a famous rhetorician and uncle of Cassius Longinus. Fronto taught rhetoric in Athens. He died in Athens, aged about 60.

Origen the Pagan (Greek: Ὠριγένης; fl. early 3rd century) was a Platonist philosopher who lived in Alexandria. He was a student of Ammonius Saccas and a contemporary of Plotinus in Ammonius's philosophy school in Alexandria. It is possible that he was the famous Christian philosopher and theologian Origen of Alexandria, who was educated by Ammonius Saccas.

Cassius Longinus (Greek: Κάσσιος Λογγῖνος; c. 213 – 273 AD) was a rhetorician and philosophical critic. He was perhaps a native of Emesa in Syria. He studied at Alexandria under Ammonius Saccas and Origen the Pagan, and taught for thirty years in Athens, one of his pupils being Porphyry. Longinus did not embrace the Neoplatonism then being developed by Plotinus, but continued as a Platonist of the old type and his reputation as a literary critic was immense. During a visit to the east, he became a teacher, and subsequently chief counsellor to Zenobia, queen of Palmyra. It was by his advice that she endeavoured to regain her independence from Rome. Emperor Aurelian, however, crushed the revolt, and Longinus was executed.

Proclus (or Proklos) Mallotes (Greek: Πρόκλος Μαλλώτης) was a Stoic philosopher and a native of Mallus in Cilicia. According to the Suda he was the author of the following books: