Longinus, DIONYSIUS CASSIUS, a famous Platonic philosopher and rhetorician of the 3d century, born at Enesa or at Athens, about 213 A.D. He studied at Alexandria, under Ammonius, and he himself taught rhetoric in Athens, where the famous Porphyry was a pupil. Later he settled at Palmyra, and became chief counsellor to the celebrated Queen Zenobia, whom he abetted in her determination to shake off the Roman yoke. For this he was beheaded as a traitor, by command of the Emperor Aurelian, 273 A.D. The only work of his that remains is the famous treatise Peri Hypousos
('On the Sublime'), the authenticity of which has been impugned. There are editions by Egger (1837) and Otto Jalm (1867). See Vaucher's Études critiques sur le Traité du Sublime (Geneva, 1854).