Dionysius Cassias Longinus, a Greek critic, born in Athens, or at Emesa in Syria, about A. D. 213, executed at Palmyra in 273. He studied under his uncle Phronto of Emesa, a teacher of rhetoric at Athens, visited many countries, heard the lectures of the philosophers Ammonius Saccas and Origen, made himself familiar with the works of Plato, and opened a school of philosophy, criticism, and rhetoric at Athens. He subsequently removed to the East, and having been invited to the court of Zenobia, queen of Palmyra, he became not only her literary instructor, but also her principal political counsellor. Zenobia was desirous of throwing off the Roman yoke, and making good her right to supreme sovereignty by force of arms. Longinus encouraged and advised her, and on the capture of Palmyra was put to death by order of the emperor Aurelian. He was the ablest philosophical writer of his age. The doctrine of the universal influence of soil and climate on the intellectual capacities and on the civilization of mankind is especially due to him.

The only important fragment of his voluminous works now extant is a portion of his celebrated treatise "On the Sublime." The first edition of this fragment is that of Robortello (Basel, 1554), the best that of Moras (Leipsic, 1769-'73). It has been translated into English by William Smith (London, 1739). Complete editions of all his extant writings were published at Leipsic in 1809, at Oxford in 1820, and at Paris in 1837.