Dionysius Cassius, a celebrated Greek critic, was born about A.D. 213. His name, originally Dionysius, was changed for some unknown reason; and, besides the full title given above, he was also called Dionysius Longinus, or Cassius Longinus. According to some, he was born at Palmyra; others think that his intimate knowledge of Syriac, and the fact that his uncle was a native of Emesa, in Syria, indicate that he also was born in that city. From the circumstance, however, that Longinus, in his boyhood, seems to have been under the care and tuition of his uncle Fronto, the famous teacher of rhetoric at Athens, it is most probable that he was an Athenian by birth. On Fronto's death he became his heir; and, from one of his fragmentary works preserved by Porphyry, we learn that, in his earlier years, he travelled much, and thus formed an Longitude, intimacy with Ammonius Saccas, Origen, Plotinus, Ame- lius, and other philosophers. Under the instructions of the first two were imbued his admiration for Plato, which a subsequent familiarity with the works of that philosopher confirmed; and his sympathy with the spirit of the Pla- tonic philosophy, which he everywhere exhibits in the few of his comments on Plato's Dialogues that are extant. On completing his education, Longinus fixed his residence at Athens, and devoted the chief part of his time to the in- struction of young men in philosophy, criticism, rhetoric, and grammar. His most distinguished pupil was Malchus, whose Syriac name Longinus has changed into the Greek synonym, Porphyry. After sojourning for a considerable period at Athens, where he composed most of his works, Longinus travelled into the East; and on being invited by Queen Zenobia of Palmyra to become her instructor in Greek literature, settled in that city. On the demise of her husband soon afterwards, the queen, assuming the reins of government, appointed Longinus one of her counsellors. In this new capacity he persuaded her to shake off the Roman yoke, and dictated, it is said, a defiant letter to the Emperor Aurelian. This zeal was ungratefully employed by Zenobia as a shield to ward off the punishment of her revolt; for, when Palmyra was captured by the Romans, A.D. 273, Longinus was delivered up and condemned to death by order of the emperor. He met his doom with firmness.

So high did Longinus stand in the estimation of his con- temporaries, that Porphyry styled him "the critic;" and the phrase "κατά Λογγίνου σκοπεῖ" meant "to judge correctly." Not less noted was his erudition, so that Eunapius called him "a living library and walking museum." Of his numerous works, both philosophical and critical, the only one extant is his dissertation Ἐπική θέσις (On the Sublime), a treatise not more remarkable for the sagacity with which its canons of criticism are framed than for the judicious taste with which the passages adduced in support of these canons are selected from the best authors. The diction of the work, moreover, is a striking example of that forcible and elevated style which he endeavours to teach. Of the philosophical character of Longinus, almost the only note we have is that from Plotinus, who says, that "he was a philologer, but no philosopher." This taunt, however, loses the greater part of its value when we consider that its author probably set up, as his ideal of philosophy, the trifling and whimsical speculations of his own age. Though a pagan, Longinus was acquainted with the sacred Scriptures. In his famous treatise he quotes, as a specimen of the sublime, the passage from Genesis—"And God said, let there be light, and there was light." And in one of his extant fragments he ranks Paul of Tarsus, as he styles the apostle, with Demosthenes and the celebrated orators of Greece. Emanations, too, from the spirit of Christianity can be detected in his writings.

The best editions of the treatise On the Sublime are those of Pearce, London, 1724, 4to; 1773, 8vo; and of Morus, Leipzig, 1769-73, 8vo. The same work, together with all the surviving fragments of his other works, was published by Toepf, with notes by Ruhken, Oxford, 1778, 1789, and 1806, 8vo; by Weiske, Leipzig, 1809, 8vo; and by Egger, Paris, 1837, 16mo. Longinus has been translated into French by Boileau; into German by Schlosser, Leipzig, 1781; and into English by Smith, 1739, 1800.