one of the most able and successful among the generals of M. Aurelius, was a native of Cyrrhus in Syria, son of a certain Heliodorus, who in consequence of his eminence as a rhetorician had risen to be praefect of Egypt. While Verus was abandoning himself to all manner of profligacy at Antioch, the war against the Parthians was vigorously prosecuted by Cassius, who closed a most glorious campaign by the capture of Seleuceia and Ctesiphon. He subsequently quelled a formidable insurrection in Egypt, organized by a tribe of marauders who dwelt among the fens; and having been appointed governor of all the Eastern provinces, discharged his trust for several years with fidelity and firmness. The history of his rebellion and his miserable death are narrated under M. AURELIUS. If we can believe in the authenticity of the documents produced by Gallicanus, the conduct of Cassius excited the suspicion of Verus at a very early period, but Antoninus refused to listen to the representations of his colleague, ascribing them doubtless, and with good cause, to jealousy. (In addition to the notices contained in Dio Cassius 71.2, 21, &c., we have a formal biography from the pen of one of the Augustan historians, named Vulcatius Gallicanus, but the style of this production is not such as to inspire much confidence in its author.)
[W.R]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890