stands second on the list of the thirty tyrants enumerated by Trebellius Pollio [see AUREOLUS]. His full name was M. Cassianus Latinius Postumus. Of humble origin, he owed his advancement to merit, was nominated by Valerian, who entertained the strongest conviction of his worth, governor of Gaul, and was entrusted specially with the defence of the Rhenish frontier. By his aid Gallienus was enabled to repulse for some years the attacks of the barbarians; but on setting out for Illyria (A. D. 257), in order to quell the insurrection of Ingenuus [INGENUUS], he committed his son Saloninus to the guardianship of Silvanus. Postumus, feeling slighted by this arrangement, took advantage of the disaffection of the troops towards the royal family, raised the standard of rebellion, assumed the style and title of emperor, and drove Saloninus to take refuge in Colonia Agrippina, where he was besieged, and eventually put to death upon the capture of the city. These events took place in A. D. 258 and 259, while Valerian was prosecuting his unfortunate campaign against the Persians. Whatever guilt may attach to the circumstances under which Postumus established his sway--and these are differently represented by different authorities, since Pollio declares that he was urged on by the discontent of the army and the provincials rather than by any ambition of his own, denying, at the same time, that he had any hand in the death of the youth whom he represents as having been actually consigned to his protection--it seems certain that he exercised his power with firmness, moderation, and skill. Not only were the efforts of Gallienus to take vengeance for his son signally frustrated; but while the nominal sovereign was indulging in slothful pleasures, the pretender, beloved by all to whom his influence extended, maintained a strong and just government, and preserved Gaul from the devastation of the warlike tribes upon the eastern border. Hence the titles of Imperator and Germanicus Maximus, which recur upon the medals of several successive years, are in this case something better than a mere empty boast. At length, however, his fickle subjects became weary of submitting to the strict and well-regulated discipline enforced in all departments of the state, rallied round a new adventurer named Laelianus [LAELIANUS; LOLLIANUS], and Postumus, who assuredly may claim the highest place among the numerous pageants of royalty that sprung up and disappeared with such rapidity during this disturbed epoch, was slain A. D. 267, in the tenth year of his reign. The number of coins still extant bearing the effigy of this prince, and the skilful workmanship displayed in the gold pieces especially, prove that the arts of peace were not despised in his court, while the letters S. C. stamped after the usual fashion upon the brass money, seem to indicate that he had surrounded himself with a body of counsellors, whom he chose to consider the true Roman senate.

All questions connected with this reign have been investigated, with much diligence, accuracy, and learning, by Brequigny in the vol. xxx. p. 338, &c. There is also a dissertation on the Life of Postumus by Ioach. Meierus, preserved in Walterek Elect. p. 203. The chief ancient authorities are, Trebell. Poll. Trig. Tyrann. ii.; Aurel.