Publins Licnius Egnatins Gallienus, a Roman emperor, son of the emperor Valerian, born about A. D. 235, died in 268. On Valerian's accession to the throne in 253 he immediately associated his son with himself in the government with the title of Caesar. The old emperor sent him, under the care of Postumus, governor of Gaul, to repel the incursions of the Franks and Alemanni on the upper Danube and the Rhine, where Gallienus displayed considerable ability and bravery. On hearing of his father's defeat and capture by Sapor, king of Persia (2G0), he made no effort to obtain his release, but succeeded with evident pleasure to his throne and title, and gave himself up to debauchery, viewing with like indifference the invasions of the empire by the barbarians and its dismemberment by usurpers. The Franks overran Gaul and Spain, and even crossed over to Africa; the Alemanni ravaged the provinces of the upper Danube; the Goths pillaged the cities of Asia on the southern shore of the Euxine; and the Persians, after taking possession of Mesopotamia, passed over to Syria and captured Antioch. This was followed by the plague. Nearly 30 of his armies in different parts of the empire each elected their general to be emperor, and the military anarchy which succeeded has been called the age of the 30 tyrants.

When the legions of lllyria in 268 proclaimed Aureolus emperor, he immediately marched on Rome. Gallienus, awakening from his apathy, marched against the usurper, defeated him in a battle near the Adda, and then besieged him in Milan, but was murdered by conspirators. Gallienus was a poet and rhetorician.