GALLIENUS, P. Licinius (218-268), Roman emperor, son of the emperor Valerian, was born about 218. From 253 to 260 he reigned conjointly with his father, and gave proof of both bravery and ability, especially in the defeat near Milan of 300,000 Alemanni, with a force of only 10,000 Romans. When, however, his father was defeated and taken prisoner by Sapor, king of Persia, in 260, Gallienus made no effort to obtain his release, or to withstand the incursions of the invaders who threatened the empire from all sides. He occupied part of his time in dabbling in literature, science, and various trifling arts, but gave himself up chiefly to excess and debauchery. His generals rebelled against him in almost every province of the empire, and this period of Roman history came to be called the reign of the thirty tyrants, although in reality the usurpers numbered only nineteen. Gallienus was killed at Milan in 268 while besieging Aureolus, who had been proclaimed emperor by the Illyrian legions.