Gallienus (Publius Licinius Valerianus Egnatius) (găl´īē´nəs), d. 268, Roman emperor. He ruled as the colleague (253–60) of his father, Valerian, and alone (260–68). When his father was in the East, Gallienus checked the Alemanni near Milan, and even after the capture of Valerian he was successful. Later, however, the provinces began to be too rebellious for his control. Postumus had established his independence in Gaul, and in the East Odenathus, spreading the conquests of Palmyra, was being recognized. A force sent by Gallienus against Zenobia was defeated. Gallienus himself was murdered by his men at Milan, where he was resisting a revolt, which was eventually suppressed by his successor Claudius II. During his reign Gallienus had reversed his father's program of persecuting the Christians and had managed to bring the empire through a crucial period of history without complete disaster.