Publius Licinius Egnatius Gallienus, (died AD 268), Roman Emperor, 260-68, and co-regent with Valerian, his father, from 253 until the latter’s capture by the Persians in 260. Gallienus’s reign is known as ‘the period of the thirty tyrants’, for usurpers arose throughout the provinces. The most prominent, Aureolus, was proclaimed emperor in Illyricum, invaded Italy, and captured Milan. While besieging him in that city, Gallienus was murdered by his own troops. He was succeeded by Claudius II.