Valerian (Publius Licinius Valerianus)vəlērˈēən, d. after 260, Roman emperor (253–60). He held important posts, both civil and military, under the emperors Decius and Gallus. After the short reign of the former general Aemilianus, Valerian was proclaimed emperor. In 257 he organized a general persecution of the Christians. Although not an incapable man, he was nevertheless unsuited to rule in such a critical time, for N Italy, Greece, and Asia Minor were falling to the barbarians and to the Persians. Appointing his son, Gallienus, as coregent, Valerian undertook a campaign in the East against Shapur I of Persia, who destroyed the Roman army and took (260) the emperor prisoner. Valerian died in captivity and was succeeded by Gallienus.