Valerian ( Publius Licinius Valerianus; c. 199 – 260 or 264) was Roman emperor from 253 to spring 260 AD. Valerian is known as the first Roman emperor to have been taken captive in battle, captured by the Persian emperor Shapur I after the Battle of Edessa, causing shock and instability throughout the Roman Empire. The unprecedented event and the unknown fate of the captured emperor generated a variety of different reactions and "new narratives about the Roman Empire in diverse contexts".

Unlike many of the would-be emperors and rebels who vied for imperial power during the Crisis of the Third Century, Valerian was of a noble and traditional senatorial family. Details of his early life are sparse, except for his marriage to Egnatia Mariniana, with whom he had two sons: Publius Licinius Egnatius Gallienus (his co-emperor and later successor) and Licinius Valerianus.

Valerian was consul for the first time either before AD 238 as a Suffectus or in 238 as an Ordinarius. In 238 he was princeps senatus, and Gordian I negotiated through him for senatorial acknowledgement for his claim as emperor. In 251 AD, when Decius revived the censorship with legislative and executive powers so extensive that it practically embraced the civil authority of the emperor, Valerian was chosen censor by the Senate, though he declined to accept the post. During the reign of Decius he was left in charge of affairs in Rome when that prince left for his ill-fated last campaign in Illyricum. Under Trebonianus Gallus Valerian was appointed dux of an army probably drawn from the garrisons of the German provinces which seems to have been ultimately intended for use in a war against the Persians.

However, when Trebonianus Gallus had to deal with the rebellion of Aemilianus in 253 AD, he turned to Valerian for assistance in crushing the attempted usurpation. Valerian headed south but was too late: Gallus was killed by his own troops, who joined Aemilianus before Valerian arrived. The Raetian soldiers then proclaimed Valerian emperor and continued their march towards Rome. Upon his arrival in September, Aemilianus's legions defected, killing Aemilianus and proclaiming Valerian emperor. In Rome, the Senate quickly acknowledged Valerian.

Valerian's first act as emperor was to appoint his son Gallienus augustus, thus making him co-emperor. Early in his reign, affairs in Europe went from bad to worse, and the whole West fell into disorder. In the East, Antioch had fallen into the hands of a Sassanid vassal and Armenia was occupied by Shapur I (Sapor). Valerian and Gallienus split the problems of the empire between them, with the son taking the West, and the father heading East to face the Persian threat.

In 254, 255, and 257, Valerian again became Consul Ordinarius. By 257, he had recovered Antioch and returned the province of Syria to Roman control. The following year, the Goths ravaged Asia Minor. In 259, Valerian moved on to Edessa, but an outbreak of plague killed a critical number of legionaries, weakening the Roman position, and the town was besieged by the Persians. In 260, probably in June, Valerian was decisively defeated in the Battle of Edessa and held prisoner for the remainder of his life. Valerian's capture was a tremendous defeat for the Romans.

Eutropius, writing between 364 and 378 AD, stated that Valerian "was overthrown by Shapur king of Persia, and being soon after made prisoner, grew old in ignominious slavery among the Parthians." An early Christian source, Lactantius (thought to be virulently anti-Persian, thanks to the occasional persecution of Christians by some Sasanian monarchs) maintained that, for some time prior to his death, Valerian was subjected to the greatest insults by his captors. For example, being used as a human footstool by Shapur when mounting his horse. According to this version of events, after a long period of such treatment, Valerian offered Shapur a huge ransom for his release.

In reply (according to one version), Shapur was said to have forced Valerian to swallow molten gold (the other version of his death is almost the same but it says that Valerian was killed by being flayed alive) and then had Valerian skinned and his skin stuffed with straw and preserved as a trophy in the main Persian temple.  It was further alleged that it was only after a later Persian defeat against Rome that his skin was given a cremation and burial.  The captivity and death of Valerian has been frequently debated by historians without any definitive conclusion.

The joint rule of Valerian and Gallienus was threatened several times by usurpers. Nevertheless, Gallienus held the throne until his own assassination in 268 AD.