Battle of Edessa: With a large army, said to number 70,000 men, Valerianus attempts to drive the Persians back from Edessa. The Roman army is surrounded and most of its troops are killed or captured. Valerianus is taken prisoner for the remainder of his life.
Emperor Gallienus tries twice to crush the usurper Postumus, but on the first occasion Aureolus, commander of the elite cavalry, carelessly lets him escape. The second time, Gallienus sustains an arrow wound and has to break off his siege of a Gallic town where Postumus has holed up. He makes no other serious attempt to overcome his rival, instead devoting his attention to the political and military problems in the Danube and eastern parts of the Roman Empire.
Postumus makes no move to march on Rome and claim his territory south of Gaul.
A general of Gallienus' army, Victorinus, defects to Postumus.
Sima Zhao, who had been the regent and de facto primary authority of the state of Cao Wei for little over 10 years by this point, passes away, leaving his authority to his eldest son, Sima Yan, who will go on to disestablish the state of Cao Wei in 266, founding the Jin dynasty.
King Odaenathus of Palmyra invades Persia to conquer the capital, Ctesiphon, and twice comes as far as the walls of the Persian capital, but fails to take it. After his victories in the East, he pronounces himself with the title "king of kings".
A powerful tropical volcanic eruption around this year brings a below-average flood of the Nile next year.
February 4 – Sima Yan, regent of the Chinese state of Cao Wei, forces the last Cao Wei emperor Cao Huan to abdicate in his favour. The Cao Wei state's existence comes to an end. Sima Yan establishes the Jin Dynasty, and becomes its first emperor on 8 February, and is historically known as "Wu of Jin". He establishes his capital at Luoyang, and gives his male relatives independent military commands throughout his empire.