|266 by topic|
|Ab urbe condita||1019|
|Balinese saka calendar||187–188|
|Chinese calendar||乙酉年 (Wood Rooster)|
2962 or 2902
— to —
丙戌年 (Fire Dog)
2963 or 2903
|Coptic calendar||−18 – −17|
|- Vikram Samvat||322–323|
|- Shaka Samvat||187–188|
|- Kali Yuga||3366–3367|
|Iranian calendar||356 BP – 355 BP|
|Islamic calendar||367 BH – 366 BH|
|Minguo calendar||1646 before ROC|
|Seleucid era||577/578 AG|
|Thai solar calendar||808–809|
392 or 11 or −761
— to —
393 or 12 or −760
Year 266 (CCLXVI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Gallienus and Sabinillus (or, less frequently, year 1019 Ab urbe condita). The denomination 266 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- 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".
- The rule of High King Cormac mac Airt ends (approximate date).
- 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 "Emperor Wu of Jin". He establishes his capital at Luoyang and gives his male relatives independent military commands throughout his empire.
- Wang Chen, Chinese official and historian
- Wang Fan, Chinese official, mathematician and astronomer (b. 228)