Year 311 (CCCXI) 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 Valerius and Maximinus (or, less frequently, year 1064 Ab urbe condita). The denomination 311 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.
|Ab urbe condita||1064|
|Balinese saka calendar||232–233|
|Chinese calendar||庚午年 (Metal Horse)|
3007 or 2947
— to —
辛未年 (Metal Goat)
3008 or 2948
|- Vikram Samvat||367–368|
|- Shaka Samvat||232–233|
|- Kali Yuga||3411–3412|
|Iranian calendar||311 BP – 310 BP|
|Islamic calendar||321 BH – 320 BH|
|Minguo calendar||1601 before ROC|
|Seleucid era||622/623 AG|
|Thai solar calendar||853–854|
437 or 56 or −716
— to —
438 or 57 or −715
- April 30 – Emperor Galerius declares on his deathbed religious freedom, and issues his Edict of Toleration, ending persecution of Christians in the Eastern part of the Roman Empire.
- May 5 – Galerius dies, age 51, from a gruesome disease, possibly bowel cancer or Fournier gangrene.
- Maximinus Daza and Licinius divide the Eastern Empire between themselves.
- Maximinus recommences the persecution of Christians, having encouraged his subjects to petition him to do so.
- Fearing an alliance between Licinius and Constantine I, Maximinus forges a secret alliance with Emperor Maxentius.
- July 13 – Huai of Jin, emperor of the Jin Dynasty, is captured at Luoyang. The capital city is pillaged by Liu Cong, ruler of the Xiongnu state; the invaders slaughter 30,000 citizens.
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- November 25 – Peter I, patriarch of Alexandria
- December 3 – Diocletian, Roman emperor (b. 244)
- Domitius Alexander, Roman emperor and usuper
- Gaius Galerius Valerius Maximianus, Roman emperor
- Gou Xi (or Daojiang), Chinese inspector and general
- Sima Yue (or Yuanchao), Chinese prince and regent
- Wang Mi (or Zigu), Chinese general and rebel leader
- Wang Yan, Chinese official and politician (b. 256)