|311 by topic|
|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
|Wikimedia Commons has media related to 311.|
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.
- 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 – Emperor Galerius dies, age 51, from a gruesome disease, possibly bowel cancer or Fournier gangrene.
- Maximinus II divides the Eastern Empire between co-emperor Licinius, and mobilises his army for a campaign in Asia Minor. He recommences the persecution of Christians.
- Maxentius, Roman usurper, reconquers the African provinces from Domitius Alexander.
- Maxentius builds the Circus of Maxentius near the Via Appia. The circus is 513 meters long and 91 meters wide, and offers an accommodation to some 10,000 people.
- December 3 – Diocletianus dies at his palace in Split (Croatia). Possibly he commits suicide.
- Jin Huaidi, emperor of the Jin Dynasty, is captured at Luoyang. The capital city is pillaged by Liu Cong, ruler of the Xiongnu state (Huns), the invaders slaughter 30,000 citizens.
- July 2 – Pope Miltiades succeeds Pope Eusebius as the 32nd pope.
- The Donatist schism occurs in the African church.
- November 25 – Saint Peter, Patriarch of Alexandria (martyred)
- December 3 – Gaius Aurelius Valerius Diocletianus, Roman Emperor (b. 244)
- Domitius Alexander, Roman usuper (approximate date)
- Gaius Galerius Valerius Maximianus, Roman emperor (b. 260)
- Sima Yue, prince and regent of the Jin Dynasty