|313 by topic|
|Ab urbe condita||1066|
|Chinese calendar||壬申年 (Water Monkey)
3009 or 2949
— to —
癸酉年 (Water Rooster)
3010 or 2950
|- Vikram Samvat||369–370|
|- Shaka Samvat||234–235|
|- Kali Yuga||3413–3414|
|Iranian calendar||309 BP – 308 BP|
|Islamic calendar||319 BH – 318 BH|
|Minguo calendar||1599 before ROC
|Seleucid era||624/625 AG|
|Thai solar calendar||855–856|
|Wikimedia Commons has media related to 313.|
Year 313 (CCCXIII) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantinus and Licinianus (or, less frequently, year 1066 Ab urbe condita). The denomination 313 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. This year is notable for ending of the persecution of Christians in the Roman Empire.
- February 3 – Edict of Milan: Constantine the Great and co-emperor Licinius meet at a conference in Mediolanum (modern Milan). They proclaim a policy of religious freedom for all, ending the persecution of Christians in the Roman Empire and returning property confiscated from Christians. 
- Emperor Maximinus II crosses the Bosphorus with an army of 70,000 men and lays siege to Heraclea (Turkey). He captures the city after eight days.
- April 30 – Battle of Tzirallum: Licinius defeats his rival Maximinus II and becomes Emperor of the Eastern Roman Empire. Maximinus flees to Nicomedia and commits suicide.
- March 14 – Emperor Jin Huidi is executed by Liu Cong, ruler of the Xiongnu state (Han Zhao). At the imperial new year he and a number of former Jin officials are poisoned. Crown prince Jin Mindi, age 13, succeeds in Chang'an his uncle Jin Huidi and becomes the new emperor of the Jin dynasty.
- Nintoku, the fourth son of Ōjin, becomes the 16th emperor of Japan.
- Basilica of Maxentius and Constantine (Basilica Nova), Rome, is finished.
- February 3 – Edict of Milan: Constantine the Great and co-emperor Licinius meet at a conference in Mediolanum (modern Milan). They proclaim a policy of religious freedom for all, ending the persecution of Christians in the Roman Empire and returning property confiscated from Christians.
- October 2 – Lateran Synod: Donatism is declared a heresy.
- Arius preaches of the human nature of Jesus.
- Didymus the Blind, Alexandrian theologian (approximate date)
- Shi Hong, emperor of the Chinese Jie state (d. 334)
- March 14 – Jin Huidi, Chinese emperor of the Jin dynasty (b. 284)
- June – Pope Achillas of Alexandria
- August – Maximinus II, Roman emperor (b. 270)
- Dowager Zhang, empress of the Xiongnu state (Han Zhao)
- Zhang Huiguang, empress of the Xiongnu state (Han Zhao)
- Frend, W. H. C. The Early Church SPCK 1965, p. 137