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|Ab urbe condita||1071|
|Balinese saka calendar||239–240|
|Chinese calendar||丁丑年 (Fire Ox)|
3014 or 2954
— to —
戊寅年 (Earth Tiger)
3015 or 2955
|- Vikram Samvat||374–375|
|- Shaka Samvat||239–240|
|- Kali Yuga||3418–3419|
|Iranian calendar||304 BP – 303 BP|
|Islamic calendar||313 BH – 312 BH|
|Minguo calendar||1594 before ROC|
|Seleucid era||629/630 AG|
|Thai solar calendar||860–861|
444 or 63 or −709
— to —
445 or 64 or −708
Year 318 (CCCXVIII) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Licinianus and Crispus (or, less frequently, year 1071 Ab urbe condita). The denomination 318 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.
- Emperor Constantine the Great gives the ancient Roman town Drepana (Asia Minor) the name Helenopolis, after his mother Helena, and builds a church in honour of the martyr St. Lucian.
- Emperor Constantine the Great is given the title Brittanicus Maximus, for successful engagements in Britain (the details of which are unknown).
- The Chinese Empire loses its territories to the north of the Yangtze River, to the benefit of the Xiongnu and the Xianbei. The Former Zhao state is proclaimed; Liu Can and the state ruling family at Pingyang are executed in a coup d'état by Jin Zhun, who is in turn overthrown by Shi Le and Liu Yao.
- Liu Yao becomes the new emperor of Han Zhao and moves his capital to Chang'an.
- February 7 – Jin Mindi, emperor of the Jin Dynasty (murdered) (b. 300)
- August 31 – Liu Cong, emperor of the Xiongnu state
- Fan Changsheng, Chinese taoist
- Jin Zhun, official of the Xiongnu state Han Zhao
- Liu Can, emperor of the Xiongnu state