840
| Years: 836 837 838 839 - 840 - 841 842 843 844 | |
| Decades: 810s 820s 830s - 840s - 850s 860s 870s | |
| Centuries: 8th century - 9th century - 10th century | |
Events
- After the death of Louis the Pious, his sons Lothar, Charles the Bald and Louis the German fight over the division of the empire, with Lothar succeding as Emperor.
- Tang Wu Zong succeeds Tang Wen Zong as emperor of China.
- Foundation of Dublin by Vikings.
Births
- Aed I of Scotland (approximate date) (d. 878)
- Edmund of East Anglia (approximate date) (d. 870)
Deaths
- June 20 - Louis the Pious, King of the Franks, Emperor of the Holy Roman Empire (b. 778)
- Emperor Junna, emperor of Japan (b. 786)af:840
ast:840 bg:840 bs:840 ca:840 cs:840 da:840 de:840 el:840 es:840 eo:840 eu:840 fr:840 ko:840년 hr:840 io:840 it:840 lb:840 hu:840 mk:840 nl:840 no:840 nn:840 pl:840 pt:840 ro:840 ru:840 sk:840 sl:840 sr:840 fi:840 sv:840 tt:840 tr:840 uk:840 zh:840年