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 Holy Roman Empire, with Lothar succeeding as Emperor.
- Tang Wu Zong succeeds Tang Wen Zong as emperor of China.
- Foundation of Dublin by Vikings.
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
am:840 እ.ኤ.አ. ar:840 an:840 ast:840 az:840 bn:৮৪০ bpy:মারি ৮৪০ bs:840 bg:840 ca:840 cv:840 cs:840 co:840 da:840 de:840 et:840 el:840 es:840 eo:840 eu:840 fr:840 ko:840년 hr:840 io:840 id:840 is:840 it:840 ka:840 ht:840 (almanak jilyen) la:840 lb:840 lmo:840 hu:840 mk:840 ms:840 nl:840 ja:840年 nap:840 no:840 nn:840 oc:840 pl:840 pt:840 ksh:Joohr 840 ro:840 ru:840 год sq:840 ru-sib:840 scn:840 sk:840 sl:840 sr:840 fi:840 sv:840 tt:840 th:พ.ศ. 1383 tr:840 uk:840 uz:840 vec:840 zh:840年