1240 was a leap year.
|Centuries:||12th century – 13th century – 14th century|
|Decades:||1210s 1220s 1230s – 1240s – 1250s 1260s 1270s|
|Years:||1237 1238 1239 – 1240 – 1241 1242 1243|
- Batu Khan and the Golden Horde sack the Ruthenian city of Kiev.
- Mandinka prince Sundiata Keita defeats Sosso king Soumaoro Kanté at the Battle of Kirina, beginning the Mali Empire.
- July 15 – Russian prince Alexander Nevsky defeats the Swedes in the Battle of the Neva, saving Russia from a full-scale enemy invasion from the North.
- End of the civil war era in Norway.
- Saint Maurice is started to be portrayed as Moor.