840s

The 840s decade ran from January 1, 840, to December 31, 849.

Significant people

 * Al-Mu'tasim
 * Al-Wathiq
 * Alfred the Great
 * Louis the Pious
 * Charles the Bald
 * Ermentrude of Orléans
 * Louis the Stammerer
 * Louis the German
 * Lothair I
 * Kenneth I of Scotland
 * Ragnar Lodbrok
 * Michael III