842

By place

Byzantine Empire

• January 20 - Emperor Theophilos dies of dysentery at Constantinople, after a 12-year reign in which he expended much effort defending the eastern frontier against the invading Muslim Arabs. Theophilos is succeeded by his 2-year-old son Michael III, with his mother Theodora as regent and the 'temporary' sole ruler of the Byzantine Empire.
• February 19 - The Medieval Iconoclastic Controversy ends as a council in Constantinople formally reinstates the veneration of icons in the churches.

  Europe

• February 14 - Oaths of Strasbourg: King Louis the German, ruler of East Francia, and his half-brother Charles the Bald, ruler of West Francia, meet with their armies at Strasbourg. They agree to swear allegiance to each other, and to support each other against their brother Lothair I.
• March 20 - King Alfonso II of Asturias dies after a 50-year reign, in which he undertook numerous campaigns against the Muslim armies of the Umayyad Emirate of Córdoba, and allied himself with the late Charlemagne. The childless Alfonso chooses Ramiro I, son of former king Bermudo I, as his successor.

  Britain

• Uurad of the Picts dies after a 3-year reign, and is succeeded by his son Bridei VI, who contests his power with rival groups, led by Bruide son of Fokel and Kenneth MacAlpin.
• Vikings attack the Irish monastery at Clonmacnoise from bases in Ireland.

  Abbasid Caliphate

• January 5 - Caliph Al-Mu'tasim dies at Samarra, after an 8-year reign. He is succeeded by his son Al-Wathiq, as ruler of the Abbasid Caliphate.