856

Rabanus Maurus (left) presents his work to archbishop Odgar of Mainz (right)

Events

March 15 – Emperor Michael III overthrows the regency of his mother Theodora. He appoints his uncle Bardas as the de facto regent and co-ruler of the Byzantine Empire.<ref name="Treadgold450-1">Template:Harvnb.</ref>

King Charles the Bald cedes the county of Maine to Erispoe, ruler (duke) of Brittany—this in return for an alliance against the Vikings.
King Ordoño I of Asturias is said to have begun the repopulation of the town of León in the northwest of Spain (approximate date).

October 1 – King Æthelwulf of Wessex marries the 12- or 13-year-old Judith, daughter of Charles the Bald, at Verberie (Northern France). She is crowned queen and anointed by Hincmar, archbishop of Reims. The marriage is a diplomatic alliance between Wessex and the West Frankish Kingdom.<ref>Paul Hill (2009). The Viking Wars of Alfred the Great, p. 18. Template:ISBN.</ref>
Winter – Æthelwulf returns to Wessex to face a revolt by his eldest son Æthelbald, who usurps the throne. Æthelwulf agrees to give up the western part of his kingdom, in order to avoid a civil war. He keeps control over Sussex, Surrey, Essex and Kent, over which Prince Æthelberht has presided.Template:Sfnm

November (approximate date) – An earthquake in Corinth, Greece kills an estimated 45,000 people.
December 3 – Another earthquake strikes the Abbasid Caliphate (modern-day Tunisia), also killing an estimated 45,000 people.
December 22 – Another earthquake strikes Damghan (modern-day Iran), killing an estimated 200,000 people.