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Events

Battle of Cephalonia: A Byzantine fleet, under Admiral Nasar, is sent by Emperor Basil I to the Ionian Islands. Nasar defeats the Aghlabids in a night battle near Cephalonia (modern Greece).
May 1 – The Nea Ekklesia is inaugurated in Constantinople, by Patriarch Photius I, setting the model for all later cross-in-square Orthodox churches.<ref name=Mango194>Mango (1986), p. 194.</ref>Template:Full citation needed<ref name="Ousterhout34">Ousterhout (2007), p. 34.</ref>Template:Full citation needed

February 2 – Battle of Lüneburg Heath: King Louis III is defeated by the Norse Great Heathen Army at Lüneburg Heath. The Saxons are routed in a snowstorm; many drown in the river or are captured during the retreat.
Battle of Thimeon: King Louis III ("the Younger") defeats Vikings (probably Norsemen) from England, near Charleroi, north of the River Sambre. During the battle 5,000 Vikings are killed.
Battle of Fjaler: King Harald Fairhair moves east along the Norwegian coast with his fleet. He defeats his rival Atle Mjove at Fjaler in Sunnfjord, and lands with his longships at Tønsberg.
December – Treaty of Ribemont: Louis the Younger and the kings of the West Frankish Kingdom sign a treaty. The young Frankish monarch, Louis III, is reduced to merely Neustria.
Lambert I, duke of Spoleto, dies while besieging the city of Capua. He is succeeded by his son Guy II.
The oldest known mention is made of the city of Dortmund (approximate date).

Fujiwara no Mototsune, Japanese statesman, creates the position of regent (kampaku) for himself. The Fujiwara clan will be able to dominate the government for more than 3 centuries.
December 22 – Luoyang, eastern Chinese capital of the Dynasty, is captured by rebel leader Huang Chao, during the reign of emperor Xi Zong.

Pope John VIII issues the bull Industriae Tuae, creating an independent ecclesiastical province in Great Moravia, with archbishop Methodius as its head. Old Church Slavonic is recognized as the fourth liturgical language, besides Latin, Greek and Hebrew.
The first known Christian bishopric in Slovakia is established in the city of Nitra, with Wiching as bishop.