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Emperor Lothair I divides Middle Francia between his three sons (Treaty of Prüm).

Events

November 20 – Theoktistos, co-regent of the Empire on behalf of 15-year old Emperor Michael III, is murdered on the orders of Michael.

September 29 – Emperor Lothair I dies after a 15-year reign (co-ruling with his father Louis the Pious until 840). He divides the Middle Frankish Kingdom between his three sons in an agreement called the Treaty of Prüm—the eldest, Louis II, receives the northern half of Italy and the title of Holy Roman Emperor. The second, Lothair II, receives Lotharingia (the Low Countries and Upper Burgundy). The youngest, Charles, receives Lower Burgundy and Provence.

Spring – King Æthelwulf of Wessex decides to go on a pilgrimage to Rome, accompanied by his youngest son Alfred (age 6) and a large retinue.Template:Sfn He divides the kingdom between his two eldest sons; Æthelbald receives the western part of Wessex, while Æthelberht becomes ruler over Kent, Surrey, Sussex and Essex.<ref>Paul Hill (2009). The Viking Wars of Alfred the Great, p. 17. Template:ISBN</ref>

Caliph al-Mutawakkil sends an Abbasid army, led by the Turkic general Bugha al-Kabir, to suppress an uprising of rebellious Armenian nakharars. He subdues the country, and deports many Armenian nobles to the caliphal capital of Samarra.Template:Sfn

July 17 – Pope Leo IV dies after an 8-year reign, and is succeeded by Benedict III as the 104th pope of Rome. Anastasius is made anti-pope by Lothair I.
Æthelwulf grants churches in Wessex the right to receive tithes. He gives one-tenth of his lands to the Church.Template:Sfn
The Slavic alphabet is created by Saints Cyril and Methodius.