837

• Byzantine–Arab War: Emperor Theophilos leads a massive Byzantine expeditionary force into Mesopotamia. He sacks the cities Arsamosata and Sozopetra — which some sources claim as the birthplace of Abbasid caliph Al-Mu'tasim — and forces Melitene to pay tribute.{{A History of the Byzantine State and Society|page=440}}
• The Slavs in the vicinity of Thessaloniki revolt against the Byzantine Empire. Theophilos undertakes an evacuation of some Byzantine captives, who are settled in trans-Danubian Bulgaria.

• Presian I, ruler (khan) of the Bulgarian Empire, sends his prime-minister Isbul against the Smolyani (a Slavic tribe in Byzantine territory near the Struma River). The Bulgarian army campaigns along the Aegean coasts, and conquers most of Thrace and Macedonia, including the fortress city of Philippi, as recorded in the Presian Inscription.{{The Early Medieval Balkans|page=109}}
• The city of Naples (modern Italy) is attacked by Saracens from Egypt demanding an annual payment (approximate date).

• King Drest IX dies after a 3-year reign. He is succeeded as ruler of the Picts by his cousin Eóganan mac Óengusa.

• April 10 – Halley's Comet passes approximately 5 million km from Earth, its closest ever approach.

• Al-Muntasir, Muslim caliph (d. 862)
• Baldwin I, margrave of Flanders (approximate date)
• Ibn Duraid, Muslim poet and philologist (d. 933)
• Ibn Khuzaymah, Muslim hadith and scholar (d. 923)

• Antony I, patriarch of Constantinople
• Drest IX, king of the Picts
• Eadwulf, bishop of Lindsey
• Giovanni I, doge of Venice
• Hugh of Tours, Frankish nobleman
• Li Zaiyi, general of the Tang Dynasty (b. 788)
• Maxentius, patriarch of Aquileia
• Oliba I, Frankish nobleman
• Peter of Atroa, Byzantine abbot (b. 773)

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