|Covid-19|Byzantine–Arab War: Emperor Theophilos leads a Byzantine expeditionary force (70,000 men) 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.
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 (see Presian Inscription).
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 by his cousin Eóganan, as ruler of the Picts.
April 10 – Comet Halley 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)
Year 837 (DCCCXXXVII) was a common year starting on Monday (link will display the full calendar) of the Julian calendar.