Editing 837 (section)

== Events ==
<onlyinclude>

=== By place ===
==== Byzantine Empire ====
* [[Byzantine–Arab wars (780–1180)#Period of 780–842|Byzantine–Arab War]]: Emperor [[Theophilos (emperor)|Theophilos]] leads a massive Byzantine expeditionary force into [[Mesopotamia]]. He sacks the cities [[Arsamosata]] and [[Sack of Amorium#Background|Sozopetra]] — which some sources claim as the birthplace of [[Abbasid Caliphate|Abbasid]] caliph [[Al-Mu'tasim]] — and forces [[Malatya|Melitene]] to pay [[tribute]].<ref name="Treadgold440">{{A History of the Byzantine State and Society|page=440}}</ref>
* The [[Slavs]] in the vicinity of [[Thessaloniki]] revolt against the [[Byzantine Empire]]. Theophilos undertakes an [[Forced migration|evacuation]] of some Byzantine captives, who are settled in trans-[[Danube|Danubian]] [[Bulgaria]].

==== Europe ====
* [[Presian I of Bulgaria|Presian I]], ruler (''[[Khan (title)|khan]]'') of the [[First Bulgarian Empire|Bulgarian Empire]], sends his prime-minister [[Isbul]] against the [[Smolyani]] (a Slavic tribe in Byzantine territory near the [[Struma (river)|Struma River]]). The Bulgarian army campaigns along the [[Aegean Sea|Aegean]] coasts, and conquers most of [[Thrace]] and [[Macedonia (region)|Macedonia]], including the fortress city of [[Philippi]], as recorded in the [[Presian Inscription]].<ref>{{The Early Medieval Balkans|page=109}}</ref>
* The city of [[Naples]] (modern [[Italy]]) is attacked by [[Saracen]]s from [[Egypt]] demanding an annual payment (approximate date).

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

=== By topic ===
==== Astronomy ====
* [[April 10]] &ndash; [[Halley's Comet]] passes approximately [[1 E9 m|5 million km]] from [[Earth]], its closest ever approach.</onlyinclude>