Editing 821 (section)

== Events ==
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=== By place ===

==== Byzantine Empire ====
* Byzantine general [[Thomas the Slav]] leads a revolt, and secures control over most of the Byzantine [[Theme (Byzantine district)|themes]] (provinces) in [[Anatolia]]. He gets recognition from the [[Abbasid Caliphate]], and concludes a [[peace treaty]] with Caliph [[al-Ma'mun]]. Thomas crosses with his fleet from [[Abydos (Hellespont)|Abydos]] to [[Thrace]], and blockades Emperor [[Michael II]] in [[Constantinople]]; but Thomas' first attack on the capital fails.

==== Europe ====
* [[February]] &ndash; Duke [[Borna of Croatia]] dies after an 11-year reign, as [[vassal]] of the [[Francia|Frankish Empire]]. He is succeeded by his nephew, [[Vladislav of Croatia|Vladislav]].<ref name="Mladjov">{{cite web | last = Mladjov | first = Ian | title = Croatian Rulers | url = http://sitemaker.umich.edu/mladjov/files/croatian_rulers.pdf | access-date = 2011-05-21 }}{{Dead link|date=May 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Emperor [[Louis I the Pious|Louis I]] recognizes him as prince of [[Dalmatia]] and [[Liburnia]], at the [[Council of Aachen (821)|Council of Aachen]].
* [[October]] &ndash; [[Lothair I]], co-emperor and eldest son of Louis I, marries [[Ermengarde of Tours|Ermengarde]] in [[Thionville]] (northeastern [[France]]). She is the daughter of Count [[Hugh of Tours]].

==== Britain ====
* King [[Coenwulf of Mercia]] dies in [[Basingwerk Abbey|Basingwerk]] near [[Holywell, Flintshire|Holywell]] ([[Wales]]), while preparing for another assault on [[Powys]], and is buried in [[Winchcombe Abbey]]. He is briefly succeeded by his son [[Saint Kenelm|Cynehelm]], but he is killed, probably fighting the Welsh, though supposedly through the treachery of his sister [[Cwenthryth]]. The [[Mercia]]n throne passes to Coenwulf's brother, [[Ceolwulf I of Mercia|Ceolwulf I]].

==== Abbasid Caliphate ====
* By the time [[Al-Ma'mun]] became caliph, the Arabs and the Byzantines had settled down into border skirmishing, with Arab raids deep into [[Anatolia]] to capture booty.
* [[Tahir ibn Husayn]], an [[Iranian peoples|Iranian]] general, is appointed as governor of [[Greater Khorasan|Khurasan]], as a reward for supporting the [[Abbasid Caliphate|Abbasid]] caliph [[al-Ma'mun]] in the [[Fourth Fitna]]. 
* Caliph Al-Ma'mun appointed [[Nu'aym ibn al-Waddah al-Azdi]] as the governor of Yemen in 821.
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