830s

Britain

• King Wiglaf of Mercia regains control from Wessex, and returns to the throne.^[1]

Byzantine Empire

• June 5 – 16-year-old Emperor Theophilos marries the Armenian noblewoman Theodora, in the Hagia Sophia at Constantinople. He chooses her during a representation of a bride-show; she becomes empress (Augusta) of the Byzantine Empire.
• Byzantine–Arab War: Muslim reinforcements from Ifriqiya and Al-Andalus (modern Spain) defeat Byzantine forces under Theodotus in Sicily, but a plague once again compels them to retreat to Mazara del Vallo, and evacuate to North Africa.

Europe

• Emperor Louis the Pious returns from a campaign in Brittany, and is captured by his son Pepin I, king of Aquitaine. He is put under house arrest at Compiegne, and his wife Judith is incarcerated at Poitiers.

North Africa

• The Ad-dimnah Hospital (bimaristan) is created in Kairouan (modern Tunisia), by the Aghlabid emir Ziyadat Allah I.^[2]

Religion

• Nennius, Welsh abbot of Bangor Fawr, compiles the Historia Brittonum. He is also known for the Historia's list of the 12 battles of King Arthur (approximate date).
• Hirsau Abbey (modern Germany) is founded by the Rhenish Franconian count Erlafried of Calw (approximate date).
• Ansgar, a Frankish missionary, visits the trade city Birka, located at Lake Mälaren in Sweden (approximate date).

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