830

By place

Britain

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

Byzantine Empire

• June 5 - Emperor Theophilos, 16, marries the Armenian noblewoman Theodora, in the Hagia Sophia at Constantinople. He chooses her during a representation of a bride-show; she becomes empress of the Byzantine Empire.
• Byzantine–Arab War: Muslim reinforcements from Ifriqiya and Al-Andalus 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 is created in Kairouan, by the Aghlabid emir Ziyadat Allah I.

South Asia

• About 830 an Arabian dhow sinks on its journey from China to Arabia near the Indonesian island of Belitung, carrying some 60,000 trade items, the largest collection of Tang dynasty artifacts outside of China.

By topic

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.
• Hirsau Abbey is founded by the Rhenish Franconian count Erlafried of Calw.
• Ansgar, a Frankish missionary, visits the trade city Birka, located at Lake Mälaren in Sweden.