866
Year 866 was a common year starting on Tuesday of the Julian calendar.
Events
By place
Byzantine Empire
- April 21 - Bardas, the regent of the Byzantine Empire, is murdered by Basil the Macedonian at Miletus, while conducting a large-scale expedition against the Saracen stronghold of Crete.
- May 26 - Basil the Macedonian is crowned co-emperor of the Byzantine Empire, and is adopted by the much younger Michael III.
Europe
- May 27 - King Ordoño I, ruler of the Kingdom of Asturias, dies after a 16-year reign. He is succeeded by his son, Alfonso III, who later is referred to as "Alfonso the Great".
- July 2 - Battle of Brissarthe: Frankish forces, led by Robert the Strong, are defeated by a joint Breton-Viking army.
- Louis II, Holy Roman Emperor, defeats the Saracen invaders who are ravaging southern Italy.
Britain
- The Great Heathen Army of the Vikings rides north to Northumbria. The Northumbrians are preoccupied with a civil war, and the Danes enter York unopposed.
Italy
- An army in Lucera is assembled by orders of Louis II in preparation for an attack on the Emirate of Bari.
Abbasid Caliphate
- October 17 - Caliph al-Musta'in is put to death, after a 4-year reign. He is succeeded by al-Mu'tazz, who becomes the youngest Abbasid caliph to assume power.
- The Kharijite revolt against the Abbasid Caliphate begins in Al-Jazira, which will last for 30 years.
Japan
- Fujiwara no Yoshifusa becomes regent to assist the child emperor Seiwa, starting the Fujiwara regency.
By topic
Religion
- Boris I, ruler of the Bulgarian Empire, sends a diplomatic mission, led by the Bulgarian nobleman Peter, to Rome, in an effort to renew ties with the West.
- Pope Nicholas I orders that all Catholics should abstain from eating the "flesh, blood, or marrow" of warm-blooded animals on Wednesdays and Fridays.
- Pope Nicholas I forbids the use of torture in prosecutions for witchcraft.