866
# 866

Year 866 (DCCCLXVI) was a common year starting on Tuesday (link will display the full calendar) 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.

**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 (Upper Mesopotamia), which will last for 30 years.

**Japan**

* Fujiwara no Yoshifusa becomes regent (sesshō) to assist the child emperor Seiwa, starting the Fujiwara regency.

### By topic

**Religion**

* Boris I, ruler (knyaz) 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 (approximate date).

## Births

* June 10 – Uda, emperor of Japan (d. 931)
* September 19 – Leo VI, Byzantine emperor (d. 912)
* Carloman II, king of the West Frankish Kingdom (approximate date)
* Robert I, king of the West Frankish Kingdom (d. 923)
* Yao Yi, chancellor of Later Tang (d. 940)

## Deaths

* April 21 – Bardas, Byzantine chief minister and regent
* May 27 – Ordoño I, king of Asturias
* June 21 – Rodulf, Frankish archbishop
* July 2 – Robert the Strong, Frankish nobleman
* July 16 – Irmgard, Frankish abbess
* October 17 – Al-Musta'in, Abbasid caliph
* Adelaide of Tours, Frankish noblewoman
* Al-Mu'ayyad, Abbasid prince
* Charles the Child, king of Aquitaine
* Eberhard, duke of Friuli
* Emenon, Frankish nobleman
* Hungerus Frisus, bishop of Utrecht
* Linji Yixuan, Chinese monk and founder of the Linji school
* Liudolf, duke of Saxony
* Ranulf I, Frankish nobleman (b. 820)
* Robert, Frankish nobleman (b. 834)
* Rudolph, Frankish nobleman
* Wang Shaoyi, general of the Tang Dynasty
* Yahya ibn Yahya, Idrisid emir of Morocco
