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 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,