1081

By place

Byzantine Empire

• April 1 - Emperor Nikephoros III is forced to abdicate the throne, and retires to the Peribleptos monastery. He is succeeded by Alexios I Komnenos, who is crowned on April 5, as ruler of the Byzantine Empire. His brother-in-law Nikephoros Melissenos supports Alexios as new emperor, in exchange for the title of Caesar, and is appointed as commander of the Byzantine armies in the West.
• May - A Norman fleet of 150 ships, led by Duke Robert Guiscard, sets off towards the Dalmatian coast. An army of 15,000 men sails to city of Avalona ; they are joined by several ships from Ragusa, a republic in the Balkans who are enemies of the Byzantines.
• October 18 - Battle of Dyrrhachium: After taking the island of Corfu, Robert Guiscard advances to Dyrrhachium, and lays siege to the city. Alexios I Komnenos supports defend Illyria from the Normans, but is defeated by Guiscard, outside Dyrrhachium, the Byzantine capital city of Illyria.

  Europe

• King Alfonso VI of Castile exiles his most famous commander, Rodrigo Díaz de Vivar, who goes into exile and offers his services to the twins – Counts Ramon Berenguer II and Berenguer Ramon II of Barcelona, but is turned down. He ends up in the service of Emir Yusuf al-Mu'taman ibn Hud of Zaragoza.
• King Mihailo dies after a 30-year reign. He is succeeded by his son, Constantine Bodin as ruler of Duklja.

  England

• Battle of Mynydd Carn : Gruffudd ap Cynan in alliance with Rhys ap Tewdwr, prince of Deheubarth, defeats the forces of Trahaearn ap Caradog, Caradog ap Gruffydd and Meilir ap Rhiwallon, allowing Gruffudd to claim the Kingdom of Gwynedd.
• King William I orders the creation of a castle at Cardiff during his tour of southern Wales. The first castle on the site would be a motte and bailey type and is built on existing Roman fortifications.

  Seljuk Empire

• Seljuk emir Tzachas conquers Smyrna and founds a short-lived independent state, which emerges as the first sea power in Turkish history.

  By topic

Religion

• Pope Gregory VII writes a letter to Hermann, bishop of Metz, about the behavior of Emperor Henry IV.
• Construction begins on St. Canute's Cathedral in Odense.