1091

By place

Byzantine Empire

• Spring - Tzachas, a Seljuk Turkish military commander, establishes an independent maritime state centred in the Ionian coastal city of Smyrna. He proclaims himself emperor, and concludes an alliance with the Pechenegs in Thrace. Tzachas uses his fleet to blockade Constantinople by sea, while the Pechenegs besiege the capital by land.
• April 29 - Battle of Levounion: Emperor Alexios I supported by his allies defeats the Pechenegs' 80,000 men at the Evros River near Enos. The Cumans and Byzantine forces fall upon the enemy camp, slaughtering all in their path. The Pechenegs are butchered so savagely, that they are almost wiped out.

  Europe

• Spring - King Stephen II, the last member of the Trpimirović Dynasty, dies without leaving an heir after a 2-year reign. War and unrest breaks out in Croatia afterwards. King Ladislaus I of Hungary, on instigation of his sister, Queen Helena, intervenes in the conflict and occupies Croatia. He proclaims himself king, but is contested by the Croatian nobleman Petar Snačić.
• February - Norman conquest of Sicily: The Normans conquer Noto and complete the 30-year-long conquest of Sicily from the Moorish rulers. Duke Roger Borsa surrenders his share in the castles of Calabria, and receives his inheritance of Palermo. He grants charters to various towns and encourages urban planning in Apulia and Calabria.
• Summer - The Norman invasion of Malta: A Norman fleet led by Count Roger I arrives in Malta. Roger disembarks his army, and besieges the island's capital Medina. The inhabitants negotiate peace terms and swear an oath of loyalty to Roger. On the way back, the Normans sack the island Gozo.
• July - The Abbadid Dynasty ruling in Al-Andalus falls, when the Almoravid forces storm Seville. Confronted with this threat, Emir Muhammad ibn Abu Bakr Muhammad al-Aftas of Badajoz obtains the support of King Alfonso VI of Castile, in exchange for the Moorish positions on the Tagus River.

  England

• Spring - King William II invades Normandy with a large army. His brothers, Henry and Robert Curthose, mobilizes mercenary forces to resist William during the siege at Mont-Saint-Michel. Henry is forced to surrender his estates of the Cotentin Peninsula in Normandy and signs a peace treaty.
• Summer - King Malcolm III of Scotland invades the north of England, and besieges Durham. The Normans led by William II marches north to oppose the Scots, but a conflict is averted. Malcolm is forced to accept the terms of the Treaty of Abernethy and pays homage to William.
• Cardiff Castle is constructed by Robert Fitzhamon, Norman lord of Gloucester.

  By topic

Disasters

• October 17 - London tornado: A T8 tornado occurs in London. The wooden London Bridge is demolished and the church of St. Mary-le-Bow is badly damaged.

  Religion

• December - Athanasius VI bar Khamoro becomes patriarch and head of the Syriac Orthodox Church in Antioch.