1091

1091 (MXCI) was a common year starting on Wednesday of the Julian calendar, the 1091st year of the Common Era (CE) and Anno Domini (AD) designations, the 91st year of the 2nd millennium, the 91st year of the 11th century, and the 2nd year of the 1090s decade. As of the start of 1091, the Gregorian calendar was 6 days ahead of the Julian calendar, which was the dominant calendar of the time.

Millennium:	2nd millennium
Centuries:	10th century – 11th century – 12th century
Decades:	1060s  1070s  1080s  – 1090s –  1100s  1110s  1120s
Years:	1088 1089 1090 – 1091 – 1092 1093 1094

Roger I of Sicily (r. 1071–1101)

Europe

• King William II of England invades Normandy.
• Ladislaus I of Hungary occupies Slavonia.
• King Stjepan II of Croatia, the last member of the Trpimirović dynasty, died without leaving anyone to inherit his thrown and title.

British Isles

• October 17 – London Tornado of 1091: A T8/F4 tornado is recorded in St Mary-le-Bow of London, England; the storm destroys London Bridge.
• Henry, the third son of William the Conqueror, is forced to give up his property of Cotentin in Normandy after his two older brothers, William Rufus and Robert Curthose, make a peace agreement.
• King Malcolm III of Scotland makes an unsuccessful attempt to invade English territory, but is finally forced to give a public statement of allegiance to King William II of England.
• Cardiff Castle is built.

Mediterranean

• April 29 – Battle of Levounion: The Pechenegs surround and attack Constantinople, but are defeated so completely by Emperor Alexius I that they are completely eliminated.
• February; With the taking of Noto, the Normans complete the 30 year long takeover of Sicily from the Islamic rulers.
• The Islamic Abbadid dynasty ruling in Spain falls when the Almoravids storm Seville. Faced with this new threat, the king of Badajoz, al-Mutawakkil ibn al-Aftas, got the support of Castile in exchange for the Muslim positions on the Tagus river — Sintra, Santarém and Lisbon.
• Roger Guiscard takes Malta.

Religion

• Athanasius VI bar Khamoro becomes Syriac Orthodox Patriarch of Antioch.

Deaths

• June 17 – Dirk V, Count of Holland
• July 5 – Abbot William of Hirsau
• August 25 – Sisnando Davides, military leader
• December 19 – Adelaide of Susa, margravine of Turin
• date unknown –

Robert D'Oyly, first Lord of Oxford Castle