|Covid-19|February 26 – Battle of Benevento: The army of Charles, Count of Anjou, defeats a combined German and Sicilian force led by King Manfred of Sicily. Manfred is killed in the battle and Pope Clement IV invests Charles as king of Sicily and Naples.
July – Mary de Ferrers is ordered to surrender land and Liverpool Castle to Edmund, second son of Henry III.
October – In England, the Second Barons' War winds down as supporters of the slain rebel leader Simon de Montfort make an offer of peace to the king in the Dictum of Kenilworth; after slight modifications to the peace settlement, it is agreed to the following year.
The war between Scotland and Norway ends as King Alexander III of Scotland and King Magnus VI of Norway agree to the Treaty of Perth, which cedes the Western Isles and Isle of Man to Scotland in exchange for a large monetary payment.
Niccolo and Maffeo Polo, father and uncle of Marco Polo, reach Kublai Khan's capital Khanbaliq (now Beijing) in China, setting the stage for Marco's famous expedition 5 years later. Kublai Khan sends the Polos back with a message requesting that the Pope dispatch western scholars to teach in the Mongol Empire; however, this request is largely ignored.
The Mamluk sultan Baibars expands his domain, capturing the city of Byblos (in present-day Lebanon) and the important castle of Toron from the crusader states, and defeating the Armenians at Cilicia.
In France, the gold écu and silver grosh coins are minted for the first time.
Ode de Pougy, Abbess of Notre Dame aux Nonnains, sends a gang to attempt to destroy the nearly-completed Church of St Urbain, Troyes.
Hethum II of Armenia (d. 1307)
Hedwig of Kalisz, queen consort of Poland (d. 1339)
John of Brittany, Earl of Richmond (d. 1334)
Beatrice Portinari, Dante Alighieri's beloved and guide through Heaven in The Divine Comedy (d. 1290)
Margaret of Villehardouin, Lady of Akova (d. 1315)
Rigdzin Kumaradza, Buddhist master (d. 1343)
Zhou Daguan, diplomat and geographer (d. 1346)
Duns Scotus, philosopher (approximate date; d. 1308)
January 11 – Swietopelk II, Duke of Pomerania
February 26 – Manfred, King of Sicily (b. 1232)
June 12 – Henry II, Prince of Anhalt-Aschersleben (b. 1215)
August 4 – Eudes of Burgundy, Count of Nevers (b. 1230)
September 20 – Jan Prandota, Bishop of Kraków
October 21 – Birger Jarl, Swedish regent and founder of Stockholm (b. c. 1210)
October 28 – Saint Arsenije I Sremac
October 29 – Margaret of Austria, Queen of Bohemia (b. c. 1204)
December – John of Ibelin, jurist of the Kingdom of Jerusalem (b. 1215)
December 3 – Henry III the White, Duke of Wroclaw
Berke, khan of the Golden Horde
Hugh Bigod, Justiciar of England
Ariq Böke, regent of the Mongol Empire
Maol Choluim II, Earl of Fife
Mo'ayyeduddin Urdi, astronomer and mathematician
Nasir ud din Mahmud, sultan of Delhi (b. 1246)
Year 1266 (MCCLXVI) was a common year starting on Friday (link will display the full calendar) of the Julian calendar.