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|Ab urbe condita||2019|
|Balinese saka calendar||1187–1188|
|English Regnal year||50 Hen. 3 – 51 Hen. 3|
|Chinese calendar||乙丑年 (Wood Ox)|
3962 or 3902
— to —
丙寅年 (Fire Tiger)
3963 or 3903
|- Vikram Samvat||1322–1323|
|- Shaka Samvat||1187–1188|
|- Kali Yuga||4366–4367|
|Japanese calendar||Bun'ei 3|
|Minguo calendar||646 before ROC|
|Thai solar calendar||1808–1809|
1392 or 1011 or 239
— to —
1393 or 1012 or 240
|Wikimedia Commons has media related to 1266.|
- 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.
- June 23 – War of Saint Sabas: In the Battle of Trapani, the Venetians defeat a larger Genoese fleet, capturing all its ships.
- 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 4000 merks.
- 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.
- January 11 – Swietopelk II, Duke of Pomerania
- February 12 – Amadeus of the Amidei, Italian saint
- 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, Syrian astronomer and mathematician
- Nasir ud din Mahmud, sultan of Delhi (b. 1246)
- "When Hebrideans were offered a new start in Norway". Scotsman. Retrieved 27 April 2018.
- "Manfred - king of Sicily". Encyclopedia Britannica. Retrieved 27 April 2018.
- "Malcolm (II), earl of Fife (d.1266)". db.poms.ac.uk. Retrieved 27 April 2018.