* The Oxford Parliament, led by Simon de Montfort, 6th Earl of Leicester, leads to the acceptance by King Henry III of England of the Provisions of Oxford.
* September - Battle of Pelagonia: The Empire of Nicaea defeats the Principality of Achaea, ensuring the eventual reconquest of Constantinople in 1261.
* December 4 - Kings Louis IX of France and Henry III of England agree to the Treaty of Paris, in which Henry renounces his claims to French-controlled territory on continental Europe (including Normandy) in exchange for Louis withdrawing his support for English rebels.
* The famous frescoes of the Boyana Church in Bulgaria are completed (the church and its murals are now a UNESCO World Heritage Site).
* The German cities of Lübeck, Wismar, and Rostock enter into a pact to defend against pirates of the Baltic Sea, laying the groundwork for the Hanseatic League.
* Nogai Khan leads the second Mongol Golden Horde attack against Lithuania and Poland.


* August 11 - While conducting a siege against the Song Dynasty city known as Fishing Town in the province of Chongqing, China, the Mongol Khagan, Mongke Khan, dies in the nearby hills. Persian, Chinese, and Mongol records have different accounts of how he died, including succumbing to an arrow wound received by a Chinese archer in the siege, dysentery, and even a cholera epidemic. His death sparks a succession crisis in the Mongol Empire, while his brothers Ariq Böke and Kublai soon convene their own kuriltai to elect themselves as the next Khan of Khans, opening the path to a 4- year-long civil war from 1260 to 1264. In the end, Ariq Böke surrenders to Kublai.
* While engaged in a war with the Mongols, the Song Chinese official Li Zengbo writes in his "Kozhai Zagao, Xugaohou" that the city of Qingzhou is manufacturing one to two thousand strong iron-cased gunpowder bomb shells a month, dispatching to Xiangyang and Yingzhou about ten to twenty thousand such bombs at a time.
* Lannathai, a kingdom in the north of Thailand, is founded by King Mengrai.
* The Goryeo kingdom in Korea surrenders to invading Mongol forces.
* The Chinese era "Kaiqing" begins and ends in the Northern Song Dynasty of China.
* The Japanese Shōka era ends, and the Shōgen era begins.


* Pietro Cavallini, Italian painter (d. 1330)
* Demetre II of Georgia (d. 1289)
* John II of Jerusalem (d. 1285)
* Richard Og de Burgh, 2nd Earl of Ulster (d. 1326)
* Infanta Branca of Portugal, daughter of King Afonso III of Portugal and Urraca of Castile


* May 29 - King Christopher I of Denmark (b. 1219)
* October 7 - Ezzelino da Romano III, Italian ruler
* November 18 - Adam Marsh, English scholar and theologian
* Gojong of Goryeo
* Möngke Khan of the Mongol Empire
* Matthew Paris, English chronicler
* Thomas II of Savoy

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