|Centuries:||12th century – 13th century – 14th century|
|Decades:||1220s 1230s 1240s – 1250s – 1260s 1270s 1280s|
|Years:||1256 1257 1258 – 1259 – 1260 1261 1262|
- 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 – The Empire of Nicaea defeats the Principality of Achaea at the Battle of Pelagonia, ensuring the eventual reconquest of Constantinople in 1261.
- December 4 – The 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 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 four year long civil war from 1260 to 1264. In the end, Ariq Böke surrendered to Kublai.
- While engaged in a war with the Mongols, the Song Chinese official Li Zengbo wrote in his Kozhai Zagao, Xugaohou that the city of Qingzhou was 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 (died 1330)
- Demetre II of Georgia (died 1289)
- John II of Jerusalem (died 1285)
- Richard Og de Burgh, 2nd Earl of Ulster (died 1326)
- Infanta Branca of Portugal, daughter of King Afonso III of Portugal and Urraca of Castile
- May 29 – King Christopher I of Denmark (born 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