1251

Events 
 Europe 
 April – The first Shepherds' Crusade, a domestic French uprising in response to events in Egypt during the Seventh Crusade, occurs.
 December 26 – King Alexander III of Scotland marries Margaret, daughter of King Henry III of England, precipitating a power struggle between the two monarchs.
 Andrew de Longjumeau, dispatched two years earlier by King Louis IX of France as an ambassador to the Mongols, meets the king in Palestine, with reports from the Mongols and Tartary; his mission is considered a failure.
 Mindaugas of Lithuania is baptized, in prelude to his crowning as King of Lithuania in 1253.
 Alexander Nevsky signs the first peace treaty between Kievan Rus' and Norway.
 King Conrad IV of Germany invades Italy, but fails to subdue the supporters of Pope Innocent IV.
 The German city of Berlin, founded some fifty years earlier, receives its city charter.
 Ottokar II of Bohemia, later to become King of Bohemia, is elected Duke of Austria.
 The earliest known manuscript of The Proverbs of Alfred, a collection of sayings of England's Alfred the Great, is written.

 Asia 
 Möngke Khan is elected as the fourth great Khan of the Mongol Empire.
 Carving of the Tripitaka Koreana, a collection of Buddhist scriptures recorded on some 81,000 wooden blocks, is completed.

 Births 
 Hōjō Tokimune, 8th regent of the Kamakura shogunate (died 1284)

 Deaths 
 Bohemund V of Antioch
 Peter I, Duke of Brittany (born 1190)
 Eljigidei, Mongol commander of Persia
 Isobel of Huntingdon (born 1199)
 Matthias II, Duke of Lorraine