Year 1256 (MCCLVI) was a leap year starting on Saturday (link will display the full calendar) of the Julian calendar.
May 4 – Pope Alexander IV issues the papal bull Licet ecclesiae catholicae, constituting the Order of Saint Augustine at Lecceto Monastery.
The city of Lviv, in present-day Ukraine, is founded by Danylo King of Rus.
Theodore II Lascaris, Byzantine Emperor (in exile in the Empire of Nicaea), successfully concludes a military campaign started a year earlier to recover Thrace from the Bulgarians.
Abingdon School is founded.
August 25: In Bologna slavery and serfdom is abolished, the event is recorded in the document called Liber Paradisus
Roger Bacon becomes a Franciscan Friar.
Church of Santa Costanza, Rome, is consecrated as a church.
The ancient Irish Kingdom of Breifne splits into East Breifne and West Breifne after a war between the O'Reillys and the O'Rourkes.
Beginning of the War of the Euboeote Succession, involving most of the lords of Frankish Greece and the Republic of Venice.
June 30 – A large volcanic eruption in Harrat Rahat near Medina is associated with an Islamic prophecy.
October – Mongol commander Baiju (operating under Hulagu Khan's command) leads his forces in a victory over Kay Ka'us II of the Sultanate of Rum, thereby capturing Anatolia.
December 15 – Hulagu Khan captures and destroys the Hashshashin stronghold at Alamut in present-day Iran.
Hulagu Khan establishes the Ilkhanate dynasty of Persia, which will become one of four main divisions of the Mongol Empire.
The Japanese Kenchō era ends, and the Kōgen era begins.
January 6 – Gertrude the Great, German mystic
Robert, Count of Clermont, French founder of the House of Bourbon (d. 1317)
Ibn al-Banna, Arabian mathematician (d. 1321)
January 28 – William II, Count of Holland, King of Germany
June 13 – Tankei, Japanese sculptor (b. 1173)
September 1 – Kujō Yoritsune, Japanese shogun (b. 1218)
September 21 – William of Kilkenny, Lord Chancellor of England
October 14 – Kujō Yoritsugu, Japanese shogun (b. 1239)
Johannes de Sacrobosco, English scholar
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