|Ab urbe condita||2009|
|Balinese saka calendar||1177–1178|
|English Regnal year||40 Hen. 3 – 41 Hen. 3|
|Chinese calendar||乙卯年 (Wood Rabbit)|
3952 or 3892
— to —
丙辰年 (Fire Dragon)
3953 or 3893
|- Vikram Samvat||1312–1313|
|- Shaka Samvat||1177–1178|
|- Kali Yuga||4356–4357|
|Japanese calendar||Kenchō 8 / Kōgen 1|
|Minguo calendar||656 before ROC|
|Thai solar calendar||1798–1799|
1382 or 1001 or 229
— to —
1383 or 1002 or 230
|Wikimedia Commons has media related to 1256.|
- 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, founded by Danylo King of Rus, is first mentioned in the written account of Chełm fire.
- 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 in England.
- 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.
- The Church of Santa Costanza, Rome, is consecrated.
- The ancient Irish Kingdom of Breifne splits into East Breifne and West Breifne, after a war between the O'Reillys and the O'Rourkes.
- The War of the Euboeote Succession begins, involving most of the lords of Frankish Greece and the Republic of Venice.
- May – Mongol campaign against the Nizaris: Mongol forces capture and sack Tun (modern-day Ferdows), Persia and massacre its people.
- June 30 – A large volcanic eruption in Harrat Rahat (near Medina) is associated with an Islamic prophecy.
- September–October – The Japanese Kenchō era ends, and the Kōgen era begins.
- 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.
- November 19 – Nizari Ismaili Imam Rukn al-Din Khurshah surrenders to the invading Mongols under Hulagu while he is besieged in Maymun-Diz
- December 15 – Hulagu captures and dismantles the Alamut Castle after the surrender of the Nizari Ismaili leaders, disestablishing their state
- Hulagu Khan establishes the Ilkhanate dynasty of Persia, which will become one of four main divisions of the Mongol Empire.
- January 28 – William II, Count of Holland, King of Germany
- April 12 – Margaret of Bourbon, Queen of Navarre, regent of Navarre (b. c. 1217)
- June 13 – Tankei, Japanese sculptor (b. 1173)
- September 1 – Kujō Yoritsune, Japanese shōgun (b. 1218)
- September 21 – William of Kilkenny, Lord Chancellor of England
- October 14 – Kujō Yoritsugu, Japanese shōgun (b. 1239)
- Johannes de Sacrobosco, English scholar
- Þórður kakali Sighvatsson, Icelandic leader
- The Seismicity of Egypt, Arabia and the Red Sea: A Historical Review p. 40