|Covid-19|Observed effects of an eruption of the Indonesian volcano Mount Rinjani in late 1257 include the following anecdotal accounts: dry fog in France; lunar eclipses in England; severe winter in Europe; a "harsh" spring in northern Iceland; famine in England, western Germany, France, and northern Italy; and pestilence in London, parts of France, Austria, Iraq, Syria, and south-east Turkey.
February 10 – The Siege of Baghdad ends with a battle in which Hulagu Khan's Mongol forces overrun Baghdad, then the leading center of Islamic culture and learning and capital of the Abbasid Caliphate. They burned the imperial city to the ground, killing as many as 1,000,000 citizens, and destroyed the House of Wisdom containing countless precious historical documents and books on subjects ranging from medicine to astronomy.
The Chinese era Baoyou ends in the Northern Song dynasty of China.
Korea surrenders to the Mongols, ending the effective resistance of the Choe faction within Korea.
The Mongol Empire invades the Đại Việt (present-day northern Vietnam).
May 11 – Treaty of Corbeil between James I of Aragon and Louis IX of France. The French king, as the heir of Charlemagne, formally renounced its feudal overlordship over Catalonia (independent de facto since 988) while the Aragonese king renounced its claims over Occitania.
August 25 – George Mouzalon, regent of the Empire of Nicaea, is assassinated in Magnesia ad Sipylum as part of a conspiracy led by nobles under future emperor Michael VIII Palaiologos.
Llywelyn ap Gruffudd declares himself Prince of Wales. He is the final ruler of an independent Wales, before its conquest by the English.
King Henry III of England is forced by seven powerful barons to accept the Provisions of Oxford.
Gissur Þorvaldsson is made Earl of Iceland by King Haakon IV of Norway.
Mongol Golden Horde attack against Lithuania.
The Battle of Karydi ends the War of the Euboeote Succession in a crushing victory for William II of Villehardouin, Prince of Achaea.
In Genoa, the Republic starts imposing forced loans, known as luoghi to its taxpayers; they are a common resource of medieval public finance.
Civil unrest in northern Italy spawns the medieval musical form of Geisslerlieder, penitential songs sung by wandering bands of Flagellants.
The Mongols murdered the Abbasid Caliph and ended the long standing Islamic Empire
Osman I, founder of the Ottoman Empire (d. 1326)
Trần Nhân Tông, emperor of Vietnam (d. 1308)
Arghun, fourth Ilkhanate ruler of Iran (d. 1291)
Henryk IV Probus, Duke of Wrocław (d. 1290)
February – Sulaiman Shah, Abbasid soldier
February 20 – Al-Musta'sim, last Abbasid Caliph of Baghdad
April 5 – Saint Juliana of Liège
June 2 – Peter I, Count of Urgell
July 22 – Meinhard I, Count of Gorizia-Tyrol (b. c. 1200) (alternative date is February)
August 18 – Theodore II Laskaris, emperor of Nicea (Byzantine emperor in exile)
August 25 – George Mouzalon, regent of the Empire of Nicaea
November 10 – William de Bondington, Bishop of Glasgow
Abul Hasan ash-Shadhili, Moroccan spiritual leader (b. 1175)
Clement of Dunblane, first Dominican bishop in Britain
Hong Bok-won, Goryeo commander who later served the Mongol Empire
Ingerd Jakobsdatter, Danish countess (b. 1200)
Year 1258 (MCCLVIII) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar.