1250s

• The world population is estimated at between 400 and 416 million individuals.
• World climate transitions from the Medieval Warm Period to the Little Ice Age.[1]
• Medieval music: The Notre Dame school of polyphony ends.

• February – After the death of Erik Eriksson on February 2, Valdemar I, who is the eldest son of Birger jarl, is elected king of Sweden, and becomes the first Swedish king of the Folkung House.
• April 30 – King Louis IX of France is released by his Egyptian captors, after paying a ransom of one million dinars, and turning over the city of Damietta.
• October 12 – A great storm shifts the mouth of the River Rother 12 miles (20 km) to the west; a battering series of strong storms significantly alters other coastal geography as well (see Romney Marsh).
• December 13 – Frederick II, Holy Roman Emperor, dies, beginning a 23-year-long interregnum known as the Great Interregnum. Frederick II is the last Holy Roman Emperor of the Hohenstaufen Dynasty; after the interregnum, the empire passes to the Habsburgs.
• The Lombard League dissolves upon the death of its member states' nemesis, Frederick II, Holy Roman Emperor.
• King Afonso III of Portugal captures the Algarve from the Moors, thus completing the expulsion of the Moors from Portugal.
• Albertus Magnus isolates the element arsenic, as the 8th discovered metal. He also first uses the word oriole, to describe a type of bird (most likely the golden oriole).
• The University of Valladolid is founded in Spain.
• The Rialto Bridge in Venice (in present-day Italy) is converted from a pontoon bridge to a permanent, raised wooden structure.
• The Ponts Couverts fortified bridges of Strasbourg (in present-day France) are completed.
• Vincent of Beauvais completes his proto-encyclopedic work, The Greater Mirror.
• The first of the Parlements of Ancien Régime France is established.
• Villard de Honnecourt draws the first known image of a sawmill.
• The first usage is made of the English word 'cuckold,' according to the Oxford English Dictionary.

• A kurultai is called by Batu Khan in Siberia, as part of maneuverings to eventually elect Möngke Khan, as khan of the Mongol Empire in 1251.
• Starting in this year and ending in 1275, the Muslim Shougeng Pu serves as the Commissioner of Merchant Shipping for the Song Dynasty Chinese seaport at Quanzhou, due to his effort on defeating pirates, according to a monograph on the Chinese shipping industry and maritime economy, in dynasties of Tang and Sung written by Jitsuzo Kuwabara (桑原騭藏, 1870-1931). Shougeng Pu is likely a Persian or Arabic Muslim.

• April 6 – Battle of Fariskur: Louis IX of France is captured by Baibars' Mamluk army, while he is in Egypt conducting the Seventh Crusade; he later has to ransom himself.
• The Bahri Dynasty of Mamluks seize power in Egypt.
• The Welayta state is founded in present-day Ethiopia.
• In Tunis, a popular rebellion against newly arrived, wealthy and influential Andalusian refugees breaks out, and is violently put down.[2]

• Samoa frees itself from Tongan rule, which begins the Malietoa Dynasty in Samoa (approximate date)

• The Flemish town of Douai emits the first recorded redeemable annuities in medieval Europe, confirming a trend of consolidation of local public debt started in 1218, in Rheims.[3]
• The Sienese bankers belonging to the firm known as the Gran Tavola, under the steering of the Bonsignori Brothers, become the main financiers of the Papacy.[4]

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