1257

1257 (MCCLVII) was a common year starting on Monday of the Julian calendar, the 1257th year of the Common Era (CE) and Anno Domini (AD) designations, the 257th year of the 2nd millennium, the 57th year of the 13th century, and the 8th year of the 1250s decade. As of the start of 1257, the Gregorian calendar was 7 days ahead of the Julian calendar, which was the dominant calendar of the time.

• Robert de Sorbon founds the Collège de Sorbonne at Paris, giving a formal college (and still-common name) to the already existing University of Paris in France.
• Matthew Paris, English historian, personally interviews King Henry III of England for a week straight while compiling his major work of English history, Chronica Majora.
• King Henry III of England orders the production of an twenty pence English coin of pure gold, the first high-denomination coin minted in England and the first to use gold. Unfortunately for King Henry, the bullion value of the coins was about 20% higher than the nominal face value, leading to poor circulation as coins were melted down by individuals for their gold content.
• The second Genoese War breaks out between Genoa and Venice in Outremer known as the War of Saint Sabas.
• The city of Kraków is rebuilt by Boleslaus V of Poland after being nearly destroyed in the Tatar invasions in 1241.
• The Japanese Kōgen era ends, and the Shōka era begins.
• Mongols take Annam (northern Vietnam).
• Aberdeen Grammar School opened.

• October 14 – King Przemysł II of Poland (d. 1296)
• Beatrice of Burgundy (died 1310)
• King Sancho IV of Castile and León (died 1295)

• June 4 – Duke Przemysł I of Greater Poland
• August 15 – Saint Hyacinth
• December 24 – John I, Count of Hainaut (born 1218)