1252

Year 1252 (MCCLII) was a leap year starting on Monday (link will display the full calendar) of the Julian calendar.

Europe

 * April 6 – Saint Peter of Verona is assassinated by Carino of Balsamo.
 * May 15 – Pope Innocent IV issues the papal bull Ad exstirpanda, which authorizes the torture of heretics in the Medieval Inquisition. Torture quickly gains widespread usage across Catholic Europe.
 * June 1 – Alfonso X is proclaimed king of Castile and León.
 * July – The settlement of Stockholm in Sweden is founded, by Birger Jarl.
 * December 25 – Christopher I of Denmark is crowned King of Denmark, in the Lund Cathedral.
 * The Polish land of Lebus is incorporated into the German state of Brandenburg, marking the start of Brandenburg's expansion into previously Polish areas (Neumark).
 * The Lithuanian city of Klaipėda (Memel) is founded by the Teutonic Knights.
 * The town and monastery of Orval Abbey in Belgium burn to the ground; rebuilding takes 100 years.
 * Thomas Aquinas travels to the University of Paris, to begin his studies there for a master's degree.
 * In astronomy, work begins on the recording of the Alfonsine tables.

Asia

 * The classic Japanese text Jikkunsho is completed.
 * The Chinese era Chunyou ends.
 * The Mongols take the westernmost province of the Song dynasty empire.

Births

 * March 25 – Conradin, Duke of Swabia (d. 1268)
 * Safi-ad-din Ardabili, Persian Sufi leader
 * Eleanor de Montfort, Princess of Wales, English-born consort (d. 1282)

Deaths

 * January 1 – Saint Zdislava Berka, Bohemian lay Dominican benefactress
 * January 23 – Isabella, Queen of Armenia
 * January – Bohemond V, Prince of Antioch
 * February 3 – Sviatoslav III of Vladimir, Prince of Novgorod (b. 1196)
 * April 1 – Kujō Michiie, Japanese regent
 * April 6 – Saint Peter of Verona
 * May 3 or May 4 – Günther von Wüllersleben, Grand Master of the Teutonic Knights
 * May 30 – King Ferdinand III of Castile and Leon
 * June 6 – Robert Passelewe, Bishop of Chichester
 * June 9 – Otto I, Duke of Brunswick-Lüneburg
 * June 29 – Abel, King of Denmark (b. 1218)
 * August 1 – Giovanni da Pian del Carpine, Italian chronicler of the Mongol Empire
 * November 27 – Blanche of Castile, queen of Louis VIII of France and regent of France (b. 1188)
 * date unknown
 * John of Basingstoke, English scholar and ecclesiastic
 * Henry I, Count of Anhalt
 * Sorghaghtani Beki, Mongolian empress and regent
 * Catherine Sunesdotter, Swedish queen consort
 * Yesü Möngke, Khan of the Chagatai Khanate