Europe

• Spring – Prince Alexander Nevsky is joined by his brother Andrey II (Yaroslavich) at Novgorod, supported with his elite druzhina (or 'household') from Suzdal. They head southwest across the frozen marshes, which cover much of the land between Novgorod and Pskov. On March 5, Alexander retakes the city almost without a struggle, before the larger Crusader garrison in nearby Izborsk can intervene.^[1]
• April – A Russian force led by Alexander Nevsky crosses the frontier between Novgorod and Livonian Crusader territory, to raid into Catholic Estonia. After that, Alexander breaks his army off into contingents to ravage the countryside. He is forced to turn back, when a local Crusader force under Bishop Hermann von Buxhövden defeats Alexander's advance guard at Mooste bridge south of Tartu.^[2]
• April 5 – Battle of Lake Peipus (or Battle on the Ice): Russian forces led by Alexander Nevsky, rebuff an invasion attempt by a Crusader army (some 2,600 men), including German Teutonic Knights. The opposing armies meet upon the frozen surface of Lake Peipus. The outnumbered Teutonic Knights are defeated on the slippery surface, by Alexander's elite druzhina and the Novgorod forces.^[3]
• May 28 – Avignonet massacre: A group of Cathars, with the probable connivance of Count Raymond VII of Toulouse, murder the inquisitor William Arnaud and eleven of his companions.^[4]
• July 21–22 – Battle of Taillebourg: French forces (some 25,000 men) under King Louis IX (the Saint) defeat King Henry III at the bridge over the Charente River near Taillebourg. After the battle, Louis continues to pursue the English troops, capturing many prisoners. Henry retreats with the remnants of his army to Bordeaux, where he spends the winter.
• Summer – Alexander Nevsky sends envoys to Batu Khan, preemptively capitulating before the Mongols even though they have not reached Novgorod, and accepts his rule as Mongol overlord.
• November 16 – King Béla IV issues the Golden Bull to the inhabitants of Gradec (modern-day Zagreb) and Samobor in Croatia. By this golden bull, Béla proclaimes Gradec a royal free city.
• Siegfried III, archbishop of Mainz, conquers Wiesbaden (a free imperial city) and orders the city's destruction, during the war of Emperor Frederick II against the Papal States.
• King Sancho II (the Pious) conquers the cities of Tavira, Alvor and Paderne, in his continuing expansion against the Muslims, known as the Reconquista.^[5]

Mongol Empire

• Spring – Siege of Esztergom: The Mongols under Batu Khan assault and destroy most of the Hungarian city of Esztergom. Batu Khan sends a reconnaissance party against the Holy Roman Empire.
• Battle of Grobnik Field: Croatian forces under Béla IV stop the Mongol invasion in Hungary and Croatia. Béla rebuilds the country and orders the building of fortifications through his kingdom.
• Siege of Sernya: Mongol forces led by Subutai besiege and capture Sernya. During the siege, Queen Narchat is killed as she and a small group of warriors attempt to flee the city.^[6]
• Batu Khan establishes the Golden Horde at Sarai and withdraws his forces after messengers arrive with the news that the Great Khan Ögedei Khan has died (see 1241).

England

• May – Isabella of Angoulême, mother of Henry III, persuades him to mount an expedition to retake Poitou. On May 20, Henry arrives at Royan and joins the rebelling French nobles – forming an army (some 30,000 men). Louis IX exchanges letters with Henry to resolve the conflict, but the dispute escalates further.

Africa

• Summer – In the Maghreb, after a string of successes against the Almohad Caliphate, Hafsid forces under Sultan Abu Zakariya Yahya, conquer the city of Tlemcen (modern Algeria). The Kingdom of Tlemcen becomes a vassal of Abu Zakariya, and is formed in a series of small states between his rule and the states of the Western Maghreb.^[7]

Middle East

• Spring – The Templar Knights raid the city of Hebron. Meanwhile, An-Nasir Dawud, Ayyubid ruler of Damascus, sends forces to cut off the road to Jerusalem, and to levy tolls on the pilgrims and merchants that pass by.^[8]

• Death of Abbasid caliph al-Mustansir and succession of al-Musta'sim to the Caliphal throne.

Asia

• February 10 – The 10-year-old Emperor Shijō (or Mitsuhito) dies suddenly, despite a dispute over who should follow him as sovereign, Go-Saga (son of former Emperor Tsuchimikado) ascends to the throne of Japan.

Religion

• William of Modena, Italian bishop and papal diplomat, sets up four dioceses in Poland, including the Archdiocese of Warmia.

Science

• Ibn al-Nafis, Arab polymath and writer, suggests that the right and left ventricles of the heart are separate, and describes the lesser circulation of blood.