Year 1204 (MCCIV) was a leap year starting on Thursday of the Julian calendar.
Events
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- January 27–28 – Byzantine emperor Alexios IV Angelos is overthrown in a revolution.
- February – A large solar storm takes place, and is recorded in the diary of the Japanese poet Fujiwara no Teika.
- February 5 – Alexios V Doukas is crowned Byzantine emperor.thumb|right|150px|Conquest of Constantinople by the Crusaders
- April 12 – Sack of Constantinople: Crusaders enter Constantinople by storm and start pillaging the city as part of the Fourth Crusade.
- May 16 – Baldwin, Count of Flanders, is crowned emperor of the Latin Empire a week after his election by the members of the Fourth Crusade.
- Theodore I Laskaris flees to Nicaea after the capture of Constantinople, and establishes the Empire of Nicaea; Byzantine successor states are also established in Epirus and Trebizond.
- Boniface I, Marquis of Montferrat, a leader of the Fourth Crusade, founds the Kingdom of Thessalonica.
- The writings of French theologian Amalric of Bena are condemned by the University of Paris and Pope Innocent III.
- Tsar Kaloyan is recognized as king of Bulgaria by Pope Innocent III, after the creation of the Bulgarian Uniate church.
- Valdemar II of Denmark is recognized as king in Norway.
- Angers and Normandy are captured by Philip II of France.
- The Cistercian convent of Port-Royal-des-Champs is established.
- The district of Cham becomes subject to Bavaria.
- Hermann I, Landgrave of Thuringia submits to Philip of Swabia.
- Beaulieu Abbey is founded.
- The Channel Islands of Guernsey and Jersey decide, after a plebiscite of wealthy land owners, to remain with the English crown, after Normandy is recaptured by Philip II of France.</onlyinclude>
- Landshut, Bavaria, is Founded.
Births
- April 14 – Henry I, king of Castile (d. 1217)
- Haakon IV of Norway (d. 1263)
- Henry Raspe, Landgrave of Thuringia (d. 1247)
- Maria of Courtenay, Empress regent of Nicaea (d. 1228)
- Alice of Schaerbeek (d. 1250)
Deaths
- January 1 – King Haakon III of Norway
- February 8 – Alexios IV Angelos, Byzantine emperor
- April 1 – Eleanor of Aquitaine, Sovereign Duchess Regnant of Aquitaine, queen of France and England
- August 11 – King Guttorm of Norway
- August 14 – Minamoto no Yoriie, Japanese shōgun (b. 1182)
- September 30 or November 30 – Emeric, King of Hungary (b. 1174)
- c. October 21 – Robert de Beaumont, 4th Earl of Leicester, English nobleman
- November – Ban Kulin, ruler of Bosnia (b. 1163)
- December 12 (or December 13) – Maimonides, Spanish rabbi and philosopher (b. 1135)
- December 22 – Fujiwara no Shunzei, Japanese waka poet (b. 1114)
- date unknown – Suleiman II, Sultan of Rûm
- probable – Amalric of Bena, French theologian