May 22 – The Kings John (Lackland) and Philip II (Augustus) sign a peace treaty at Le Goulet, an island in the middle of the Seine River, near Vernon in Normandy. The agreement recognizes John as overlord of most of the English owned lands in France, but John has to give Philip the lands of Norman Vexin and Évreux and a large sum of money (some 20,000 marks) - a "relief" payment for recognition of John's sovereignty of Brittany.
Temüjin (or Genghis Khan) manages to unite about half the feuding Mongol clans under his leadership. He delegates authority based on skill and loyalty, rather than tribal affiliation or family. The main rivals of the Mongol confederation are the Naimans to the west, the Merkits to the north, the Tanguts to the south and the Jin Dynasty (or Great Jin) to the east.
The University of Paris receives its charter, from Philip II. He issues a diploma "for the security of the scholars of Paris", which affirms that students are subject only to ecclesiastical jurisdiction.
Spring – A treaty is signed between the Crusade leaders and Venice. Doge Enrico Dandolo agrees to manufacture a fleet capable of transporting the Crusader army to the Levant, and to provide provisions for 33,500 men and 4,500 horses, for the price of 85,000 silver marks while Venice will also take half of whatever the expedition conquers. As part of this deal the Venetians will provide - at their own expense - sufficient ships to carry the Crusader forces, plus 50 galleys to defend it.
King John (Lackland) puts an embargo on wheat exported to Flanders, in an attempt to force an allegiance between the states. He also puts a levy of a fifteenth on the value of cargo exported to France and disallows the export of wool to France without a special license. The levies are enforced in each port by at least six men - including one churchman and one knight. John affirms that judgments made by the court of Westminster are as valid as those made "before the king himself or his chief justice".
April–May – The bulk of the Crusader army gathers at Venice - although with far smaller numbers than expected: about 12,000 men (4-5,000 knights and 8,000 soldiers) instead of 33,500 men. Several contingents decide to make their own way to the Holy Land by different routes. A Crusader fleet sail from Flanders, carrying supplies for the Counts Baldwin IX and his brother Henry of Flanders, winters in Marseilles, but is slowed by adverse weather. Later it sails on to the Middle East, along with other contingents from southern France. 
Summer – The Crusader army, encamped on the island of San Niccolo di Lido between the Venetian Lagoon and the Adriatic Sea, is threatened by Doge Enrico Dandolo to keep them interned unless full payment is made as agreed (see 1201). As the Crusaders wait on the Lido for men to arrive, they also use up food supplies that Venice has agreed to supply. Dandolo faces a financial catastrophe, who has halted its commerce for a year's time, to prepare the expedition. The Crusader lords can offer Dandolo only 51,000 silver marks.
September 8 – Enrico Dandolo takes the cross and agrees to lead a Venetian force, which, in an outburst of Crusading enthusiasm, reaches some 21,000 men - the largest contingent of the Fourth Crusade. He proclaims the debts will be wiped, if the Crusaders take the 'rebel' Dalmatian city of Zadar, who has pledged its loyalty to Emeric, king of Hungary and Croatia. The Zadar proposal causes disquiet in the Crusader ranks - but it upset also Pope Innocent III threatening to excommunicate those who attack Zadar.
September – Prince Alexios Angelos sends representatives from Verona to the Crusader leaders in Venice, he promises to submit the Greek Orthodox Church to papal obedience and to provide the Crusade with 200,000 silver marks, together with provisions for a year. Alexios also will contribute 10,000 mounted soldiers to the expedition. In return he wants the Crusade to overthrow his uncle, the Byzantine emperor Alexios III (Angelos).
November 10–24 – Siege of Zadar: The Crusaders under Boniface of Montferrat besiege and conquer Zadar in Dalmatia. Despite letters from Innocent III forbidding such an action, and threatening excommunication. The leading citizens of Zadar hang banners of crosses along the outer walls, professing their Catholic faith. Nevertheless, the Crusaders breached and sacked the city, killing many.
Winter – Innocent III excommunicates the Crusader army, along with the Venetians, which winters at Zadar. Many Crusaders, including some senior men, either abandon the Fourth Crusade or make their own way to the Holy Land. However, the majority remains in Zadar, where the army receives some welcome reinforcements. During the winter, negotiations continue with Alexios Angelos.
Spring – King Philip II (Augustus) summons King John (Lackland) to Paris to answer his charges against the Lusignans. On April 28, failing to attend to Philip's court, John is declared to be a 'rebel' and to have forfeited the areas of Aquitaine, Poitou and Anjou. Philip tries to mediate the political problems between John and the Lusignans (who are charged with treason) but this is ignored by John. The lands are given to Arthur of Brittany. Philip supports Arthur's claim to the English throne and betrothed his 4-year-old daughter Marie.
July 27 – Battle of Basian: Seljuk forces (some 150,000 men) under Suleiman II of Rûm advance toward the Georgian border and are met by a 65,000-strong army led by King David Soslan, husband of Queen Tamar of Georgia at Basian. The Georgians assail the enemy's camp and in a pitched battle, the Seljuk forces are overwhelmed and defeated. The loss of the sultan's banner (while Suleiman himself is wounded), results in panic within the Seljuk ranks. The victory at Basian secures the Georgian preeminence in the region.
May–June – The Crusader fleet rounds Greece and stops at Negroponte (modern-day Halkis), where the local authorities submit to Alexios Angelos. Encouraged by this, the Crusader leaders sent him and several ships to extend his authority over the neighboring island of Andros. Mid-June, the Crusader fleet sails from Greece to Abydos, where it enters the Dardanelles.
June 23 – The Crusader fleet comes within sight of Constantinople and enters the Bosporus. The Byzantine capital is defended by a garrison of 15,000 soldiers (including 5,000 men of the Varangian Guard), and a fleet of 20 galleys. On June 26, the Byzantine troops skirmish with the Crusader forces who attack, without success, the cities of Chalcedon and Chrysopolis.
July 2 – Crusader leaders sail close to the city's walls in order to display the young Alexios Angelos, where they call upon the Byzantines to rise up in his favour. After rowing back and forth for a while, receiving insults and missiles, the attempt is abandoned. The Crusader leadership decided to land an invasion force north of Galata - using prevailing currents and winds.
July 5 – The Crusader fleet disembarks their horse transports and barreled down upon the Byzantine defenders in a full cavalry charge. The Byzantines flee after brief combat and retreat to the Tower of Galata, where they fortify themselves. After a bitter struggle, the Crusaders capture the tower and break the floating chain, and allow their fleet to enter the Golden Horn.
July 11 – The Crusaders take positions opposite the Palace of Blachernae on the northwest corner of the city. Their first attempts are repulsed, but on July 17 the Venetians take a section of the wall of about 25 towers, while the Varangian Guard holds off the Crusaders on the land wall, inflicting heavy casualties. The Venetians set fire to the buildings inside the Golden Horn walls, and then abandon the occupied fortifications.
July 17–18 – Alexios III tries to counterattack from the Gate of St. Romanus but retreats without a fight. Embarrassed, he preferred to escape and abandon his subjects, fleeing with the imperial treasure to Develtos (a fortified town on the Gulf of Burgas) in Thrace. Meanwhile, the Byzantine aristocracy restores the ex-emperor Isaac II to the imperial throne. On August 1, Alexios Angelos is crowned co-emperor as Alexios IV.
August – Alexios IV announces new taxes and enraged the Orthodox Church by confiscating large quantities of Byzantine icons, many centuries old, and melt them down to produce enough silver to pay the massive debt to the Venetians. A riot breaks out in Constantinople - during which the Byzantine populace loots and burns the homes of Italian residents in the city.
August 31 – The Venetians rally a rabble of soldiers and storm through the walls, attacking the Mitation Mosque which results in extensive fires in Constantinople. Finally, they are fought off by the Byzantines and Muslims standing side by side. It becomes one of the most extensive urban conflagrations in European History and renders some 100,000 people homeless.
August–October – Alexios IV leads a Crusader expedition (some 6,000 men) to extend his central-government control, against the fugitive Alexios III in Thrace. Meanwhile, a Crusader fleet operates in the Sea of Marmara in support of the Thracian campaign. The Crusaders seize several towns, including Adrianople, while Alexios escapes and withdraws to Macedonia.
William de Braose, an English nobleman, becomes the guardian at Rouen of the imprisoned 16-year-old Arthur of Brittany, designated heir to the throne of England - who is not known to be alive after April and is probably murdered by or at the orders of his uncle, John (Lackland).
August – Siege of Château Gaillard: French forces under Philip II begin the siege at Château Gaillard as part of a campaign to reconquer the continental properties of John (Lackland). During the winter of 1203/1204, the English under William Marshal attempt to relieve the castle.
Summer – On orders of Al-Adil I, sultan of Egypt, Muslim ships attack Crusader vessels off Cyprus. Ships from Acre retaliate this action, by capturing six Muslim ships off Acre. King Aimery of Jerusalem declares the truce void between Al-Aldil and the Crusaders, and raids Muslim territory in northern Palestine. Al-Adil responds by taking his army to the outskirts of Acre - but does not launch an assault and retires afterward. A plague breaks out in Acre and half the newly arrived Crusader army dies.
First evidence that the Temple in London is extending loans to John (Lackland). The sums remain small, but are often used for critical operations, such as the ransoming of the king's soldiers captured by the French.
March – Byzantine officials in Adrianople revolt and expel Latin administrators, requesting Bulgarian support from Kaloyan, ruler (tsar) of the Bulgarian Empire, against Baldwin I who assembles an army (some 40,000 men) and marches to aid the Byzantines. Meanwhile, Baldwin sets out from Constantinople in force, he arrives at Adrianople and promptly begins to siege the city by the end of March.
May 29 – Andrew II, brother of the late King Emeric, is crowned ruler of Hungary and Croatia at Székesfehérvár, after his 5-year-old nephew, Ladislaus III, suddenly dies in Vienna. Andrew introduces a new policy for royal grants, which he calls "new institutions". He distributes large portions of his domain-such as royal castles and all estates attached to them-to supporters and Hungarian nobles.
Summer – King Philip II (Augustus) conquers most of the Angevin lands, including much of Aquitaine. Fearing a French invasion of England itself, King John (Lackland) requires every English male over 12 years to enter a mobilization "for the general defense of the realm and the preservation of peace". John prepares an expedition force of his own, but the barons refuse to cross the Channel.
January 31 – Battle of Rusion: The Bulgarian forces (some 7,000 men) under Tsar Kaloyan defeat the remnants of the Latin army near the fortress of Rusion in Thrace. Around 120 knights supported by soldiers and cavalry are killed in battle or captured. In February, the Bulgarians attack and loot the fortified town of Rodosto (see Battle of Rodosto), defended by a Venetian garrison. Later, Kaloyan captures many more towns and fortresses.
Temüjin assembles at a Kurultai, a council of Mongol chiefs, the tribes under his rule and is elected as their leader. He is given the title of "Genghis Khan" of the Mongol people - founding the Mongol Empire. Genghis takes immediate steps to underpin his military command, starting with a fundamental reordering of tribal loyalties. United under one nomadic nation, under one banner and one authority.
Muqali (or Mukhali), a Mongol general in service of Genghis Khan, is rewarded with the command of the left-wing of the newly reorganized Mongol army and takes control over the eastern Mingghans.
King Valdemar II (the Conqueror) and Archbishop Andreas Sunonis raid Saaremaa Island (modern Estonia), forcing the islanders to submit. The Danes build a fortress, but finding no volunteers to man it, they burn it down themselves and leave the island.
June – King John (Lackland) lands an expeditionary army at La Rochelle to defend his interests in Aquitaine, which is his from the inheritance from his mother, Queen Eleanor of Aquitaine. Meanwhile, French forces led by King Philip II (Augustus) move south to meet John. The year's campaign ends in a stalemate and a two-year truce is made between the two rulers.
A peasant named Thurkhill in England claims that Saint Julian took him on a tour of Purgatory. Thurkhill includes realistic touches of descriptions of Purgatory's torture chambers. This is also believed by Roger of Wendover, one of his society's leading historians.
The Arab engineer Ismail al-Jazari describes many mechanical inventions in his book (title translated to English) The Book of Knowledge of Ingenious Mechanical Devices.
Spring – Siege of Attalia: Seljuk forces led by Sultan Kaykhusraw I besiege the city port of Attalia (modern-day Antalya) with siege machines. After a siege of more than 2 months, the city is captured, Kaykhusraw allows his forces 3-day looting and slaughtering. The capture of the port gives the Seljuk Turks a major path into the Mediterranean.
King John (Lackland) introduces the first income tax. One-thirteenth of income from rents, and moveable property has to be paid. Collected locally by sheriffs and administered by the Exchequer. The tax is unpopular with the English nobility and especially in the churches and monasteries. The tax does raise a lot of money for John, doubling his annual income for the year.
May 24 – John (Lackland) still refusing to accept Stephen Langton as archbishop, Innocent III threatens to place England under an Interdict. In response, John confiscates church property. Many of the English bishops of the great churches in the country flee abroad to the Continent.
November – Leeds, a market town in West Yorkshire, receives its first charter (approximate date).
April 15 – A fire breaks out in the Song Chinese capital city of Hangzhou, raging for four days and nights, destroying 58,097 houses over an area of more than 3 miles (4.8 km), killing 59 people, and an unrecorded number of other people, who are trampled while attempting to flee. The government provides temporary lodging for 5,345 people, in nearby Buddhist and Taoist monasteries. The collective victims of the disaster are given 160,000 strings of cash, along with 400 tons of rice. Some of the government officials who lost their homes take up residence in rented boathouses, on the nearby West Lake.
March 24 – Innocent III places England under an interdict, as punishment for King John (Lackland), for refusing to accept Stephen Langton as archbishop of Canterbury. During the interdict, religious services as marriages, burials, or baptisms cannot be performed. John confiscates church property of clergy who are unwilling to conduct services. Many bishops in the country flee abroad to the Continent.
November – John of England is excommunicated by Pope Innocent III. Despite the excommunication, John will continue to make amends to the Church, including giving alms to the poor whenever he defiles a holy day by hunting during it. This year, he feeds a hundred paupers to make up for when he "went into the woods on the feast of St. Mary Magdalen", and three years from now, he will feast 450 paupers "because the king went to take cranes, and he took nine, for each of which he feasted fifty paupers."
Black Monday, Dublin: A group of 500 recently arrived settlers from Bristol are massacred by warriors of the Gaelic O'Byrne clan. The group leaves the safety of the walled city of Dublin to celebrate Easter Monday near a wood at Ranelagh, and are attacked without warning. Although in modern times a relatively obscure event in history, it is commemorated by a mustering of the Mayor, Sheriffs and soldiers on the day, as a challenge to the native tribes for centuries afterwards.
Philippe Auguste of France grants a "conduit" to merchants going to the Champagne fairs, guaranteeing the safety of their travel, as any attempt made against them is now to be considered as a crime of lese-majesty. The decision increases again the appeal of the fairs, to merchants from Italy and the Low Countries.
^Steven Runciman (1952). A History of The Crusaders. Vol III: The Kingdom of Acre, pp. 93-94. ISBN978-0-241-29877-0.
^Warren, W. L. (1978). King John. University of California Press. p. 55.
^Warren, W. L. (1978). King John. University of California Press. p. 64.
^David Nicolle (2011). Osprey: Campaign - Nr. 237. The Fourth Crusade 1202-04. The betrayal of Byzantium, p. 17. ISBN978-1-84908-319-5.
^Andrew Roberts (2008). Great Commanders of the Medieval World (454-1582). Genghis Khan, p. 146. ISBN978-0-85738-589-5.
^Angold, Michael (2005). "Byzantine politics vis-à-vis the Fourth Crusade", in Laiou, Angeliki E. (ed.), Urbs capta: the Fourth Crusade and its consequences, Paris: Lethielleux, pp. 55-68. ISBN2-283-60464-8.
^Brand, Charles M. (1968). Byzantium confronts the West, 1180-1204, pp. 123-124. Cambridge, Massachusetts: Harvard University Press.
^David Nicolle (2011). Osprey: Campaign - Nr. 237. The Fourth Crusade 1202-04. The betrayal of Byzantium, p. 43. ISBN978-1-84908-319-5.
^David Nicolle (2011). Osprey: Campaign - Nr. 237. The Fourth Crusade 1202-04. The betrayal of Byzantium, p. 42. ISBN978-1-84908-319-5.
^Steven Runciman (1952). A History of The Crusades. Vol III: The Kingdom of Acre, p. 94. ISBN978-0-241-29877-0.
^Warren, W. L. (1961). King John. University of California Press. pp. 122-31.
^David Nicolle (2011). Osprey: Campaign - Nr. 237. The Fourth Crusade 1202-04. The betrayal of Byzantium, p. 19. ISBN978-1-84908-319-5.
^Ferris, Eleanor (1902). "The Financial Relations of the Knights Templars to the English Crown". American Historical Review. 8 (1).
^ abÞórðarson, Sturla (2012). "The Saga of Hacon, Hacon's Son". Icelandic Sagas and Other Historical Documents Relating to the Settlements and Descents of the Northmen of the British Isles. Volume 4: The Saga of Hacon, and a Fragment of the Saga of Magnus, with Appendices. Translated by George Webbe Dasent. Cambridge and New York: Cambridge University Press. p. 2. ISBN9781108052498. |volume= has extra text (help)
^Turner, Ralph V. (2009). King John: England's Evil King?, pp. 107-108. Stroud, UK: History Press. ISBN978-0-7524-4850-3.
^King John by Warren. Published by University of California Press in 1961. p. 139
^King John by Warren. Published by University of California Press in 1961. p. 11
^John V. A. Fine, Jr. (1994). The Late Medieval Balkans: A Critical Survey from the Late Twelfth Century to the Ottoman Conquest, pp. 87-91. Ann Arbor, Michigan: University of Michigan Press. ISBN0-472-08260-4.
^David Nicolle & Viacheslav Shpakovsky (2001). Osprey: Campaign Nr. 98: Kalka River 1223. Genghis Khan's Mongols invade Russia, p. 19. ISBN1-84176-233-4.