Pope Innocent III succeeded to the papacy in 1198, and the preaching of a new crusade became the goal of his pontificate. His call was largely ignored by the European monarchs: the Germans were struggling against Papal power, and England and France were still engaged in warfare against each other. However, due to the preaching of Fulk of Neuilly, a crusading army was finally organized at a tournament held at Écry by Count Thibaut of Champagne in 1199. Thibaut was elected leader, but he died in 1200 and was replaced by an Italian count, Boniface of Montferrat. Boniface and the other leaders sent envoys to Venice, Genoa, and other city-states to negotiate a contract for transport to Egypt, the object of their crusade; one of the envoys was the future historian Geoffrey of Villehardouin. Genoa was uninterested, but in March 1201 negotiations were opened with Venice, which agreed to transport 33,500 crusaders, a very ambitious number. This agreement required a full year of preparation on the part of the Venetians to build numerous ships and train the sailors who would man them, all the while curtailing the city's commercial activities. The crusading army was expected to comprise 4,500 knights (as well as 4,500 horses), 9,000 squires, and 20,000 foot-soldiers.
The majority of the crusading army that set out from Venice in October 1202 originated from areas within France. It included men from Blois, Champagne, Amiens, Saint-Pol, the Ile-de-France and Burgundy. Several other regions of Europe sent substantial contingents as well, such as Flanders and Montferrat. Other notable groups came from the Holy Roman Empire, including the men under Bishop Martin of Pairis and Bishop Conrad of Halberstadt, together in alliance with the Venetian soldiers and sailors led by the doge Enrico Dandolo. The crusade was to make directly for the centre of the Muslim world, Cairo, ready to sail on June 24, 1202. This agreement was ratified by Pope Innocent, with a solemn ban on attacks on Christian states.
As there was no binding agreement among the crusaders that all should sail from Venice, many chose to sail from other ports, particularly Flanders, Marseilles, and Genoa. By 1201 the bulk of the crusader army was collected at Venice, though with far fewer troops than expected; 12,000 instead of 33,500. Venice had performed her part of the agreement: there lay war galleys, large transports, and horse transports - enough for three times the assembled army. The Venetians, under their aged and blind Doge, would not let the crusaders leave without paying the full amount agreed to, originally 85,000 silver marks. The crusaders could only pay some 51,000 silver marks, and that only by reducing themselves to extreme poverty. This was disastrous to the Venetians, who had halted their commerce for a great length of time to prepare this expedition. In addition to this 20-30,000 men (out of Venice's population of 60,000 people) were needed to man the entire fleet, placing further strain on the Venetian economy.
Dandolo and the Venetians succeeded in turning the crusading movement to their own purposes as a form of repayment. Following the 1182 massacres of all foreigners in Constantinople, the Venetian merchant population had been expelled by the ruling Angelus dynasty with the support of the Greek population. These events gave the Venetians a hostile attitude towards Byzantium. Dandolo, who joined the crusade during a public ceremony in the church of San Marco di Venezia, proposed that the crusaders pay their debts by attacking the port of Zara in Dalmatia. The city had been dominated economically by Venice throughout the twelfth century, but had rebelled in 1181 and allied with King Emeric of Hungary and Croatia (the two were in a personal union). Subsequent Venetian attacks were repulsed, and by 1202 the city was economically independent, under the protection of the King.
The Hungarian king was Catholic and had himself agreed to join this Crusade (though this was mostly for political reasons, and he had made no actual preparations to leave). Many of the Crusaders were opposed to attacking Zara, and some, including a force led by the elder Simon de Montfort, refused to participate altogether and returned home. While the Papal legate to the Crusade Peter Cardinal Capuano endorsed the move as necessary to prevent the crusade's complete failure, Pope Innocent was alarmed at this development and wrote a letter to the Crusading leadership threatening excommunication.
Historian Geoffrey Hindley's The Crusades: Islam and Christianity in the Struggle for World Supremacy mentions that in 1202, Innocent III “forbade” the Crusaders of Western Christendom from committing any atrocious acts on their Christian neighbours, despite wanting to secure papal authority over Byzantium (Hindley 143, 152). This letter was concealed from the bulk of the army and the attack proceeded. The citizens of Zara made reference to the fact that they were fellow Catholics by hanging banners marked with crosses from their windows and the walls of the city, but nevertheless the city fell after a brief siege. Both the Venetians and the crusaders were immediately threatened with excommunication for this by Innocent III.
Boniface of Montferrat, meanwhile, had left the fleet before it sailed from Venice, to visit his cousin Philip of Swabia. The reasons for his visit are a matter of debate; he may have realized the Venetians' plans and left to avoid excommunication, or he may have wanted to meet with the Byzantine prince Alexius Angelus, Philip's brother-in-law and the son of the recently deposed Byzantine emperor Isaac II Angelus. Alexius had fled to Philip when his father was overthrown in 1195, but it is unknown whether or not Boniface knew he was at Philip's court. There, Alexius IV offered 200,000 silver marks, 10,000 men to help the Crusaders, the maintenance of 500 knights in the Holy Land, the service of the Byzantine navy to transport the Crusader Army to Egypt and the placement of the Greek Orthodox Church under the Roman Catholic Church if they would sail to Byzantium and topple the reigning emperor Alexius III Angelus. It was a tempting offer for an enterprise that was short on funds. Greco-Latin relationships had been complicated ever since the Great Schism of 1054.
The Latins of the First, Second, and Third Crusade had been hostile to Constantinople on their way to the Holy Land, whereas the Greeks had been accused of betraying the Crusaders to the Turks. A large number of Venetian merchants were also attacked and deported during anti-Latin riots in Constantinople in 1182. However, the Byzantine prince's proposal involved his restoration to the throne, not the sack of his capital city, which Count Boniface agreed to. Alexius IV returned with the Marquess to rejoin the fleet at Corfu after it had sailed from Zara. The rest of the Crusade's leaders eventually accepted the plan as well. There were many leaders, however, of the rank and file who wanted nothing to do with the proposal, and many deserted. The fleet of 60 war galleys, 100 horse transports, and 50 large transports (the entire fleet was manned by 10,000 Venetian oarsmen and marines) arrived at Constantinople in late June 1203. In addition, 300 siege engines were brought along on board the fleet.
When the Fourth Crusade arrived at Constantinople, the city had a population of 150,000 people, a garrison of 30,000 men (including 5,000 Varangians), and a fleet of 20 galleys. The Crusaders' initial motive was to restore Isaac II to the Byzantine throne so that they could receive the support that they were promised. Conon of Bethune delivered this message to the Lombard envoy who was sent by the reigning emperor Alexius III Angelus, who had deposed his brother Isaac. The citizens of Constantinople were not concerned with the deposed emperor and his exiled son; usurpations were frequent in Byzantine affairs, and this time the throne had even remained in the same family. The Crusaders sailed alongside Constantinople with 10 galleys to display Alexius III, but from the walls of the city the Byzantines taunted the puzzled crusaders, who had been promised that Prince Alexius would be welcomed. First the crusaders captured and sacked the cities of Chalcedon and Chrysopolis, then they defeated 500 Byzantine cavalrymen in battle with just 80 Frankish knights.
To take the city by force, the crusaders first needed to cross the Bosphorus. About 200 ships, horse transports and galleys would undertake to deliver the crusading army across the narrow strait, where Alexius III had lined up the Byzantine army in battle formation along the shore, north of the suburb of Galata. The Crusader's knights charged straight out of the horse transports, and the Byzantine army fled south.
The Crusaders followed south, and attacked the Tower of Galata, which held one end of the chain that blocked access to the Golden Horn. As they laid siege to the Tower, the Greeks counterattacked with some initial success. However, when the Crusaders rallied and the Greeks retreated to the Tower, the Crusaders were able to follow the soldiers through the Gate, and the Tower surrendered. The Golden Horn now lay open to the Crusaders, and the Venetian fleet entered.
On July 11, the Crusaders took positions opposite the Blachernae palace on the northwest corner of the city , and began the siege in earnest on July 17, with four divisions attacking the land walls, while the Venetian fleet attacked the sea walls from the Golden Horn. The Venetians took a section of the wall of about 25 towers, while the Varangian guard held off the Crusaders on the land wall. The Varangians shifted to meet the new threat, and the Venetians retreated under the screen of fire. The fire destroyed about 120 acres of the City.
Alexius III finally took offensive action, and led 17 divisions from the St. Romanus Gate, vastly outnumbering the crusaders. Alexius III's army of about 8,500 men faced the Crusader's 7 divisions (about 3,500 men), but his courage failed, and the Byzantine army returned to the city without a fight. The retreat and the effects of the fire greatly damaged morale, causing the citizens of Constantinople to turn against Alexius III, who then fled. The destructive fire left 20,000 people homeless. Prince Alexius was elevated to the throne as Alexius IV along with his blind father Isaac.
Thus Alexius IV had to deal with the growing hatred by the citizens of Constantinople for the "Latins" and vice versa. In fear of his life, the co-emperor asked the Crusaders to renew their contract for another six months, to end by April 1204. There was, nevertheless, still fighting in the city. In August 1203 the crusaders attacked a mosque, which was defended by a combined Muslim and Greek opposition. Meanwhile, Alexius IV had led 6,000 men from the Crusader army against his rival Alexius V in Adrianople.
On the second attempt of the Venetians to set up a wall of fire to aid their escape, they instigated the "Great Fire", in which a large part of Constantinople was burned down. Opposition to Alexius IV grew, and one of his courtiers, Alexius Ducas (nicknamed 'Murtzuphlos' because of his thick eyebrows), soon overthrew him and had him strangled to death. Alexius Ducas took the throne himself as Alexius V; Isaac died soon afterward, probably of natural causes.
The crusaders and Venetians, incensed at the murder of their supposed patron, demanded that Murtzuphlos honor the contract which Alexius IV had promised. When the Byzantine emperor refused the Crusaders assaulted the city once again. On April 8th, Alexius V's army put up a strong resistance which did much to discourage the crusaders.
The Greeks pushed enormous projectiles onto the enemy siege engines, shattering many of them. A serious hindrance to the crusaders was bad weather conditions. Wind blew from the shore and prevented most of the ships from drawing close enough to the walls to launch an assault. Only five of the Greek towers were actually engaged and none of these could be secured; by mid-afternoon it was evident that the attack had failed.
The clergy discussed the situation amongst themselves and settled upon the message they wished to spread through the demoralized army. They had to convince the men that the events of 9 April were not God's judgment on a sinful enterprise: the campaign, they argued, was righteous and with proper belief it would succeed. The concept of God testing the determination of the crusaders through temporary setbacks was a familiar means for the clergy to explain failure in the course of a campaign.
The clergy's message was designed to reassure and encourage the crusaders. Their argument that the attack on Constantinople was spiritual revolved around two themes. First, the Greeks were traitors and murderers since they had killed their rightful lord, Alexius IV. The churchmen used inflammatory language and claimed that "the Greeks were worse than the Jews", and they invoked the authority of God and the pope to take action.
Although Innocent III had again demanded that they not attack, the papal letter was suppressed by the clergy, and the crusaders prepared for their own attack, while the Venetians attacked from the sea; Alexius V's army stayed in the city to fight, along with the imperial bodyguard, the Varangians, but Alexius V himself fled during the night.
On 12 April 1204 the weather conditions finally favoured the Crusaders. A strong northern wind aided the Venetian ships to come close to the wall. After a short battle, approximately seventy crusaders managed to enter the city. Some Crusaders were eventually able to knock holes in the walls, small enough for a few knights at a time to crawl through; the Venetians were also successful at scaling the walls from the sea, though there was extremely bloody fighting with the Varangians. The crusaders captured the Blachernae section of the city in the northwest and used it as a base to attack the rest of the city, but while attempting to defend themselves with a wall of fire, they ended up burning down even more of the city. This second fire left 15,000 people homeless. The Crusaders took the city on April 12. The crusaders inflicted a horrible and savage sacking on Constantinople for three days, during which many ancient and medieval Roman and Greek works were either stolen or destroyed. The magnificent Library of Constantinople was destroyed. Despite their oaths and the threat of excommunication, the Crusaders ruthlessly and systematically violated the city's holy sanctuaries, destroying, defiling, or stealing all they could lay hands on; nothing was spared. It was said that the total amount looted from Constantinople was about 900,000 silver marks. The Venetians received 150,000 silver marks that was their due, while the Crusaders received 50,000 silver marks. A further 100,000 silver marks were divided evenly up between the Crusaders and Venetians. The remaining 500,000 silver marks were secretly kept back by many Crusader knights.
Speros Vryonis in Byzantium and Europe gives a vivid account of the sack of Constantinople by the Frankish and Venetian Crusaders of the Fourth Crusade:
The Latin soldiery subjected the greatest city in Europe to an indescribable sack. For three days they murdered, raped, looted and destroyed on a scale which even the ancient Vandals and Goths would have found unbelievable. Constantinople had become a veritable museum of ancient and Byzantine art, an emporium of such incredible wealth that the Latins were astounded at the riches they found. Though the Venetians had an appreciation for the art which they discovered (they were themselves semi-Byzantines) and saved much of it, the French and others destroyed indiscriminately, halting to refresh themselves with wine, violation of nuns, and murder of Orthodox clerics. The Crusaders vented their hatred for the Greeks most spectacularly in the desecration of the greatest Church in Christendom. They smashed the silver iconostasis, the icons and the holy books of Hagia Sophia, and seated upon the patriarchal throne a whore who sang coarse songs as they drank wine from the Church's holy vessels. The estrangement of East and West, which had proceeded over the centuries, culminated in the horrible massacre that accompanied the conquest of Constantinople. The Greeks were convinced that even the Turks, had they taken the city, would not have been as cruel as the Latin Christians. The defeat of Byzantium, already in a state of decline, accelerated political degeneration so that the Byzantines eventually became an easy prey to the Turks. The Crusading movement thus resulted, ultimately, in the victory of Islam, a result which was of course the exact opposite of its original intention.(Vryonis, Byzantium and Europe, p.152). According to Choniates, a prostitute was even set up on the Patriarchal throne. When Innocent III heard of the conduct of his pilgrims, he was filled with shame and strongly rebuked them.
According to a prearranged treaty, the empire was apportioned between Venice and the crusade's leaders, and the Latin Empire of Constantinople was established. Boniface was not elected as the new emperor, although the citizens seemed to consider him as such; the Venetians thought he had too many connections with the former empire because of his brother, Renier of Montferrat, who had been married to Maria Comnena, empress in the 1170s and 80s. Instead they placed Baldwin of Flanders on the throne. Boniface went on to found the Kingdom of Thessalonica, a vassal state of the new Latin Empire. The Venetians also founded the Duchy of the Archipelago in the Aegean Sea. Meanwhile, Byzantine refugees founded their own successor states, the most notable of these being the Empire of Nicaea under Theodore Lascaris (a relative of Alexius III), the Empire of Trebizond, and the Despotate of Epirus.
Almost none of the crusaders ever made it to the Holy Land, and the unstable Latin Empire siphoned off much of Europe's crusading energy. The legacy of the Fourth Crusade was the deep sense of betrayal the Latins had instilled in their Greek coreligionists. With the events of 1204, the schism between the Church in the West and East was complete. As an epilogue to the event, Pope Innocent III, the man who had launched the ill-fated expedition, thundered against the crusaders thus:
The Latin Empire was soon faced with a great number of enemies, which the crusaders had not taken into account. Besides the individual Byzantine Greek states in Epirus and Nicaea, the Empire received great pressure from the Seljuk Sultanate and the Bulgarian Empire. The Greek states were fighting for supremacy against both Latins and each other. Almost every Greek and Latin protagonist of the event was killed shortly after. Murtzuphlus' betrayal by Alexius III led to his capture by the Latins and his execution at Constantinople. Not long after, Alexius III was himself captured by Boniface and sent to exile in Southern Italy. One year after the conquest of the city, Emperor Baldwin was decisively defeated at the Battle of Adrianople on 14 April 1205 by the Bulgarians, and was captured and later executed by the Bulgarian Emperor Kaloyan. Two years after that, on 4 September1207, Boniface himself was killed in an ambush by the Bulgarians, and his head was sent to Kaloyan. He was succeeded by his infant son Demetrius of Montferrat, who ruled until he reached adulthood, but was eventually defeated by Theodore I Ducas, the despot of Epirus and a relative of Murtzuphlus, and thus the Kingdom of Thessalonica was restored to Byzantine rule in 1224.
Various Latin-French lordships throughout Greece — in particular, the duchy of Athens and the principality of the Morea — provided cultural contacts with western Europe and promoted the study of Greek. There was also a French cultural work, notably the production of a collection of laws, the Assises de Romanie (Assizes of Greece). The Chronicle of Morea appeared in both French and Greek (and later Italian and Aragonese) versions. Impressive remains of crusader castles and Gothic churches can still be seen in Greece. Nevertheless, the Latin Empire always rested on shaky foundations. The city was re-captured by the Nicaean Greeks under Michael VIII Palaeologus in 1261, and commerce with Venice was re-established.
In an ironic series of events, during the middle of the 15th century, the Latin Church tried to organize a crusade which aimed at the restoration of the Byzantine Empire which was gradually being torn down by the Ottoman Turks. The attempt, however, failed, as the vast majority of the Byzantines refused to unite the churches. The Greek population found that the Byzantine civilization which revolved around the Orthodox faith would be more secure under Ottoman rule. Overall, religious-observant Byzantines preferred to sacrifice their political freedom in order to preserve their faith's traditions and rituals. In the late 14th and early 15th century, two kinds of crusades were finally organised by the Kingdoms of Hungary, Poland, Wallachia and Serbia. Both of them were checked by the Ottoman Empire. During the Ottoman siege of Constantinople in 1453, a significant band of Venetian and Genoese knights died in the defense of the city.
In April 2004, in a speech on the 800th anniversary of the city's capture, Ecumenical Patriarch Bartholomew I formally accepted the apology. "The spirit of reconciliation is stronger than hatred," he said during a liturgy attended by Roman Catholic Archbishop Philippe Barbarin of Lyon, France. "We receive with gratitude and respect your cordial gesture for the tragic events of the Fourth Crusade. It is a fact that a crime was committed here in the city 800 years ago." Bartholomew said his acceptance came in the spirit of Pascha. "The spirit of reconciliation of the resurrection... incites us toward reconciliation of our churches."
The Fourth Crusade was one of the last of the major crusades to be launched by the Papacy, though it quickly fell out of Papal control. After bickering between laymen and the papal legate led to the collapse of the Fifth Crusade, later crusades were directed by individual monarchs, mostly against Egypt. Only one subsequent crusade, the Sixth, succeeded in restoring Jerusalem to Christian rule, and then only for a short time. The Crusades, as it seems, became politically and economically efficient for Crusaders less inclined to follow a spiritual but an ambitious, worldly conscience.