The Fourth Crusade was a military campaign that was launched from Venice in 1202. It was originally raised to conquer Egypt, but the crusade was hijacked by the Venetians and resulted in the capture of Constantinople by the Crusaders and at the founding of the Eastern Latin Empire in 1204.
Call to Crusade
In 1198, only six years after the previous one, Pope Innocent III called for a new crusade; the appeal was ignored by the European lords. Indeed, after the failure of the previous crusade, Europe was reluctant to engage in another military campaign against the Muslims. The Germans were fighting against papal power and England and France were at war with each other.
Nevertheless, thanks to the preaching of Foulques de Neuilly, a Crusader army was finally organized at a tournament taking place in Écry by Count Thibaut III of Champagne in 1199. Thibaut was elected commander but died in 1200 and was replaced by an Italian count, Bonifacio of Montferrat. Boniface and the other leaders sent their emissaries, including the historian Geoffroi de Villehardouin, to Venice, Genoa and other city-states to negotiate a transport contract to Egypt. Indeed, the sovereigns of Europe had become convinced that the Byzantine Empire was hostile to their cause, so they now preferred to launch their crusade directly in Muslim lands, without going through Constantinople. Moreover, Egypt was one of the richest provinces in the East, and its conquest was to deal a fatal blow to the Muslims. Genoa declined the offer, but the Republic of Venice, which was the main maritime power in the Mediterranean, agreed to charter enough ships to transport 30,000 Crusaders, a considerable number.
Debt of the Crusaders to the Venetians
In 1201, the Crusader army met in Venice, although much smaller than expected. The Venetians were led by the old (and possibly blind) Doge of Venice, Enrico Dandolo; the latter refused that the ships leave the port without the Crusaders having paid the full amount, which was 85,000 silver ducats. The Crusaders were only able to pay 51,000, and even had to get there, being reduced to the most extreme poverty. The Venetians relegated the Crusaders to the Lido to decide what to do next.
Eventually, Dandolo agreed to defer the debt, in return for which the mighty army was to recapture the port of Zara (now Zadar in Croatia), a former Venetian possession in Dalmatia, for Venice. Dandolo made a big noise about his allegiance to the crusade during a ceremony held at Saint Mark's Basilica in Venice. This done, he led the Crusader fleet against the Hungarian port city. They arrived there on the night of November 11 and planned to spend the winter there, because Dandolo had not let them leave Venice in the summer[1]. But the Hungarian King Emeric was himself a Catholic and had also agreed to join the crusade. Many crusaders were opposed to this fratricidal attack and some returned home, including a division commanded by Simon IV de Montfort. The citizens of Zara hung banners bearing crosses from their windows to show that they were also Catholics; the Crusaders still besieged the city and took it. The Venetians and Crusaders were immediately excommunicated for this act by Pope Innocent III.
Diversion of the crusade to Constantinople
Boniface, who led the crusade, had however left the fleet before it left Venice and visited his cousin Philip of Swabia. The reasons for this visit are subject to debate:he may have understood the Venetian plans and tried to avoid excommunication. Perhaps he rather wanted to meet Alexis IV Ange, brother-in-law of Philippe and son of the Byzantine emperor Isaac II Ange, who had taken refuge with Philippe after the usurpation of the throne by his uncle Alexis III Ange. Isaac II had indeed been deposed in 1195 by his own brother and was kept prisoner in the jails of Constantinople, he had also been blinded.
Alexis made a proposal difficult to refuse to Boniface:the recovery of the throne of Byzantium against the payment of the debt of the crusaders in Venice. Perhaps Boniface also remembered the former possessions of his own brother, Conrad of Montferrat, who had married one of the daughters of the Byzantine emperor Manuel I Comnenus but had to leave the lands of the empire around 1190. Alexios and Boniface therefore joined together the Crusader fleet at Corfu, which the Crusaders had rallied after the capture of Zara. The Venetians were delighted with the idea of Alexis, because they had been offended by the behavior of the Byzantines towards them, especially because of the Constantinople riots of 1182 which cost the lives of many Europeans, many of whom were Venetians.
The crusaders were not inclined to fight against other Christians, but were convinced by the clergy that the orthodox Byzantines were almost as bad as the Muslims they had come to fight. Indeed, they had allied themselves with Saladin during the third crusade, and had done nothing to help the second crusade; they were to be punished for their lukewarmness. Alexis IV was persuaded to be welcomed as a liberator; unfortunately for him, the citizens of Constantinople preferred a usurper to an emperor supported by the “Latins”. The Crusaders and the Venetians decided to place him on the throne manu militari and an assault by sea took place in 1203. Strangely, Alexios III panicked before the opposing army and fled, leaving women and children in the city. The people of Constantinople had to reluctantly welcome Alexis IV, who was crowned emperor. His father, Isaac II was released from jail and installed co-emperor.
Civil war between Byzantines and Latins
The Crusaders were opposed to Isaac II's accession to the throne because they had never seen him, he was not part of the bargain, and he had previously allied himself with Saladin. However, the Byzantine citizens did not want Alexis as their sole ruler, as they had never seen him either. In this tense climate, Isaac II realized that the coffers of Byzantium had been emptied during his brother's reign, which forced Alexis IV to reconsider the terms of the deal he had offered to the Crusaders.
Alexis also had other worries:a real civil war was beginning to break out, because the citizens of Byzantium resented the presence of “Latins” in their city. Anti-Western opponents frequently attacked Crusaders they found in their path, and Alexios was forced to ask his allies to break camp and settle on the other side of the Golden Horn, the estuary that divides Constantinople in two. The clashes did not cease however, and during a cross attack on a mosque, which they were shocked to find in the Christian city, much of Constantinople was burned. A revolution against Alexis IV was then brewing and the leader of the anti-Western opposition, Alexis Doukas took power and had himself crowned Emperor Alexis V. Alexis IV was strangled and his father Isaac II also died in the following days, from death natural.
Second assault on the city
Crusaders and Venetians, enraged by the murder of their protector, attacked the city again in 1204. Alexios V, who had a much larger but less trained army, sent his troops outside the walls for an all-out assault on The crusaders. The latter were panicked and armed themselves with everything they could find, but the army of Alexis V turned around and returned to the city. It is possible that his infantry were afraid of the western knights who had already defeated them in skirmishes; however, the real cause of this decline is unknown. Against the advice of Pope Innocent III, the Crusaders attacked by land while the Venetians broke the heavy chain that blocked access to the Golden Horn, before launching a sea assault. The Varanges, who were the Imperial Guard, fought alongside the army of Alexis V, but Alexis himself fled after dark.
The crusaders dug holes in the walls, which allowed the knights to penetrate the enclosure; the Venetians also managed to destroy the ramparts by sea, but had to pay a heavy price in human lives at the Varanges. The Crusaders captured the northwestern part of the city around Blachernae Palace and used it as a base to assault the rest of the city. They defended themselves by creating a wall of fire, but the fire spread to cause an even more terrible conflagration than the first. The Crusaders were ultimately victorious, but considered by Byzantine citizens to be usurpers. The Westerners did not care and sacked the city for three days, during which many works of art were stolen or destroyed. The four horses that adorn Saint Mark's Basilica in Venice are one of the many testimonies to the sack of Constantinople.
Partition of the Byzantine Empire and weakening of the papacy
The Byzantine Empire was split between the Venetians and the Crusader lords according to a treaty concluded between the two parties; it was the birth of the Latin Empire of Constantinople. Boniface was not elected emperor, although the citizens considered him as such; the Venetians thought him too close to the old empire because of his brother's possessions and installed Frank Baudoin of Flanders on the throne. Boniface founded the Kingdom of Thessalonica, a vassal state of the new Latin Empire. The Venetians founded the Duchy of Naxos in the Aegean Sea, they constituted a vast colonial empire made up of counters located all along the sea route between Venice and Constantinople. The Byzantine refugees founded their own states, the largest of which was the Empire of Nicaea led by Theodore I Laskaris and the despotate of Epirus.
The Fourth Crusade had completely escaped the power of the papacy which had originated it. The latter subsequently lost much of its political power to European monarchs in general and the Holy Roman Emperor in particular. The Republic of Venice, on the other hand, strengthened considerably and made the most of this fourth crusade, at the expense of the Byzantine Empire. Subsequent crusades will be carried out by secular monarchs.