The Fourth Crusade lasted from 1201-1204. Though the Crusades were for the most part an entirely Western phenomenon, this one affected Eastern Church history because the invading Crusaders took Constantinople on April 13, 1204. After defeating the Byzantine Emperor Alexius V (who had usurped the throne from his predecessor Alexius IV, put in power by the Crusaders), they conquered the city and famously looted and desecrated numerous churches, icons, and relics.1 They then set up the Latin Empire, based in Constantinople; it lasted over 57 years until the Byzantine Michael VIII Palaeologus recaptured Constantinople in 1261. This Crusade is widely regarded as having finalized the Great Schism, as much bitterness towards the West remained even after the restoration of Byzantium.
- 1 Background
- 1.1 Papal primacy as developed during the Cluniac Reformation (10th-11th c.) and the Gregorian Reform of Pope Gregory VII.
- 1.2 Resentment against Eastern Christendom
- 1.3 Anti-Byzantine Sentement in connection with Previous Crusades and Byzantine Relations with Muslim Empires
- 1.4 Commercial Rivalries with Constantinople and Subsequent Avarice
- 1.5 Chronology of Aggressive Actions Between the West and Byzantium
- 2 Diversion to Constantinople
- 3 Papal Apology to Orthodox Church
- 4 Further reading
- 5 Sources
After the failure of the Third Crusade (1189–1192), there was little interest in Europe for another crusade against the Muslims. Jerusalem was now controlled by the Ayyubid dynasty, which ruled all of Syria and Egypt, except for the few cities along the coast still controlled by the crusader Kingdom of Jerusalem, now centered on Acre. The Third Crusade had also established a kingdom on Cyprus.
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 Bishops Martin of Pairisand and Conrad of Halberstadt, together in alliance with the Venetian soldiers and sailors led by the Doge of Venice 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.
Papal primacy as developed during the Cluniac Reformation (10th-11th c.) and the Gregorian Reform of Pope Gregory VII.
The Monastery of Cluny in French Burgundy taught the high doctrine of the power of the Apostolic See. The Church was to be organized under strict discipline, and bishops, priests, and monks had no rights of their own that were not derived from the pope, the unique source of ecclesiastical authority. In 1039 Cluny's abbot Odilo turned his monastery into the head of a monastic feudal system whose influence spread all over Europe. In 1055 the Monastery of Cluny captured the papacy. Pope Innocent III (pope during the Fourth Crusade) carried these Cluniac ideas about the position of the pope as the sole and highest authority in the Church.
It naturally followed, therefore, that Pope Gregory VII (1073-85) conceived of his supremacy over the temporal powers as a domination over both the Eastern and Western Empires. This Gregorian Reform stressed, among other things, the primacy of the papacy over the Empire, the infallability of the Church, and the right of popes to depose emperors.
With this background, and with the experience of the Great Schism in 1054, the papacy's position was that Byzantium was regarded as a rebel, a schismatic or heretical nation which should be brought back to order or eliminated.
Resentment against Eastern Christendom
The average European, especially those who lived in the northern territories and had no communication or knowledge of the Byzantine Empire, were taught to believe that the Greeks were ungodly, a nation not worthy to bear the name of Christians. One example is found in the Chronicle of the Morea (a 14th Century text naarating the establishment of western-style feudalism in Frankish Greece), there is a speech recorded which clearly shows the division between the Latins and the Greeks; the papal legate at Zara (1202) stated: "It is better to brings Christians into agreement and like-mindedness, the Franks and the Greeks, than go to Syria with no hope of success."(Chronicle of Morea p.82).
Also, in the acccount of the Second Crusade (1147-49), De profectione Ludovici VII in Orientem (On Louis VII's journey to the East), written by Odo of Deuil, a chaplain to the French King Louis VII and later abbott of Saint-Denis, Odo explains the failure of the Crusade in terms of human action rather than as the will of God. He blamed the Byzantine Empire under Manuel Comnenus for the downfall of the Crusade. Odo's prejudice against Byzantium led historian Steven Runciman to describe Odo as "hysterically anti-Greek."
Anti-Byzantine Sentement in connection with Previous Crusades and Byzantine Relations with Muslim Empires
Emperor Alexius I Comnenus helped the First Crusade but was very cautious, signing an uneasy treaty and alliance with the Crusaders. Emperor Manuel I Comnenus promised to help the Second Crusade and signed the same treaty with the Crusaders. However, he could not help because he was engaged in war against the Norman Prince Roger of Sicily, who had invaded Corfu. Manuel had also signed a treaty with the Turks of Iconium; the Crusaders, particularly the Franks, bitterly blamed him for their failure. Emperor Isaac II Angelus foolishly imprisoned the ambassadors of Emperor Frederick I Barbarossa (Hohenstauffen), head of the Third Crusade, who were sent to negotiate passage through imperial territory. Issac also had concluded a treaty with the Sultan of Iconium, as he was fearful of Frederick's ambitions.
Constantinople was always suspicious of the "Western hordes", sometimes quite unruly, which were passing through its territory full of bigotry and fanaticism against the Islamic nations neighboring the Empire. Besides, the policy of the Byzantine Empire in handling the Moslems and keeping them away was quite opposite to the Crusaders' ideals and blind religious fanaticism. Historian Queller, quoting Runciman, says that "the concept of Christian War appears to be alien to the thought and personality of Jesus, and in fact, it was not looked upon favorably by the Greek Church."
Commercial Rivalries with Constantinople and Subsequent Avarice
Envy for the apparent wealth of the Greeks and perhaps the desire to share in some of the precious holy relics and treasure in the churches of the imperial capital was another motivation. The primary sources of the First Crusade speak of the awe the Crusaders felt when they first glanced at the Imperial City and the domes of Hagia Sophia; the feeling of inferiority is openly discerned as being at work in the Crusaders as a result.
More to the point, in both of the accounts of Villehardouin and that of the Crusader knight Robert of Clari (4th Crusade), the impression of the Crusaders is recorded. They were stunned by the unbelievable wealth and the treasure of the holy relics of Constantinople.
Chronology of Aggressive Actions Between the West and Byzantium
- There were bitter memories of recent Byzantine attacks on Westerners (in Sicily, West Greece in 1098, and in Antioch during the First Crusade).
- 1149: The King of France Louis VII supported the suggestion that a European League should launch a new crusade against the emperor who was "Christian Only in Name." The capture of Constantinople should be the crusaders first objective. The Norman Roger of Sicily was in support of the idea, but his ally Pope Eugenius III was hesitant only because he feared the possible increase of Roger's power.
- 1171: Emperor Manuel, having concluded alliances with Pisa and Genoa, decided to strike at Venice by arresting all Venetians in the Empire and confiscating all their ships and goods, symbolizing the degeneration of the Empire's relationship with the West and between Latins and Greeks in Constantinople.
- 1183-85: During the reign of Emperor Andronicus I Comnenus, there was a great massacre of Italians in Constantinople, and all commerical concessions were withdrawn. Andronicus made many enemies and was eventually overthrown by riots in Constantinople.
- 1185: Normans took Thessaloniki and subjected inhabitants to merciless treatment, partly for revenge of the massacre of Latins in 1183.
- 1188: Emperor Isaac II agreed in 1188 to Sultan Saladin's request to build a new mosque (and not just use an existing one) in Constantinople. Its construction is mentioned by Pope Innocent III in a letter of 1210 to the Latin Patriarch of Constantinople, Tommaso Morosini. (Patrologia Latina, CCXVI, col. 354.)
- 1189: The Third Crusade (1189), headed by German King Frederick Barbarossa, an enemy of Byzantium, was almost turned against Constantinople. The folly of Isaac I in imprisoning Frederick's ambassadors enraged the Crusaders. They occupied Philippopolis in Thrace, and Frederick wrote to his son Henry to send a fleet and attack the capital. He also wrote to the pope for his blessing, stating that it was necessary to eliminate the Empire if they were going to have any success in their enterprise against the Moslems. Negotiations by Isaac and a treaty averted the danger at that time.
- 1191: Cyprus taken from Byzantines by English King Richard I "Lion Heart," who sold it in 1198 to Frankish Crusaders from previous Crusades ousted from Jerusalem in 1187 when the Arabs retook Jerusalem after 88 years.
- 1197: Henry VI, son of Frederick Barbarossa, made no secret of his hatred of Byzantium and his ambitions to build a Mediterranean dominion. In 1197 a German expedition landed at Acre in Palestine; it was to be the forerunner of a greater army led by Henry himself. Pope Celestine III made no attempt to dissuade him, but he advised him not to attack Constantinople because he was negotiating with the emperor the Union of the Churches. Henry's sudden death at 32 put an end to this German expedition.
Diversion to Constantinople
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.
Siege of July 1203
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.
Further attacks on Constantinople
Alexius IV realised that his promises were hard to keep. Alexius III had managed to flee with 1,000 pounds of gold and some priceless jewels, leaving the imperial treasury short on funds. At that point the young emperor ordered the destruction and melting of valuable Byzantine and Roman icons in order to extract their gold and silver, but even then he could only raise 100,000 silver marks. In the eyes of all Greeks who knew of this decision, it was a shocking sign of desperation and weak leadership, which deserved to be punished by God. The Byzantine historian Nicetas Choniates characterized it as "the turning point towards the decline of the Roman state".
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 8, 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 April 9 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.
Final capture of Constantinople
On April 12 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:
(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.
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.
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.
Sir Edward Gibbon stated that the spoils taken during one week in Constantinople equalled seven times the whole revenue of England at that time (Treece). The four magnificent bronze horses over the portals of San Marco's Basilica in Venice were snatched from the Byzantine hippodrome, standing monuments of one of the greatest acts of brigandage in history.
Its hard to exaggerate the harm done to European civilization by the sack of Constantinople. The treasures of the city, the books and works of art preserved from distant centuries, were all dispersed and most destroyed. The Empire, the great Eastern bulwark of Christendom, was broken as a power. The conquests of the Ottomans were made possible by the Crusaders' crime (Runciman, p.46).
A Roman Catholic patriarch was established and attempted to introduce Roman Catholicism by force. The new Venetian Patriarch in Constantinople, Tommaso Morosini, was appointed by the Doge of Venice, Enrico Dandolo (the main person who engineered the diversion of the Fourth Crusade); and according to Gibbon, the Venetians employed every art to perpetuate in their own nation the honors and benefices of the Greek church. Morosini appealed to the Pope for aid, and being unable to serve so many derisive masters, he died a madman. The new papal legate, Pelagius, rode into Constantinople dressed in scarlet from head to foot, like a Greek Emperor himself, and soon asserted that the easy days were over: Thenceforth the Greek clergy must adapt themselves in all religious rites and beliefs to those of the Church of Rome. He was prepared to wade through blood, he quickly showed, should the Orthodox Greeks deny any part of his assertion (Treece, pp.230-231).
After the Battle of the Olive Grove of Koundouros, which took place in the spring of 1205, in Messinia, Peloponnese, between the Franks and the Greeks, all the castles and cities of the Peloponnese fell to the Franks. Meanwhile, the Venetians took possession of Crete in 1211, and retained it until ousted by the Ottoman Turks in 1669, a full 458 years later.
In 1261 Emperor Michael Palaeologus reconquered Constantinople for the Byzantines, and control of the city at last passed from the Venetians to the Paleologus Dynasty. Emperor Michael VIII Palaeologus made the city of Mystras in the Peloponnese the seat of the new Despotate of Morea, which was to last until 1460.
Papal Apology to Orthodox Church
In May of 2001, Pope John Paul II visited Athens, Greece, the first visit of a pope in nearly 1300 years. Pope John Paul II and Archbishop Christodoulos met at the Aereopagus, where the Apostle Paul preached to Athenians 2000 years ago.
Pope John Paul II stated: "For occasions past and present when the sons and daughters of the Catholic Church have sinned by actions and omission against their Orthodox brothers and sisters, may the Lord grant us the forgiveness we beg of Him." Many Orthodox regard this as a "political" apology for the sacking of Constantinople in 1204, as well as for other issues, but it was clearly not in any way or form a religious/doctrinal apology on the part of the Roman Catholic Church.
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."
- Wikipedia:Fourth Crusade
- The Sack of Constantinople - by Nicholas A. Cooke
- 1 Nicetas Choniates: The Sack of Constantinople (1204) - from the Medieval Sourcebook
- The Cambridge Medieval History: Vol. IV-The Byzantine Empire: Part 1-Byzantium and Its Neighbours.
- Riley-Smith, Jonathan. The Crusades: A Short History. Great Britian, 1987.
- Vryonis, Speros. Byzantium and Europe. Harcourt, Brace & World, New York, c1967.
- Runciman, Steven. Byzantine Civilization. Cleveland World Publ. Co. 1965.
- Treece, Henry. The Crusades. London, 1962.
- Miller, William. The Latins in the Levant: A History of Frankish Greece 1204-1566. Cambridge, Speculum Historiale, 1908.
- Atiya, Aziz A. Crusade, Commerce and Culture. Indiana University Press, 1962.
- Hussey, J.M. The Impact of East and West 1204-1453: Latin Treachery and Byzantine Diplomacy 1204-1261, In The Byzantine World, 1961.
- Ostrogorsky, George. The Byzantine State. Transl. Joan Hussey. Rutgers, 1969.
- Schmandt, Raymond. The Fourth Crusade and the Just War Theory. (article).
- Gregoire, Henri. The Question of the Diversion of the Fourth Crusade. (article).
- Morris, Colin. Geoffrey De Villehardouin and the Conquest of Constantinople. (article).
- Folda, J. "The Fourth Crusade 1201-1203: Some Reconsiderations." in Byzantino-Slavica 26(1965),pp.227-290.
- Joinville and Villehardouin. Chronicles of the Crusades. Transl, M.R.B. Shaw. Penguin Books, 1963.
- Odo of Deuill. De Profectione Ludovici VII in Orientem (The Journey of Louis VII to the East). Transl Virginia Gingerick Berry. New York, 1948.
- Niketas Choniates. O City of Byzantium, Annals of Niketas Choniates. Detroit 1984.
- Robert de Clari. The Conquest of Constantinople. Transl. Edgar Holmes McNeal, University of Toronto Press, 1996.
- The Chronicle of Morea : a history in political verse, relating to the establishment of feudalism in Greece by the Franks in the thirteenth century. Ed. John Schmitt (1856-1906). Groningen : Bouma's Bockhuis, 1967