However, a sequence of economic and political events culminated in the Crusader army's 1202 siege of Zara and the 1204 sack of Constantinople, rather than the conquest of Egypt as originally planned.

This led to the Partitio terrarum imperii Romaniae or the partition of the Byzantine Empire by the Crusaders and their Venetian allies leading to a period known as Frankokratia, or "Rule of the Franks" in Greek.

In lieu of payment, the Venetian Doge Enrico Dandolo proposed that the Crusaders back him in attacking the rebellious city of Zadar (Zara) on the eastern Adriatic coast.

This made the empire, once eventually restored, both territorially diminished and vulnerable to invasions from the expanding Ottomans in the following centuries, to which the Byzantines ultimately succumbed in 1453.

Rather than return it to the Empire (and realizing his inability to govern it), he gave the island to Guy of Lusignan, the former king of Jerusalem, who lost the crown to a former Eastern Roman ally, Conrad of Montferrat.

The truce preserved the status quo: Jaffa remained in Ayyubid hands, but its destroyed fortifications could not be rebuilt; Beirut was left to the crusaders; and Sidon was placed under a revenue-sharing condominium.

Almost alone amongst major medieval urban centres, it had retained the civic structures, public baths, forums, monuments, and aqueducts of classical Rome in working form.

[8] Its planned location made Constantinople not only the capital of the surviving eastern part of the Roman Empire but also a commercial centre that dominated trade routes from the Mediterranean to the Black Sea,[9] China, India and Persia.

[12][13] Pope Innocent III succeeded to the papacy in January 1198, and the preaching of a new crusade became the prime goal of his pontificate, expounded in his bull Post miserabile.

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.

Other notable groups came from the Holy Roman Empire, including the men under Martin, abbot of Pairis Abbey and Bishop Conrad of Halberstadt, together in alliance with the Venetian soldiers and sailors led by the doge, Enrico Dandolo.

Many of the crusaders were opposed to attacking Zara, and some, including a force led by the elder Simon V de Montfort, refused to participate altogether and returned home or went to the Holy Land on their own.

[20] In 1202, Pope Innocent III, despite wanting to secure papal authority over the Roman Orthodox Church, forbade the crusaders of Western Christendom from committing any atrocious acts against their Christian neighbours.

According to the Chronicle of Novgorod Doge Enrico Dandolo had been blinded by the Emperor Manuel I Komnenos the Great while part of an embassy to Constantinople in 1171, and accordingly held personal enmity towards the Byzantines.

The citizens of Constantinople were not concerned with the cause of the deposed emperor and his exiled son; hereditary right of succession had never been adopted by the empire and a palace coup between brothers was not considered illegitimate in the way it would have been in the West.

[48] The unforced retreat and the effects of the fire greatly damaged morale, and the disgraced Alexios III abandoned his subjects, slipping out of the city and fleeing to Mosynopolis in Thrace.

In order to cover their retreat the Westerners instigated the "Great Fire", which burnt from 19 to 21 August, destroying a large part of Constantinople and leaving an estimated 100,000 homeless.

A strong northern wind aided the Venetian ships in coming close to the walls, and after a short battle approximately seventy crusaders managed to enter the city.

The remaining Anglo-Saxon "axe bearers" had been amongst the most effective of the city's defenders, but they now attempted to negotiate higher wages from their Byzantine employers, before dispersing or surrendering.

[56][57] The eyewitness accounts of Niketas Choniates, Geoffrey of Villehardouin, Robert of Clari, and the anonymous Latin author of the Devastatio Constantinopolitana all accuse the crusaders of egregious rapacity.

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.

Villehardouin, however, regarded those who went to the Holy Land as deserters of the main army and its leadership and he may have exaggerated their number in order to magnify the accomplishments of the minority that besieged Constantinople.

The force was so small that King Aimery of Jerusalem refused to break his truce with the Ayyubids to allow them to go to war, despite the pleas of Renard, who was fulfilling the crusading vow of the late Count Theobald III of Champagne and possessed ample funds.

Upon his recovery in March 1203, he took ship in southern Italy and travelled directly to the Holy Land with many others who had remained behind, including Rotrou de Montfort and Yves of La Jaille.

According to the Devastatio Constantinopolitana, after the decision was made at Zara to place Alexios IV on the throne of Constantinople, the leaders of the crusade granted permission for about 1,000 men to leave and find their own way to the Holy Land.

O City, consumed by fire..." Several prominent Crusaders, including Enguerrand III, Lord of Coucy, Simon de Montfort, 5th Earl of Leicester and Guy of Vaux-de-Cernay, among others, disagreed with the attacks on Zara and Constantinople and refused to take part in them.

It was not enough for them [the Latins] to empty the imperial treasuries and to plunder the spoils of princes and lesser folk, but rather they extended their hands to church treasuries and, what was more serious, to their possessions, even ripping away silver tablets from altars and breaking them into pieces among themselves, violating sacristies and crosses, and carrying away relics.Historian Robert Lee Wolff interprets the two letters from Innocent III as a sign of the Pope's "early spirit of understanding for the Greeks".

"[90] According to historian Martin Arbagi, "The diversion of the Fourth Crusade in 1204 was one of the great atrocities of medieval history, and Pope Innocent III placed most of the blame on Venice".

[92] Constantinople was considered as a bastion of Christianity that defended Europe from Muslim invasion, and the Fourth Crusade's sack of the city dealt an irreparable blow to this eastern bulwark.

In 2001, he wrote to Christodoulos, Archbishop of Athens, "It is tragic that the assailants, who set out to secure free access for Christians to the Holy Land, turned against their brothers in the faith.