1A - The course of the Fourth Crusade: military preparations
Learn how the Fourth Crusade moved from a planned attack on Muslim power to attacks on Zara and Constantinople, and explain why the main expedition failed to advance its Holy Land objective.
Preparations and the debt crisis
Military preparations for the Fourth Crusade created a fleet before they produced an army able to pay for it. The agreement negotiated at Venice in 1201 covered an anticipated 33,500 men and 4,500 horses for 85,000 silver marks. Venetian construction, provisioning and commitment of war galleys made possible a major maritime expedition. These preparations were substantial, even though recruitment and payment failed to match them.
When fewer crusaders assembled at Venice in 1202, the contributions available fell short of the fixed price. Some people who had taken the cross went through other ports; others did not arrive. The leaders collected money and sought further contributions, but a debt remained. They faced the danger of losing the fleet and seeing the gathered army disperse before it reached its intended target.
Dandolo offered a way to postpone the financial crisis: assistance for Venetian objectives could allow the expedition to continue. This was leverage arising from control of transport and credit. The crusade’s barons still had to choose whether to accept it. Debt explains pressure, but does not remove responsibility for subsequent decisions.
The intended Egyptian strategy also helps explain why ships were so important. A force attacking Egypt needed maritime transport and continued supplies. The leaders’ commitment to a large Venetian fleet left them less able to change supplier or route when their estimates proved wrong. An ambitious military plan therefore increased dependence on an ally whose priorities were not identical to the pope’s.
Zara and papal authority
The first major diversion was to Zara, now Zadar, on the Adriatic coast. It was a Christian city under Hungarian authority that Venice wished to recover. The king of Hungary had himself taken the cross, making an attack especially difficult to justify as part of a crusade. Yet its conquest promised a benefit to Venice and a winter base for an army still facing unpaid debts.
The crusaders and Venetians captured Zara in November 1202. The decision was contested: some crusaders objected, and some withdrew rather than join the attack. Simon of Montfort was among those who rejected the diversion. Participation did not demonstrate unanimous agreement about what religious duty required.
Innocent III opposed attacking the Christian city, and excommunication followed its capture. The pope subsequently absolved the non-Venetian crusaders who sought pardon, while the Venetians remained under the sanction. Leaders nevertheless kept the combined expedition together. An order issued from Rome could condemn wrongdoing, but its practical effect depended on communication, compliance and whether participants believed they could continue without Venice.
Zara was therefore a turning point in the relationship between purpose and practice. The army preserved its ability to sail by using force against Christians. Some leaders treated the attack as a temporary necessity serving the future crusade; opponents saw it as a violation of the expedition’s religious basis. The disagreement helps explain how a common vow could coexist with divergent choices.
The Byzantine offer and its failure
During the winter at Zara, the exiled prince Alexios offered another route out of the expedition’s difficulties. He promised large payments, troops and support for the Holy Land expedition, together with submission of the Greek Church to Rome, if the crusaders restored his father Isaac II to the Byzantine throne. Crusader leaders could present intervention as a means of financing the original religious objective.
They sailed to Constantinople in 1203. Military pressure drove Alexios III to flee in July, and Isaac II was restored; the younger prince became co-emperor as Alexios IV. The crusaders had achieved a change of government, but it did not deliver an uncomplicated solution. Alexios IV could not meet all his promises without extraordinary demands on his subjects. Foreign troops and payments deepened local hostility, while clashes and fires worsened relations.
The emperor depended on the army that had brought him to power, while that army depended on promised funds to continue. Each side’s weakness increased the other’s frustration. In early 1204 a further palace upheaval brought Alexios V Doukas to power, and Alexios IV was killed. The restoration bargain had collapsed, leaving crusaders outside a hostile city with no satisfactory payment or agreed onward plan.
The main stages make the change in purpose visible:
| Stage | Immediate objective | Effect on the Holy Land expedition |
|---|---|---|
| Venice, 1201–02 | Secure ships and provisions | Created debt when recruitment fell short |
| Zara, 1202 | Meet Venetian needs and preserve the army | Used time and force against a Christian city |
| Constantinople, 1203 | Restore a claimant in return for support | Made onward movement depend on unstable Byzantine politics |
| Constantinople, 1204 | Defeat the new regime and secure a settlement | Replaced the intended eastern campaign with conquest and partition |
This sequence supports an explanation of cumulative diversion. It does not mean that decisions were accidental or harmless: leaders repeatedly chose to continue intervention as the original objective became more remote.
Conquest without a Muslim campaign
In April 1204 the crusaders and Venetians captured Constantinople and subjected it to extensive looting and violence. Churches and sacred objects were not protected by the city’s Christian identity. Latin leaders then established a Latin Empire, with Baldwin of Flanders as emperor, and divided territory and privileges. Venice acquired strategically valuable positions and commercial advantages.
The main expedition never launched its planned attack on Egypt or recovered Jerusalem. Soldiers, ships, money and attention were absorbed by the Byzantine intervention and the effort to retain conquests. Some crusaders had gone separately to the Holy Land, but their presence did not turn the Constantinople expedition into a successful campaign against Muslim power. The Ayyubid centres in Egypt and Syria escaped the major attack that the original strategy had envisaged.
This failure was not a battlefield defeat by a Muslim army. It was a failure to direct the expedition’s military capacity towards Muslim opponents at all. Religious ideals continued to be invoked, and some participants expected intervention to make later crusading possible. Judging the outcome requires comparing those claims with where force and resources were actually used.
Venetian interests explain the pressure towards Zara and the benefits Venice gained. Byzantine instability explains the opportunity at Constantinople. Debt and failed promises connect the diversions. Crusader ambition, leadership choices and the limits of papal control explain why those opportunities were pursued. A single-cause account cannot adequately explain every stage.
The collected Fourth Crusade accounts include different descriptions of the debt, dissent and diversion. Villehardouin participated in the leadership; Robert of Clari wrote from a less privileged position. Their differences are a reason to test explanations carefully, rather than to invent a unanimous crusader intention.