Fourth Crusade (1202 – 1204)
The Fourth Crusade was launched after a call of Pope Innocent III in 1198 but there was little interest in Europe for another Crusade against the Muslims after the Third Crusade. The Crusader army was gathered by Boniface I, Marquess of Montferrat in northern France in 1199 but his forces were in first place motivated by their own interests.
In 1201, the Crusaders reached an agreement with Venice to transport them to the Holy Land and to provide supply for 85,000 silver marks. In return for its participation in the Crusade Venice also demanded its representatives in the leadership and half of all conquered lands. However, when Crusaders (primarily led by French and Flemish nobles) gathered in Venice they did not have the necessary sum to pay Venice for its services. For that reason Venice gave the Crusaders two options, either to pay the demanded sum or to capture the Dalmatian city of Zara (Zadar) from Hungary. The Crusaders had chosen the latter option and thus helped Venice to establish its supremacy in the Adriatic region.
Pope Innocent III discontented with the course of the Crusade excommunicated the whole expedition but he later changed his mind. Shortly afterwards the Crusaders responded to an appeal of the Byzantine Prince, Alexios IV Angelos (or Alexius IV Angelus) to help him depose his uncle Alexios III and restore his father Isaac II Angelos in return for 200,000 silver marks, supply and troops. The Crusaders captured Constantinople in 1203. Isaac II Angelos and Alexios IV were made co-emperors but they could not pay the Crusaders because their predecessor took the state treasury. For that reason the Crusaders and Venetians decided to capture and sack Constantinople. Thus the Fourth Crusade ended with the fall of Constantinople in April 1204 without even reaching the Holy Land.