On this day 805 years ago, the Fourth Crusade invaded and conquered Constantinople in a thoroughly disgraceful manner. The Fourth Crusade had originally been planned with the aim of invading Egypt, and using that as a route to recapture Jerusalem from the Muslims. Interest in crusades against the Muslims had faded after the Third Crusade, but Pope Innocent III sought to raise up a new crusade after he became pope in 1198.
A crusading army was organised in 1199, and eventually in 1201 the city of Venice agreed to build numerous ships and train sailors sufficient to transport an army of 4500 knights and horses, 9000 squires and 20,000 foot soldiers to Egypt, at a price of 85,000 silver marks. The ships were completed, but the number of crusaders who arrived in Venice was only 12,000, and they could afford to pay only 51,000 silver marks, leaving themselves impoverished.
Thereafter the crusade became a matter of trying to find the balance of funds, and so instead of sailing for Egypt, the crusaders agreed to help a claimant to the Byzantine throne in exchange for a payment which would include 200,000 silver marks and 10,000 men to assist in the crusade. This led eventually to the capture of Constantinople in 1204, during which the crusaders looted everything they could find. Almost none of the crusaders ever made it to Palestine, and the event left an enduring legacy of bitterness between the Greek Orthodox church and the Roman Catholic church.