But Venice didn’t have enough ships. To produce the number needed meant that the city’s energy had to be focused exclusively on ship-building for a year. That meant no trade, and little income. The Franks said don’t worry about it — they will cover the expenses for the trip.
But when it came time for the troops to collect in Venice, only about 12,000 showed up, and they only had half the money. This could have spelled financial disaster for the Venetians, but, as enterprising and quick-thinking businessmen, they understood that when one door closed another one opened.
At about this time they were running into a little problem with the port city of Zara. This was a Christian city attempting to assert its independence from Venice, and the Venetians wanted the Crusaders to help them re-establish their authority. Even though the pope threatened excommunication — again, Zara was a Christian city — the Crusaders had to agree, or the Venetians would not sail.
Venice also had a problem with the Byzantine Empire, never a friend to the west. The emperor had kicked out the Venetian sales reps – mostly because the Venetians were just a little too good at their jobs and were dominating trade. There was also some question as to who the actual emperor was, and both the Crusaders and the Venetians felt that restoring the true emperor made a great excuse for an attack. Third, there was the promise that, if the rightful emperor was placed on the throne, the Orthodox Church would recognize the authority of Rome and the papacy.
So, the Crusaders agreed to raid and sack Constantinople, another Christian city. After a months’ long siege, the Crusaders broke through, and over a period of 3 days, soldiers went on a spree of violence, destruction, and looting.

The Sack of Constantinople