The leaders of the Fourth Crusade (1202–04) contracted with Venice to provide a fleet for transportation to the Levant. When the crusaders were unable to pay for the ships, Doge Enrico Dandolo offered transport if the crusaders were to capture Zara, a city that had rebelled years ago and was a rival to Venice. Upon the capture of Zara, the crusade was again diverted, this time to Constantinople. The capture and sacking of Constantinople has been described as one of the most profitable and disgraceful sacks of a city in history.

The Venetians claimed much of the plunder, including the famous four bronze horses that were brought back to adorn St Mark's Basilica. Furthermore, in the subsequent partition of the Byzantine lands, Venice gained a great deal of territory in the Aegean Sea, theoretically amounting to three-eighths of the Byzantine Empire. It also acquired the islands of Crete (Candia) and Euboea (Negroponte); the present core city of Chania on Crete is largely of Venetian construction, built atop the ruins of the ancient city of Cydonia.