In 565 the Byzantine Emperor Justinian brought Venice and the Veneto under the rule of the Byzantine Empire.  The Emperor recognized that Venice could function as a valuable defense point between the Eastern and Western worlds. Further, Justininan knew the power of the Venetian fleet and desired their protection.  In order to secure the protection of Venice, the Venetians and the Emperor reached a mutually advantageous agreement concerning their political ties and responsibilities to one another: as compensation for Venice keeping her ports open and available for the use of Byzantine imperial vessels and protecting the Byzantine Empire with their own ships when called upon, Venetian merchants were awarded  protection and trading privileges throughout the Empire.[1. John Julius Norwich, A History of Venice, (New York: Alfred A. Knopf, 1982),8-9.]

In 1082, another important political agreement between Venice and the Byzantine Empire increased Venice’s economic presence and status throughout the Byzantine Empire.  In the preceding years, the Venetian fleet came to the aid of Constantinople, then under attack by the Normans.  For their service in the defeat of the Normans, the Emperor greatly awarded them in the contents of a chrysobull.  The chrysobull consisted of a variety of different items, including annual financial grants and grand titles given to Venetian citizens, but the most important clause involved the Venetian trade status throughout the Byzantine Empire. In this clause of the chrysobull, Emperor Alexius granted “Venetian merchants the right to trade in all manner of merchandise in all parts of his empire free of any charge, tax, or duty payable to his treasury,” and essentially gave the Venetians a commercial monopoly in trading ports throughout the Byzantine Empire.[2. Donald M. Nicol, Byzantium and Venice A Study in Diplomatic and Cultural Relations, (Cambridge: Cambridge University Press, 1988), 61.]

In 1171, however, the relationship between Venice and the Byzantine Empire changed.  The Byzantine Emperor falsely accused the Venetians of an attack on a Byzantine province and imprisoned nearly all the Venetian citizens in Constantinople as punishment and revenge.   Venice, outraged, demanded compensation for the false accusation.  In 1186, the Venetians and the Byzantine Empire enacted a reconciliatory agreement.  In return for financial compensation  for all Venetian losses in 1171, the Emperor demanded that three out of every four Venetian men living throughout all Byzantine territories could be conscripted into the Imperial navy.  Thus, in times of war, three-quarters of the Byzantine Imperial fleet would consist of Venetian sailors.  The Venetians wisely accepted these terms, and this deciscion would prove extremely beneficial during the Fourth Crusade.[3. John Julius Norwich, A History of Venice, (New York: Alfred A. Knopf, 1982)104 and 121.]