In his hour of need, summer 1081, Alexius Comnenus had turned to various potential allies. Only the Venetians reacted with haste and in force because they shared the imperial fear of Norman expansion across the Adriatic. Some years earlier, in 1074, a Norman count named Amico of Giovinazzo had invaded Dalmatia and occupied the maritime cities as far south as Split. The citizens seem to have welcomed his arrival, and even requested assistance against the encroachments of the Croatian ruler Cresimir. However, the Venetians were less pleased, and the Doge Domenico Silvio (1070-84) launched an expedition to drive the Normans out. He seems to have enjoyed tacit imperial backing for the successful campaign, and on February 8, 1075, he extracted an oath from the leading citizens of four cities that they would never again grant entry to the Normans. In the extant document that records this oath the doge styled himself “Duke of Venice and Dalmatia and imperial protoproedros.”

From Paul Stephenson’s Byzantium’s Balkan Frontier: A Political Study of the Northern Balkans, 900-1204, Cambridge: Cambridge University Press, 2000, p. 168.