The events around the demise of the Exarchate of Ravenna only involved the Venetians marginally. It is nevertheless important to the history of Venice.
The Liber Pontificalis for Gregory II (715–731), recounts in great detail the conflicts between the Eastern Roman Empire and the Papacy, with repeated attempts at the life of the pope.
Venice started as a Byzantine duchy, ruled by a “dux”, but at some point, they started choosing their own dux — or doge. When, or even who, is not clear.