The Exarchate of Ravenna was an ad hoc organisation of the Byzantine dominions in Italy, established c.584, in the face of the Lombard invasion and gradual conquest of much of the Italian peninsula.
The name Venice is from the ancient tribe of the Veneti, whose lands became a Roman province, with the name of “Venetia et Histria”
Venice was an independent state for almost a millennium, but it might note have been. It all hinged on a single battle fought in the Venetian lagoon in 810.