Venetia was a Byzantine ducatus, and part of the Exarchate of Ravenna, until it was conquered by the Lombards. The coastal parts of Venetia remained Byzantine, and was the origin of later Republic of Venice.
Following the Lombard invasion and conquest of Venetia, a part of the Venetian population of the mainland cities fled or left for the settlements in the nearby lagoons.
The Lombard invasion of Byzantine Italy in 568 was a pivotal event in Venetian history, as it kicked off the movement towards a distinct Venetian society, culture and, ultimately, state.