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 Kingdom of the Lombards played a major role in early Venetian history, as it was the Lombard invasion of Italy in 568 which started the formation of later Venice.
Why did the Lombards decide to invade Byzantine Italy in 568? A popular story was the Byzantine general Narses, who had just retaken Italy for the empire, invited them. Was Narses a traitor to the empire?