Loomis, Louise Ropes. The book of the popes (Liber pontificalis). New York, Columbia University Press, 1916.
A summary of the main primary sources for the early history of Venice, and where to find them.
The “Liber Pontificalis” on how a Byzantine general invited the Lombards to come and possess Italy, if they pleased.
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?