“Doge” from the L’Archivio di Stato di Venezia: indice generale, storico, descrittivo ed analitico (1937) by Andrea da Mosto
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.
In late Antiquity the north-east of the Italian peninsula suffered many invasions. The wars caused people to move to the safer lagoon areas, and hence to the foundation of Venice.