Considered the predecessor of Venice, the city of Altinum is located near Venice's famous Grand Canal.
"Altinum plays a major role in Venice's history -- it was one of the richest Roman settlements but inhabitants fled before the advance of the armies of Attila the Hun. Then as water levels rose, the abandoned city sank into the lagoon. Its walls remain covered by fields today. And this is why the ancient city has remained undiscovered for such a long time."
Thanks to Archinect