Modern-day Venice sits on islands in the Laguna Veneta, which is separated by barrier islands from the Adriatic Sea. (See a Venice map.)
Although it's miles away from Altinum, the study authors consider the mainland city to have been an ancestor of Venice.
Scholars believe that Altinum's residents fled their home during barbarian invasions in the fifth to seventh centuries A.D. and colonized the northern lagoon islands.
Records show, for example, that Altinum's bishop left for the island of Torcello in A.D. 639.
A few centuries later, Venice emerged from the dispersed islands in the central lagoon.
"Our point on the connection between Altinum and Venice is the movement of these people from the mainland out to living in the islands," Mozzi said.
"How can they do that? Because they were already very adapted to the lagoon," which became a safe refuge from less water-savvy attackers.
Experts not affiliated with the research agreed that the new map of Altinum is a tremendous advance for understanding the little-known city.
For instance, the survey offers firm evidence that Altinum was a classic Roman port similar to the nearby ancient cities of Ravenna and Aquileia.
However, several experts emphasized that the city's link to Venice is complex.
Rupert Housley, a geographer at Royal Holloway, University of London, is studying how Venice took root at the heart of a lagoon.
The aerial photography alone can't back up the notion that Altinum was particularly well adapted to lagoon living, Housley said.
"Certainly the residents of Altinum may well have contributed to peopling of the islands, probably along with the other coastal towns," he commented via email.
But from the map there appears to be nothing especially unique about Altinum compared with other nearby Roman ports, he noted.
Albert Ammerman, an archaeologist at Colgate University in Hamilton, New York, said Venice arose organically from migrating residents of several coastal cities, including Altinum.
All of those cities' people, he said, "knew how to live in this aquatic environment. They had all the skills and local knowledge, so it wasn't very difficult for them to go out there" and survive.
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