Archaeologists have known for decades that Altinum, a Roman trading center that thrived between the 1st and 5th centuries C.E., lay below these farm fields. Raised 2 to 3 meters above the surrounding marshy lagoon by centuries of human habitation, the city was approximately the size of Pompeii. Its history could stretch back to the Bronze Age, and it dominated the region for at least 600 years before it became a part of the Roman Empire.
But all traces of Altinum's buildings have long since disappeared, either stolen as building material or swamped by rising water levels in the surrounding lagoon. So how to map a city with no visible ruins? In July 2007, during a severe drought, Paolo Mozzi, a geomorphologist at the University of Padua in Italy, and his team took aerial photos of the site in several wavelengths of visible light and in near-infrared, with a resolution of half a meter.
When the images were processed to tease out subtle variations in plant water stress, a buried metropolis emerged. The researchers discovered that the crops planted on the land were in different stages of ripening, thanks to differences in the amount of water in the soil. Lighter crops traced the outlines of buildings--including a basilica, an amphitheater, a forum, and what may have been temples--buried at least 40 centimeters below the surface. To the south of the city center runs a wide strip of riper crops. They were growing above what clearly used to be a canal, an indication that Venice's Roman forebears were already incorporating waterways into their urban fabric.
In fact, Altinum's end may have been Venice's beginning. The first century Roman historian Strabo mentions Altinum's importance: Its location near both heavily traveled sea routes and along roads running north to the edges of the Roman Empire made it a critical mercantile center. But as waves of barbarians invaded, Altinum was a ripe target. Finally, in the 7th century C.E., a Lombard invasion pushed the city's beleaguered residents onto the defensible islands of the Venice lagoon.
This is what Strabo had to say (5.1):
These cities, then, are situated considerably above the marshes; and near them is Patavium, the best of all the cities in that part of the country, since this city by recent census,23 so it is said, had five hundred knights, and, besides, in ancient times used to send forth an army of one hundred and twenty thousand. And the quantities of manufactured goods which Patavium sends to Rome to market — clothing of all sorts and many other things — show what a goodly store of men it has and how skilled they are in the arts. Patavium offers an inland voyage from the sea by a river which runs through the marshes, two hundred and fifty stadia from a large harbour; the harbour, like the river, is called Medoacus. The largest city in the marshes, however, is Ravenna, a city built entirely of wood24 and coursed by rivers, and it is provided with thoroughfares by means of bridges and ferries. At the tides the city receives no small portion of the sea, so that, since p315the filth is all washed out by these as well as the rivers, the city is relieved of foul air. At any rate, the place has been found to be so healthful that the rulers have given orders to feed and train the gladiators there. Now this is indeed one of the marvellous things at Ravenna, I mean the fact that the air in a marsh is harmless (compare the Egyptian Alexandria, 214where, in summer, the lake25 loses its baneful qualities by reason of the overflow of the Nile and the disappearance of the standing waters), but the behaviour of the vine is also a thing fit to marvel at; for although the marshes support it and make it fruit quickly and in great quantities, it dies within four or five years. Altinum too is in a marsh, for the portion it occupies is similar to that of Ravenna. Between the two cities is Butrium, a town belonging to Ravenna, and also Spina, which though now only a small village, long ago was a Greek city of repute.a At any rate, a treasury26 of the Spinitae is to be seen at Delphi; and everything else that history tells about them shows that they were once masters of the sea. Moreover, it is said that Spina was once situated by the sea, although at the present time the place is in the interior, about ninety stadia distant from the sea. Furthermore, it has been said that Ravenna was founded by the Thessalians; but since they could not bear the wanton outrages of the Tyrrhenians, they voluntarily took in some of the Ombrici,27 which latter still now hold the city, whereas the Thessalians themselves returned home. p317These cities, then, are for the most part surrounded by the marshes, and hence subject to inundations.
The Map of Altinum, Ancestor of Venice
Andrea Ninfo, Alessandro Fontana, Paolo Mozzi, Francesco Ferrarese
Processing and interpretation of July 2007 digital visible and near-infrared aerial photographs, coupled by a digital terrain model, has allowed for detailed reconstruction of the topography and the paleoenvironmental setting of the Roman city of Altinum, shedding new light on the far origins of Venice. Images were taken during severe dry conditions, which stressed the maize and soy crops. The city walls and doors, the street network, dwellings, theaters, amphitheater, forum, emporia, basilica, and a complex network of rivers and canals have been mapped.