Aerial imaging has many uses in this day and age, but one I would not have expected was the identification of abandoned Roman towns from the air.
A team of scientists from Padua University were able to reconstruct the streetplan of an abandoned Roman town, Altium, and published the findings in Science magazine back at the end of July. The city was sacked and burned by Attila the Hun in A.D. 452, beginning a low, slow decline. Over the centuries its inhabitants began to move down the coast and set up shop on the tactically superior islands of Venice, which is one reason we can still detect these detailed traces of Altinum today—no medieval town grew up on top of it. A serendipitous drought back in 2007 made it possible for aerial imaging to spot long-buried stones, bricks and other solid structures beneath the soil.
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.
— Curry, Andrew. “Ancient Roman City Rises Again.” ScienceNOW, 30 July 2009.
For an even better look at the city’s geography, see the indispensable Ogle Earth blog, which has overlaid the false-colour and streetplan views in Google Earth (and provides a downloadable KML file so you can see it yourself).