From the ground, a 100-hectare site just north of Italy's Venice airport looks like nothing more than rolling fields of corn and soybeans. But it's actually home to a buried Roman metropolis called Altinum, considered the precursor of ancient Venice. Now, using sophisticated aerial imagery, researchers have brought this city to life once again.
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.
Altinum was eventually abandoned entirely. Most of the ancient city's stones were stolen in the Middle Ages to be reused elsewhere. Land-reclamation efforts in the 19th century turned the area from marsh into farm fields. "Altinum is unique because it was not built upon in later times," Mozzi says. Previous archaeological excavations have focused mainly on the city's necropolis, located outside the walls; this is the first-ever glimpse of the city's layout.
Local officials are enthusiastic about the study, which will be published in tomorrow's issue of Science. "Before what Professor Mozzi has done, it was impossible to imagine the complexity and distribution of the main buildings and structures of the municipium," Margherita Tirelli, inspector of the Archaeological Superintendence of Veneto and director of the National Archaeological Museum of Altinum, writes in an e-mail.
Mozzi and his team are planning further survey work, including scans of the area with a remote-sensing technology known as LIDAR, which will help create a higher-resolution topographic map of the site. The team also plans to sample soil at the site to see whether environmental conditions, such as flooding or drought, might have contributed to Altinum's abandonment. The images will help archaeologists pinpoint the best locations for future excavation, Tirelli says: "They will help us very, very much in our future work of conserving the ancient site of Altinum. At the moment, we have a lot of hopes and plans but no money."