It seems counterintuitive, but sometimes archaeologists can learn more by not digging up the past. In fact, noninvasive methods—including lasers, ground-penetrating radar, and drone photography—are changing the way they do their work.
One of the latest examples: a project at Ammaia, in southern Portugal, where researchers have been able to create detailed, three-dimensional illustrations of a now-underground Roman village in its heyday.
Data from the site show that the town flourished in the first century A.D.—at its peak it was home to more than 2,000 inhabitants—but gradually declined in the fourth century. By the Middle Ages it was abandoned.
Using a variety of noninvasive techniques, an international team of researchers has been able to identify different phases of the town’s construction, from Augustan times onward.
The result? A first-of-its-kind video of what a walk through the town would have looked like, stitched together via different kinds of data.
Ammaia is one of the first projects in the world to fully integrate cutting-edge fieldwork techniques with visualization software in order to reveal an invisible heritage. But if the noninvasive trend continues apace, it certainly won’t be the last.
Looking Without Touching
Not all noninvasive techniques are new. Aerial photography, for instance, has been a mainstay of archaeological research since the 1970s.
But over the past decade, techniques and technologies have advanced in both depth and breadth, letting archaeologists see more detail beneath the ground, over a wider area.
Keeping the past buried has its obvious benefits. Digging—even careful, scientific digging—can destroy some of the features that are underground. And artifacts that are exposed are vulnerable to a variety of environmental predations.
“The future of preservation is to refrain from excavation,” says Cristina Corsi, an archaeologist at the University of Cassino in Italy and coordinator of the Radio-Past Project, which broadcast the digital and traditional excavations at Ammaia.
Corsi says that when Pompeii’s House of the Gladiators collapsed in 2010, many of her colleagues felt a strange sensation—relief, because the incident could mean that other sites will be saved from the same fate.
Many people aren’t aware that excavated archaeological structures need constant care, and that environmental conditions today—which are often very different from the climate in which relics were preserved—makes it likely that they’ll crumble.
“For [every event like the House of Gladiators collapse] that’s in the news, hundreds happen each day at archaeological sites,” Corsi told an audience last month at an American Association for the Advancement of Science meeting in San Jose, California.
Even in Rome, where cultural preservation is a well-funded priority, sites can be vulnerable. Pieces of the Colosseum recently tumbled free, for instance, and partial collapses have occurred in the plastering on Roman aqueducts, ceilings in the Domus Aurea, and several structures on the Palatine Hill.
A Closer Look
Ammaia sits in a Portuguese nature reserve, which means it can’t be dug up. So when the researchers—who hail from Portugal, Belgium, Slovenia, the Netherlands, the U.K., and Germany—began working in 2009, they had to do so in a noninvasive way.
Their first step was to create a topographic map, and then to use Helikites—helium balloons crossed with kites—to get a view of the area, including a quarry that Romans used for construction materials.
The next step was a geomagnetic survey. Covering more than 37 acres (15 hectares), it revealed almost the full plan of the town, plus many elements of Ammaia’s suburbs, including roads, cemeteries, and industrial sectors. It also showed stone blocks used for heating—probably ovens, kilns, or objects to heat water for the town’s baths.
Then the researchers turned to ground-penetrating radar, which shoots electromagnetic pulses into the earth and registers the signals reflected by underground structures. That makes it possible to create images of surfaces below street pavements and airport tarmacs, among other hard-to-reach locations.
At Ammaia, the radar survey of the forum and its adjacent baths revealed details like drains and columns within buildings.
Then and Now
Noninvasive methods are being used more and more often these days, in more and more places. But they’re hardly ubiquitous.
In fact, adoption of noninvasive methods varies widely, even within countries, says Axel Posluschny, an archaeologist and manager for ArcheoLandscape Europe. Some governments are reluctant to give researchers access to data-packed aerial photos—usually the starting place for noninvasive archeology—for fear that they could be used for other purposes.
Nevertheless, over the past several decades, noninvasive methods have begun making their way into archaeological training—meaning the next generation of archaeologists will likely know how to use these techniques.
At places like Leiden University in the Netherlands, which is implementing an intensive training program for noninvasive archaeology, students are being taught remote-sensing techniques.
“Usually,” says Posluschny, “these courses consist of both a theoretical [part] and a practical part—either hands-on experience or a field school—related to an ongoing research prospect.”
At the same time, existing technologies are improving. Lidar scans, for instance, are made using red-light lasers, which don’t work underwater because liquid absorbs red light. But NASA and an Austrian firm are developing a lidar green-light laser that will soon be able to see clearly in shallow water.
Going forward, a combination of traditional and noninvasive techniques may be the best way to gather data.
As for cost, digital methods are generally cheaper than traditional ones (provided the researchers using them have the right training). Software to stitch together data from diverse sources is usually free. And as drone technology continues to advance—the latest devices have more sensors than ever before—data collection will speed up and aerial photography will become even cheaper and easier.
Still, says Posluschny, traditional methods continue to play an important role. For one thing, it’s still not possible to date objects without digging them up. For another, because older objects are buried deeper than newer ones, it’s harder to create a digital chronology for a site than to use traditional digging methods.
“Excavating gives a different kind of information,” says Posluschny. “Aerial photos, lidar data visualizations, or geophysical surveys usually give information about the shape and the size of [buried] archaeological sites.”
Going forward, a combination of traditional and noninvasive techniques may be the best way to gather data. For instance, remote-sensing information—great for covering large areas and landscapes with minimal work—is now being used to pinpoint the best places to perform minimal, targeted excavations.
The Future of Seeing the Past
In some ways, it’s becoming easier than ever to connect people to the past. Smartphones and tablets can already display compelling, three-dimensional explorations in real time.
But for some people, there’s no replacing the real thing.
“Among tourists [looking at a site remotely], you have the impression that they feel robbed [of] the possibility to touch and see monuments,” said Corsi.
In some places, however, that’s not an option. Many cities, especially in Europe, have long histories of building on top of archaeological sites. In those cases, noninvasive research techniques may be the only way to dig into former times.
Cornelius Meyer, a geophysicist and managing director of the geo-prospecting firm Eastern Atlas, based in Berlin, says it’s now possible to see beneath many places—airports, roads, church floors, town squares—that were inaccessible in the past. And, he says, “we still have a lot of unexplored archeological sites” that are primed for a digital discovery.
As noninvasive research methods grow more prevalent, the expense and danger of disturbing ancient sites may itself become a relic of the past.