What unearthing ancient cities teaches us about exploring outer space

Urban ruins line a quiet thoroughfare in the northern reaches of Pompeii. Tall grass and sunflowers push through formerly tiled atrium floors, and murals, once brightly painted with scenes from Roman mythology, have faded to a few streaks of red on gray-and-brown bricks.

Time and exposure have worn them down, but ­archaeology itself has been somewhat cruel to these relics. Eager treasure hunters of the 18th and 19th centuries often dug into the earth without much concern for what they destroyed as long as they found statues, gold, or other booty. Upper stories of buildings that hadn’t been demolished by Mount Vesuvius’ hail of volcanic debris in 79 A.D. were wrecked by picks and shovels. Folks searching for loot in the wealthier southern neighborhoods of this city piled loose dirt on top of the still-buried northern blocks, creating an unstable, muddy mound of soil, bricks, pottery fragments, and other discarded artifacts.

Farther along the strip, there’s an area where those centuries-gone hunters heaped their debris. In 2010, portions of a nearby ancient athletic training facility—the “House of the Gladiators”—collapsed due to neglect, triggering the Pompeii Archaeological Park to conduct both an excavation and a rescue operation. Surrounded by scaffolding and dotted with wheelbarrows and hard hats alongside deep holes in the ground, the place looks more like a construction site than a dig. Mounds of old detritus have started to erode rapidly, threatening to make the streets and homes still below ground even more inaccessible. The effort will reveal new parts of the city, and will repair damage from previous excavations. It’s part of a larger, parkwide initiative, funded by some 100 million euros from the European Union and Italian governments, to shore up Pompeii against erosion, weather, and ill repair.

Losing Pompeii would mean losing one of the best-known and preserved relics of the Roman Empire. Unlike ruins that have long been exposed to the elements, much of this seaside destination remains as it was when ­Vesuvius erupted and entombed it in about 20 feet of hot ash. Today, the 163-acre site hosts 3 million visitors annually. People come for a glimpse of the ancient past, fossilized by a terrifying disaster that killed some 2,000 people—roughly one-fifth of Pompeii, as well as residents in the nearby towns of Herculaneum and Stabiae.

What these visitors don’t realize, as they munch on fried pizza and don tinfoil Roman helmets, is that they’re also witnessing the history of archaeological science. Diggers first excavated the city almost 300 years ago, at the behest of the antiquity-obsessed Sicilian King Charles VII; major digs starting in 1748 uncovered the town’s enormous amphitheater, and later a plaque identifying the place as Pompeii. By the 1860s, researchers had unearthed much of the burg, and the newly formed Italian government opened its streets to the public.

Today, a new generation of investigators is using modern tools to study Pompeii and other sites without wrecking them in the process. “Nondestructive techniques can help us know where and what to dig,” says Pier Matteo Barone, who teaches archaeology at the American University of Rome, and favors using portable ground-penetrating radar devices to peep through the ash before reaching for his pickax.

With added insights from high-resolution drone footage, 3D modeling, and data-​­analysis, this wave of historical explorers is painting a richer picture of long-gone life. Their methods also mirror those we’ll employ beyond this planet, when space agencies will need to probe potentially life-​­sustaining destinations like Mars or Europa without disturbing what’s already there.

Wondering if one day we might encounter the crumbling remains of a civilization on an icy moon of Jupiter, I strolled the Via di Nola during 2018’s hot, dry summer excavation season. In the evening, after the throngs of tourists thinned and the researchers laid down their trowels, the shadows around me deepened, as the high, crumbling walls that flank the old commercial street blocked out orange light from the waning sun. Two thousand years ago, this wouldn’t have been unusual; most buildings in Pompeii rose three or four stories high, submerging the narrow road in welcome shade. But these upper floors rarely survive today.

As I wandered toward the downtown temple district, and the sky continued to darken, I heard a low hum from above. I glanced up, and caught sight of a small drone swooping in low over my head. It flew in a precise switchback pattern, and I knew instantly this was not some tourist with a toy. It was the tool of an archaeologist.


The video begins at eye level above Via Stabiana, a major ­artery leading to a gate out of northwest Pompeii. From here, the ­camera-​­toting drone passes between densely packed homes that line the sunken cobblestone road, which is punctuated by tabernas, shops, laundries, and bakeries. Raised crosswalks of enormous rocks transverse the street. After a couple of blocks, the view broadens, revealing the complexity of the grid. Beneath Vesuvius’ vivid green slopes, thousands of buildings come into focus—and suddenly it’s obvious that Pompeii was once a small city as complex as any in the modern world.

“Drones are revolutionizing archaeology,” says Eric ­Poehler, an archaeologist from the University of Massachusetts at Amherst, as he and colleague Steven ­Ellis of the University of Cincinnati show me the footage on Ellis’ laptop. We’re drinking beers at a hotel bar as the pair explain how they fly everyday DJI drones with built-in 4K cameras over sites to capture 3D images. “Over the course of one programmed flight, we could produce a 4-​­gigabyte image with a resolution of 1.3 centimeters per pixel,” Poehler says, describing visuals so detailed that he can zoom in enough to examine tiny cracks in the masonry.

Now, Poehler and Ellis can consult their footage to plan more-precise digs. These high-­resolution charts become the bottom layer of a digital archive of the area, with each feature “orthorectified,” or perfectly fitted to the ­real-​world grid like a building in Google Earth. Pulling out his phone, Poehler loads the imagery into an app called ArcGIS, which is a bit like Photoshop for maps. He can create new information layers on top of the chart, allowing him to draw their discoveries onto the images as his crew digs. If Poehler and Ellis find a fast-food joint (called a taberna), they can doodle a box over it and name it. They can also layer on finer details, such as labeling bricks by their material.

The pair use a technique called photogrammetry to re-create these ancient ruins in 3D. Off-the-shelf scanning software lets them merge 2D photographs with measurements they’ve taken on-site to achieve complete environments. Over many years, Ellis and Poehler’s team has pieced together full rooms and neighborhoods; thousands of images (both old and new) of Via Stabiana now exist as a virtual model of the strip.

Drone footage and digital images, however, are helpful only above ground. More than one-quarter of the ancient metropolis remains buried. So Ellis, Poehler, and the American University’s Barone are using ground-​­penetrating radar help to fill in the gaps.

GPR is like a subterranean ultrasound. The rigs, about the size and shape of lawnmowers, contain antennas that send electromagnetic pulses into the earth and collect them after they bounce off subsurface structures. These reflections reveal the density of underground materials. Variations in the patterns show, for example, the exact place where ashy mud meets the top of a brick wall.

Though GPR has been a popular tool among archaeologists for decades (it revealed traces of what might be 60 additional buried pillars at Stonehenge, and the remains of King Richard III under a Leicester, U.K., parking lot), it’s only recently proved its worth in mapping geology like what exists in Pompeii. Despite uncertainty that the pulses would retain their fidelity through deep ash, which can impede the signals, Barone’s research has found the region quite compatible with the tech. He was pleased, he says, to discover that “you have a fast penetration of waves into volcanic sediments.”

When his team published one of the first GPR surveys of Pompeii in 2011, they focused on an unexcavated patch of land around the northern walls of the city. Studying the readout for anomalies, they detected what appeared to be two walls lining a Roman road. The tops of both were buried nearly 23 feet deep in the ash. The results were so promising that he wants his next target to be the entire city of Rome, where he could use his handheld GPR to help create an accurate map of what the place looked like millennia ago, without disturbing a single brick.

The common picture of Pompeii is one of a ­thriving beach town for vacationing soldiers and the ­Roman one-​percenters, where lavish summer villas with tiled verandas opened to ocean breezes. But archaeologists wielding these new tools provide a glimpse of proletarian life that their predecessors historically ignored. We know the names of some wealthy residents like Cicero, as well as Nero’s second wife, Poppaea Sabina. But we don’t know much about the women who planned dinner parties. We know even less about the slaves who ran errands on the sidewalks of Via di Nola. That’s why a researcher like Barone might be as excited to find a bit of pavement as his 18th-century counterparts were to find marble-lined villas.

GPR surveys like his have already upended long-held ­assumptions about the city, including the history of one of its most visited landmarks. Located on the Via Stabiana on the southern edge of town, the Quadriporticus is an enormous open-air atrium, about an acre in total, surrounded by a colonnade and dozens of small rooms. For years, investigators assumed, based on a single fresco of weapons, that it had been a gladiator barracks. Ellis and Poehler’s GPR analy­sis, however, offered a more compelling clue: About 1.5 feet below the surface sits a circular ­structure that was once the foundation for a large, central ­gazebo. The form matches ones found locally and others at outdoor markets in Rome. This suggests that the ancient square might have been filled with vendors selling fermented fish, sauces, and wine. Maybe it wasn’t a place for entertaining the rich but for feeding the masses.

The more investigators pore over their new troves of digital data, the more they’re able to add texture to the portrait of everyday life. Ellis, for instance, studied the maps he and Poehler built to count and catalog Pompeii’s 160 ­tabernas, revealing the city as a thriving center for street life. And now, thanks to chemical analy­ses, he knows what people ate in these eateries. Cesspits in two spots showed that one served meals with imported spices and many kinds of fish, while the other offered up ­Roman-​style comfort foods like sausage and cheese. “The trend is to look for the big, the mighty, the unusual,” Ellis says with a rueful smile. “What we do is look for the usual.”

Similarly, Lisa Hughes, a classics professor at the University of Calgary, is re-creating scenes from domestic life, and exploring the interactions between the women, foreigners, and slaves who would have populated it. She and her collaborators have used the popu­lar Unity developer platform (it underpins hits like Super Mario Run and Pokemon Go) and digital photographs to build a virtual-reality simulation of plays staged in the courtyard of the House of the Golden Cupids, a well-preserved home in a fashionable part of town. In the setup, players can walk through the space and experience what it was like to watch a pantomime in Nero’s reign.

Inside the simulation, which feels something like an 8-bit (but highly accurate) version of Assassin’s Creed, players enter the four-sided garden, called a peristyle, where Romans enjoyed meals alfresco. ­Guests would have reclined on couches along the perimeter to eat; performers might have begun the show on a stage in front of dramatic wall paintings of Bacchus, the god of wine and theater.

Mouse-clicking their way through the colonnaded garden, players pass between rows of manicured shrubs, en route to the central fountain. As Hughes shows off the scene, she explains that watching people “walk” through the space helps her speculate about how actual Roman aesthetes might have meandered. “We think of a 19th-century dining idea of theater, that everyone would be seated and quiet,” she says, citing what she’s been able to glean from ancient writings. “I might get up and move around,” she muses. Using her model, she can see how that could have played out: which pathways or vantage points people use, and how the changing light might affect where and when they sat.

More important, Hughes has brought to life a social tipping point in ­Roman history. Shifting social norms had allowed theater to enter the home and the realm of women. Her model is one way we can glimpse ­inside this world, and learn about life beyond the Forum.

Ground-penetrating radar in Pompeii
Ground-penetrating radar ­reveal a gazebo-like structure and other renovations below the surface of a large, public atrium. Poehler and Ellis 2014: Fig. 4, Fig. 7

In the coming decades, the noninvasive techniques we use to envision ancient civilizations on Earth could help us chart new worlds in outer space. “No nation has the right to alter a place that we are trying to understand and explore,” says Lisa Pratt, who heads NASA’s Office of Planetary Protection, which creates guidelines for the agency’s probes and landers. She encourages engineers to refine nondestructive archaeological tools like GPR and drone imaging so we’ll leave no trace as we search for signs of life on distant planets. “These are instruments that are off-the-shelf for studying Earth, but we want to get them ready for launch and deployment in other planetary environments,” she adds.

Cosmos-bound variations are already in the works. A GPR device called RIMFAX, for example, will head to the Red Planet on NASA’s Mars 2020 mission. It won’t be looking for lost civilizations there, but for a lost ecosystem. “We want to find potentially habitable environments, where there might once have been some life,” says Rebecca Ghent, a University of Toronto geoscientist who worked on the craft. The rover will explore an area scientists speculate could have once been a river delta, full of fast-flowing streams of ice melt. They’ll watch for telltale diagonal layers of sediment that hint at sand left behind by flash floods or seasonally swollen streams.

The probe is quite similar to the kind of GPR rig that Barone’s team from the American University used to see the road buried outside Pompeii’s walls. But on Mars, a single instrument will need to sweep through the range of frequencies to scan above-ground terrain and hopefully also peer as deep as 30 feet below the red surface. Ghent credits “a trick of computer processing” with allowing them to modulate the signal ­RIMFAX uses, and collect clues about Mars’ past.

The most profound lesson investigators will apply to space from a place like Pompeii, though, is how to think in deep time. Walking on 2,000-year-old streets, temporal distances collapse, bringing both the far future and distant past into focus. Hopefully our descendants could one day wander Martian cities, quietly teeming with life that survived because we took the time to study the regolith before drilling into it. Exploration is no longer a game of planting flags and grabbing loot. It’s about preserving what we find for humans (or otherworldly friends) millennia from now.

This story originally published in the Out There issue of Popular Science.