Welcome to Rome, where every year more streets and parts of buildings are collapsing into ancient passages that lurk half-forgotten underground. The city's proposed fix: map the labyrinth, detect the weakest spots with 3D scanning, and seal off the worst offenders, LiveScience reports. Successful or not, it may improve on the current approach—of Romans doing the handywork themselves. "The most common way is to take some big plastic bags and fill them with cement and stick them in the holes," says geoscientist Kysar Mattietti.
The tunnels date back to the first Romans, who carved out the area's underground Volcanic rock for building blocks. When the city spread out over the quarries, Romans figured the tunnels would last—not realizing that rock weathers when exposed to air, and later generations would keep digging for more rock. Now some tunnels are so close to collapse that you can actually hear people walking above. And researchers doing the mapping are finding cracks that snake out along passage halls and ceilings. "A crack never stops on its own," says Mattietti. "It always gets bigger."