An ancient "maze of tunnels" sits quietly underneath the city of Rome, but they could be a safety hazard.
In 2011 there were 44 reports of portions of a street or structure collapsing into theses underground quarries, LiveScience reported. In 2013 there were 83 reports of similar incidents.
Researchers are working to map out the underground tunnels, and pinpoint the most vulnerable spots in an effort to prevent the city from crumbling into the underground abyss.
Some Roman citizens have even patched up problem areas themselves.
"The most common way is to take some big plastic bags and fill them with cement and stick them in the holes," George Mason University geoscientists Giuseppina Kysar Mattietti told LiveScience.
At the time they were built the quarry tunnels were purposely made narrow enough to support the ground above, but time and weather have started to break them down. The volcanic rock that makes up the tunnels begins to degrade when it is exposed to air.
Humans also contributed to the problem by widening the tunnels in later years in order to build structures above.
The tunnels have been used for a number of purposes over the centuries such as catacombs, bomb shelters, and a sewer system.
Romans have long-forgotten the true extent of the underground world.
"Since they weren't serving any use, people tend to forget what can be a problem," Kysar Mattietti told LiveScience.
The research team is using laser 3D scanning search for areas of the tunnels that are in danger of collapsing. The team also sometimes enters the tunnels through manholes if they are sure it's secure.
"There might be cracks, so they will be showing as veins almost, or openings, so we map the openings and map any kind of detachment," Kysar Mattietti said. "It's interesting, because at times when you are down there, you can hear people on top."
Once the team identifies unstable areas experts repair it by filling the entire tunnel with mortar.
"A crack never stops on its own," Kysar Mattietti told LiveScience. "It always gets bigger."
