From ancient catacombs, those underground passages in which the dead were buried or their remains and bones were preserved, to the modern subway, humans have always traveled underground for brief periods of time, but have entire societies lived underground?
Yes, but historically it was only during emergencies and when there was no other option, but that has begun to change in recent decades, answers this question in his article on the science website Tara Santora, and says, "Yes."
“The important thing to know about tunnels is that we don't belong there,” says Will Hunt, author of Underground: A Human History of the Worlds Beneath Our Feet. Biologically and physiologically, our bodies are not Designed for underground life, however, there are moments when we go underground.”
Why did people live underground?
Throughout history, Hunt tells Live Science, people have lived temporarily underground for various reasons.
When there were no materials to build houses, they dug houses underground.
In places with harsh climates, people went underground in the summer to feel the cold and in the winter to stay warm.
People also resorted to living underground to protect themselves from enemies and to stay safe.
For example, the ancients built the famous underground cities of Cappadocia in what is now Turkey, to protect themselves from both war and weather.
"They were geographically in a very strategic place... they were constantly under attack," Hunt says.
So residents took refuge underground during emergencies, but they didn't stay there for long, maybe weeks at a time.
The largest underground cities
One of the largest underground cities in Cappadocia is Derinkuyu, which dates back to around the seventh or eighth century and can house about 20,000 people, according to Atlas Obscura.
Geophysics also recently discovered another city in the region that spans an area of 460,000 square meters and may be up to 113 meters deep, according to National Geographic.
If this is true, then the newly found city would be about a third larger than Derinkuyu.
Hunt says Cappadocia's underground cities are an "architectural marvel".
Wells have sunk deep into the groundwater.
The holes leading to the roof served as ventilation shafts.
Layers of protection, including large round stones that these ancients rolled in front of the city's entrances, separate those on the inside from the invaders on the surface.
Throughout history, people lived temporarily underground (Getty Images)
Living underground in the modern era
Not all subterranean dwellings were as complex as those in Cappadocia.
People also lived in natural and man-made caves.
Constructed caves can be found anywhere geologically suitable, such as stone mounds made of tuff, a soft, easy-to-dig volcanic rock.
It's very common to find people making caves all over the world, says Hunt, even in modern Australia, in a town called Coober Pedy, where about half of its residents live in "bunkers," or pits dug into the sides of hills, according to Smithsonian Magazine.
On the other hand, we notice that many marginalized people find shelter underground in the abandoned infrastructure of modern cities.
There are fewer of these marginalized people in New York than in the 1980s, Hunt says, yet perhaps more than 1,000 people live without a home in tunnels under the city's streets.
Many homeless people live in tunnels under Las Vegas, and large communities of orphans live under the streets in Bucharest, Romania.
More city dwellers may move underground (Getty Images)
Persuading people to move underground
As more people go to live in cities, more city dwellers may move underground.
Countries such as Singapore are exploring options for downward-facing construction into the ground.
The technology to do this already exists, says Eun Hee Lee, an assistant professor of psychology at the University of Nottingham's Malaysia who studies the psychology of staying underground.
The challenge is to convince people to move underground.
She tells me, in fact, that living underground has not yet been proven to cause negative psychological effects, as long as the lighting, room size, ceiling height, and other physical features of the setting correspond to what is above ground.
For example, technology such as lightwells, which allow natural sunlight to illuminate underground spaces using materials such as reflective coatings, can combat depression caused by a lack of sunlight.
She tells me that people may feel isolated from their peers on the surface, and may feel out of control, but these feelings are manageable.
However, people still hate the idea of living underground.
Rissot is an underground city in Montreal, Canada, with a length of more than 32 kilometers (Getty Images)
Lee also believes that people around the world will soon start moving underground, influenced by places that have paved the way such as RÉSO, an underground city in Montreal, Canada that is more than 32 kilometers long and includes shopping malls, offices, hotels and schools.
"Realistically, we'll be going underground soon," she says. "In at least 30 years there will be more work environments and fun places underground. It's coming, and it's not just an idea."