From the ancient catacombs to modern metros, people have always moved underground for short periods of time. But did entire societies of people live underground? Yes, but historically only in emergencies and when they had no other choice. However, in recent decades, the situation has begun to change.
"The main thing to know about underground space is that we don't belong there. Biologically, physiologically, our bodies are simply not designed for life underground," says Will Hunt, author of Underground: A Human History of the Worlds Beneath Our Feet (Random House, 2019).
"And yet there are times when we go underground."
Throughout history, people have temporarily lived underground for various reasons. If there were no materials to build houses, they dug underground dwellings, Hunt told Live Science.
In places with extreme climates, people went underground in the summer so as not to freeze, and in the winter to keep warm. There was also a safe place underground to hide from enemies.
For example, the ancient people built the famous underground cities in Cappadocia in the territory of modern Turkey for protection from bad weather and war.
“Geographically, they were in a very strategic location,” says Hunt. "They were constantly attacked."
During emergencies, residents went underground, but did not stay there for long, perhaps for several weeks.
One of the largest underground cities in Cappadocia is Derinkuyu, which dates from around the 7th or 8th century and could have accommodated about 20,000 people, according to Atlas Obscura.
Geophysicists have determined that another newly discovered city in the region covers an area of 5 million square feet (460,000 square meters) and may be 371 feet (113 m) deep, National Geographic reports. If true, then the newly discovered city of Cappadocia would be about a third larger than Derinkuyu.
The underground cities of Cappadocia are "an architectural marvel," Hunt said. The wells plunged deep into the water table. The holes leading to the surface served as ventilation shafts. Defensive structures - including the large round stones that the ancients rolled out before entering the city - separated those inside from the invaders on the surface.
However, not all underground dwellings were as complex as in Cappadocia. Humans also lived in natural and man-made caves, Hunt noted. Constructed caves can be found wherever there is suitable geology - for example, stone hills made of flaky rock, soft volcanic rock that is easy to dig.
“They are very common,” he said. "People are creating cave dwellings all over the world."
Even in modern Australia, in a city called Coober Pedy, about half of the population lives in dugouts, or burrows carved into the hillsides, according to the Smithsonian magazine.
Many marginalized segments of the population have found refuge underground in the abandoned infrastructure of modern cities.
These "mole people" are fewer in New York since the 1980s, but perhaps more than 1,000 homeless people live in tunnels underneath the city's streets, Hunt says. Many homeless people also live in the tunnels under Las Vegas. And in Bucharest, Romania, there are large communities of homeless orphans living under the streets.
As more and more people move to cities, more and more city dwellers can move underground. Cities like Singapore are exploring the possibility of building underground buildings.
According to Yoon Hee Lee, an assistant professor of psychology at the University of Nottingham in Malaysia who studies the psychology of being underground, the technology needed to do this already exists. The challenge is convincing people to move underground.
In fact, being underground does not yet cause negative psychological effects as long as the lighting, room size, ceiling heights and other physical characteristics of the environment match those on the ground, Lee says.
For example, technologies such as light wells, which allow natural sunlight to illuminate underground spaces with materials such as reflective paint, can combat depression caused by lack of sunlight. People may feel isolated from their colleagues on the surface, and they may feel a lack of control, but these feelings are quite surmountable, Lee said.
but people still don't like the idea of living underground.
Either way, Lee believes that people around the world will begin to transition to a new level of life soon, inspired by places that are blazing a trail, such as RÉSO, an underground city in Montreal, Canada that is over 20 miles long and includes shopping malls. offices, hotels and schools.
"It is quite possible that we will go underground soon… For at least 30 years there will be more underground jobs, more underground entertainment venues,”she said.