Explain why ancient civilizations built underground cities.

To protect oneself against enemy attacks.

The ancients quickly understood that building underground was super practical for avoiding enemy invasions. Hidden beneath the surface, these cities became almost invisible from the outside, which represented a huge strategic advantage. The entrances were narrow and discreet, easy to defend and trap. Inside, labyrinthine galleries complicated the task for invaders, forcing them to progress slowly and becoming vulnerable to counterattacks. Some cities, like Derinkuyu in Turkey, even had giant rolling stones to immediately block entrances in case of danger. Another nice bonus: being underground effectively protected against siege weapons such as catapults, fires, or enemy arrows.

To adapt to extreme climate constraints

In certain regions with particularly harsh climates, temperatures could shift from one extreme to another quickly. Living underground provided a stable and constant temperature, ideal for escaping the stifling heat in summer and the freezing cold of nights or winter. These underground cities functioned as a kind of natural insulation, simply taking advantage of the thermal properties of the ground. Not a bad system for living comfortably without having to deal with the whims of the weather.

To store food safely.

In ancient times, it was not easy to keep food fresh for long. Underground was a good solution: constant temperature and natural freshness ensured. Underground cities had reservoirs and silos buried where grains, olive oil, wine, and other goods remained edible and protected from rodents or insects. Without our modern fridges, going underground was clearly the most practical way to ensure safety and avoid food waste. Some civilizations even went so far as to create rooms entirely dedicated to preservation with natural insulation to guarantee optimal conditions year-round.

For spiritual or religious reasons

Some ancient civilizations viewed the underground world as a sacred space, linked to gods, ancestors, or even the afterlife. Building underground allowed people to be closer to these spiritual powers. For example, they would create caves or tunnels to carry out initiation rites, prayers, or funeral ceremonies. Going underground thus became a kind of symbolic journey to an invisible, mystical world, where the boundary between the living and the dead was thinner. Sometimes these places represented a retreat for spiritual reflection, where one could meditate in peace, away from the world above.

To efficiently exploit underground natural resources

In some regions, the subsoil is naturally rich in useful resources: groundwater, minerals, gemstones, or even salt. Building underground allowed the ancients to benefit from direct access to these treasures without having to constantly make trips to the surface. Cities like Derinkuyu in Turkey thus benefit from significant groundwater supplies, essential for the community to hydrate, irrigate crops, or maintain economic activity. Others extracted directly from the rock layers the building materials needed for expanding and reinforcing underground galleries and dwellings. These cities are, in a way, ultra-optimized systems, where access to subsoil resources was done on-site, at a lower cost and requiring minimal collective effort.