A huge ancient stone city buried for thousands of years in northern China has just become even more mysterious. Archaeologists working at the Houchengzui Stone City in Inner Mongolia have uncovered a hidden underground tunnel network dating back roughly 4,300 to 4,500 years. The tunnels were reportedly hidden beneath one of the largest and most heavily defended early stone cities ever found in the region. At first glance, the site already looked impressive enough with massive walls, defensive gates, and layers of protection everywhere. Then researchers discovered something underneath it all.Experts say the tunnels may have been used for both defence and movement inside the city, which raises all kinds of questions about how advanced these early communities really were. Some of the passages are still remarkably intact. You can apparently still see tool marks carved into the walls, which feels strangely personal considering the tunnels were dug more than four millennia ago.
