Archaeologists in China’s Inner Mongolia Autonomous Region have unearthed a complex network of underground tunnels dating back approximately 4,300 to 4,500 years. The discovery was made beneath the Houchengzui Stone City, a 1.38-million-square-meter Neolithic settlement situated on the north bank of the Hun River in Qingshuihe County.

The excavation, conducted by the Institute of Archaeology at the Chinese Academy of Social Sciences and regional teams, revealed six intersecting tunnels arranged in a radial pattern. Located between 1.5 and 6 meters underground, the passages typically measure 1 to 2 meters in height and 1.5 meters in width. The structures feature arched ceilings characteristic of Longshan period architecture and retain visible tool marks from their original construction.

Experts state the tunnel system likely served a dual purpose for secret troop movement and emergency evacuation. The Houchengzui site is one of the largest and most heavily fortified early stone cities found in the region, featuring an inner and outer city, fortified gatehouses, and moats. The presence of such a sophisticated defense network indicates a high level of labor organization and strategic planning within the ancient society.

Fieldwork at the site remains active as researchers continue to excavate high-level buildings and burial areas. The archaeological team is currently working to determine if additional hidden passages exist and to further clarify the tunnels' role in the settlement's broader military and administrative infrastructure.