China: 4300-year-old secret ‘tactical defence’ tunnels unearthed

Archaeologists have unearthed a sophisticated triple-defence system and an intricate network of tunnels at the ancient Houchengzui Stone City in Inner Mongolia, China. This archaeological marvel, believed to be around 4,300 to 4,500 years old.

Spread across half a square mile, it stands as the largest and most heavily fortified archaeological site in Inner Mongolia from the early Longshan period (3000 to 1900 BC).
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The ongoing excavation, which was initiated in 2005, has revealed the complex triple-defence system comprising the main city wall, terraces, gatehouse walls, moats, and trenches. The recent undertaking by the Institute of Archaeology, Chinese Academy of Social Sciences (CASS), has brought to light a new layer of defence – an elaborate tunnel system beneath the city.
Believed to serve dual purposes, these ancient tunnels must have been used both as a transportation network and a means of defence and offence. Featuring arched ceilings reminiscent of Longshan period cave dwellings, the tunnels, measuring 3-6 ft in height and approximately 4 ft in width, spread out in a radial pattern, connecting to the centre of the subterranean city.

Several tunnels pass under the fortified city walls, extending beyond its boundaries. Sun Jinsong,

Director of the Cultural Relics and Archaeology Academy of Inner Mongolia, explained that some passages open from outside the city, and pass through various structures like the outer Wengcheng city wall, trenches, and the Wengcheng square.

The strategic design of Houchengzui Stone City, with its elaborate defence systems and concealed tunnels, elaborates its cultural significance in military defence, reflecting its role as a strategic location.

The stone city comprises an inner and outer city fortified with three concentric walls, guarded gates, and trenches. The recent excavations, conducted from 2019 to 2023, focused on the Wangcheng gate, high-level buildings in the inner city, and the tomb area.

Researchers have categorised the city's architecture into simple and complex stone masonry and earthen walls. Simple stone city walls, positioned along ridges, are constructed with layers of stones and filled with loess or earth. Over the five-year excavation, the team uncovered various elements, including city walls, gates, horse faces, trenches, platform foundations, underground passages, house sites, and tombs.
Among the notable discoveries are the main city gate (CM1), urn city gate (CM2), and outer urn city gate (CM3). Descriptions of the main city gate highlight its rectangular plan, measuring about 15 m in length from north to south and 9 to 11 m in width from east to west, with intricate features, such as doorways, gate walls, earth platforms, and other architectural elements.

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The ongoing exploration of Houchengzui Stone City continues to provide valuable insights into ancient civilization, military strategy, and architectural prowess during the Longshan period.