Many viewers of the film Tunnel War were captivated by scenes depicting Chinese soldiers defending a village from invading Japanese troops through skillful use of a network of tunnels. In fact， the use of tunnels during war can be traced back centuries in China. The earliest recorded instance was pulled off in a Ming Dynasty （1368-1644） cave in Shuidong Valley in Lingwu City， northwestern China’s Ningxia Hui Autonomous Region， which is also considered the best-preserved and most complete ancient military defense network along the Great Wall.
　　The artificial cave was chiseled in the cliffs along a 3-kilometer valley， with one end in Hongshan Fort， which was built in 1503. The fort， with a circumference of 1，200 meters， has partially collapsed， but the surviving city walls and towers testify to its past magnificence. According to Wang Huimin， a researcher with the Ningxia Archeology Institute， cavalries from nomadic tribes such as the Tartars and Oirats often rode across the Ming Dynasty’s northwestern border to plunder local residents. The cave emerged as part of a scientific， comprehensive defense network， along with the Great Wall and its accompanying fortresses， that effectively thwarted invasions by nomadic tribes through utilizing local landforms such as valleys and earthen mounds.
　　When it was first discovered， the historic cave had already partially collapsed after centuries of weathering， and people only knew of a few holes in the cliffs. For a long time， the cave was used by locals to store grain until local authorities began the first archeological excavation in 2006.
　　After years of cleaning and digging， 2，000 meters of tunnels through the cave are now open to tourists. Estimates put the open section at only a quarter of the cave’s total tunnels.
　　Visiting tourists often gasp when entering the subterranean labyrinth. The intertwining tunnels and caverns enabled troops to effectively hide and ambush the enemy during wartime， and were used as barracks during peace time. The cave is protected by many booby-trapped holes with sharp spikes or horns waiting at the bottom. Typically， a tunnel is two meters high and one meter wide， allowing only a single person to pass at a time. For this reason， with a good position at the end of a corridor， a single soldier could defend against an entire legion of invaders.
　　Along with tunnels， the cave is also equipped with watch holes， ammunition depots， and weapon storage， as well as a variety of living facilities such as bedrooms， kitchens， granaries， and wells. The cave features impressively-designed lighting and ventilation systems. Particularly， smoke from kitchens was vented outside via specially-constructed ducts that didn’t expose the hideout. With enough food stored， troops could survive a long siege because the wells inside supplied endless water. The entrance to the cave is positioned a dozen meters above the valley floor， so it has never been flooded. The well-designed military base not only testifies to the wisdom of ancient Chinese people， but also reminds us of the cruelty of war.


　　During the latest excavation， archeologists found many ancient measuring tools， such as yardsticks， dou， and sheng （ancient measuring tools for grain）. Before this， most discoveries were weapons. The evidence supports theories that the cave was used as a military fort during war and for storing goods when the cross-border market opened.
　　Despite being unimaginatively named“Troops-Stationed Cave” in historical records， the structure is too magnificent for such a bland name. It is truly a massive underground man-made fortress. Indeed， it is a miracle that such a visceral link to military history has been preserved so completely.