"During the defense at the Great Wall, people across the country donated money and goods, providing strong support to the Chinese army," says Liu Xueqin, a researcher on the history of the Great Wall defense who is now retired.

"The people's selfless support greatly boosted morale among officers and soldiers. They fought bravely and fiercely, dealing heavy blows to the Japanese army and delaying Japan's invasion of North China," Liu adds.

In the 1970s, Xifengkou's landscape transformed as the Panjiakou Reservoir dam flooded 10 km of the Xifengkou pass. This event created today's surreal underwater Great Wall — visible only when the reservoir's water level drops. This project powered the Luanhe River to Tianjin diversion, resolving chronic water shortages in the city.