"They knew the chances of survival were slim," Zhang says. "But they chose death for their country over life under slavery. This is China's spine, China's spirit."

His passion to honor the heroes bore fruit. Supported by local authorities, a museum was built near the ancient Xifengkou pass, along with a garden with broadsword sculptures, to mark the battle along the Great Wall during the Chinese People's War of Resistance Against Japanese Aggression. Now a national patriotic education base, it houses the 493 relics he has collected over the years.

Liang Yong, a researcher at the Hebei Provincial Institute for Culture and History, says Xifengkou is "a pinnacle of the Great Wall spirit, where Chinese resilience crystallized".

The defense of the Great Wall was a battle waged by the Chinese military and people against the Japanese invaders along the ancient structure. It was an important episode in the early period of the war. After occupying Northeast China, the Japanese military continued its southward push, sending a large number of its Kwantung Army troops to infiltrate areas in North China.