At first people in the village did not understand their motive and referred to them as "lunatics", as they ran up the mountains and roamed along the Great Wall "for nothing". But the four used to smile back and just tell the villagers to take good care of the Great Wall, because "it is the root of Beiloukou's culture and history".

As time went by, their efforts began yielding results. The farmers gradually realized that if they continued to "steal" bricks and rammed earth from the Great Wall, it would eventually disappear one day. More important, thanks to their efforts, the village farmers started talking with them to know more about the history of their village and its connection with the Great Wall.

Nie said: "Our energy is limited, but people's power is limitless. Our purpose is to make the whole village as obsessed about history as we are. We want our children and grandchildren to understand the history of this village and pass it on to future generations."

Chang likes watching historical documentaries on TV and reading history books. He said that he has to recharge his batteries with knowledge, stressing that history is like a book that no one can finish reading as "the more one knows, the more he will realize he doesn't know anything".

Apart from water, simple food, mainly steamed buns, a compass, a pair of binoculars and torches, they also take their medicines with them, because all of them have underlying medical conditions. The medicines include isosorbide dinitrate-like pills which are used to treat heart failure due to systolic dysfunction, esophagus spasms, as well as to treat and prevent chest pain because of lack of flow of blood to the heart.

Once Nie fainted due to low blood pressure during patrol with the other three deep in the mountains. When he regained consciousness after a long time, he said, "I felt reassured … seeing the three old men beside me at the foot of the Great Wall." He added: "But I was also scared as I passed out, because I still had too much work left to finish my 'research' on the Great Wall."

Nie did not tell his wife about the incident, because he fears that after hearing it, she will not allow him to patrol the Great Wall again.

Li and Liu attach great importance to persuading the farmers to protect the old buildings in the village. They complained about the lack of historical records about the buildings. "It's a pity the village has few records of its own long history," Li said.

Still, thanks to their efforts, the village was recognized as a national-level ancient village in 2018. Which means more government funds will be made available for the protection and upkeep of the village's buildings and local intangible cultural heritages.

And due to the inflow of tourists, more and more villagers have come to value the history and culture of the village and the importance of the Great Wall.

Zhi Man'gang, a civil servant of the county's cultural relics bureau, said that the four men have made great contributions to the protection of the Great Wall in and around Beiloukou and the development of the village. "Within a decade, they have changed all the villagers' attitude toward the Great Wall and their own history."

"It is because of the unflinching efforts of these mostly unknown people that the Great Wall and other cultural relics in the county have been preserved for thousands of years," Zhi added. "They are the unsung heroes."