Cheng constantly observes and learns the details of the ancient construction, and enriches his historical knowledge in the hope of passing on to his predecessors.[Photo by Ma Wenxiao/For China Daily]

For him, even if hundreds of years have passed, the materials, craftsmanship and methods used in ancient buildings still need to be strictly observed. "As a cultural relics protection worker, it is our responsibility to eliminate the use of materials that are not made according to traditional requirements. We have the responsibility to pass on the cultural relics protection methods and cultural protection spirit from generation to generation," he says.

In 2018, the traditional restoration technology of the Ming Dynasty (1368-1644) Great Wall was included in the sixth edition of the district-level intangible cultural representative heritage list of Huairou.

The inheritance of this technology is currently his most urgent concern as most of the repairers are old, and young people are reluctant to work as bricklayers.

"To make the traditional restoration technology of the Great Wall widely spread, applied, summarized and improved, we need to attract more people to engage in this work, and foster the training culture of relics protection," he says.