Archaeologists also discovered a secret door under the Great Wall.

"We speculate that Ming Dynasty scouts could conduct reconnaissance through this secret pass under the Great Wall to observe the enemy's situation," Shang says.

During the on-site investigation, experts in ancient architecture, construction materials and botany were involved.

"In the past, when damage was found on the Great Wall, the authorities immediately sent workers to repair it, during which 'involuntary damage' was also likely to occur," Shang says.

He adds that with experts sharing the information from all disciplines, in the future, repairs can be worked on while researchers carry out digital restoration.

The Great Wall has been plagued with "illnesses" such as water erosion. The multidisciplinary team has come up with a plan to overcome such problems.

"When it rains, gravel and sediment block the drainage outlet of the defense structure, which is likely to cause parts of the wall to collapse. Therefore, such blockages need to be dredged in time. The experts have measured and designed a drainage channel to help prevent the risks," Shang says.

The Great Wall is a UNESCO World Heritage Site, consisting of many interconnected walls. Beijing has planned to comprehensively protect and develop a Great Wall cultural belt, with a total area of about 5,000 square kilometers, which includes both heritage protection and ecological conservation.

Xinhua