(File Photo, source: xinhua)

The ancient Xi'an City Wall, a landmark-engineering feat in Xi'an, capital of Shaanxi Province, is under threat from the tides of time.

"There are more than 100 cracks in the wall, and the ancient construction is also suffering from subsidence," said Liu Chuzhang, an official from the Xi'an City Wall Protection Committee.

"I saw a crack only a finger wide in the wall last year, but now a fist can be put through it," said Li Jianzhang, a local resident who exercises everyday in the City Wall Park.

Earlier this month, the protection committee conducted an investigation into the ancient construction and submitted a report to the local government, saying the city wall is now threatened by cracks and subsidence, said Liu.

The wall was built in 1374 during the Ming Dynasty (1368-1644). Standing 12 metres high with a width of 13 metres at the top and 16 metres at the bottom, the 13.7-kilometre wall is the only example of such an ancient construction in China to have been so well preserved.

"Although the wall has been preserved, it has become very much worn over the last 600 years. Since 1983, the wall has been renovated three times, but it still faces a number of serious problems," Liu said.

According to experts in ancient relics protection, the wall is threatened by four major factors: packed earth, holes and cracks, rainwater infiltration and the massive pressure caused by its own weight on the ground.

"The city wall was built on the foundations of the city wall built in the Tang Dynasty (AD 618-907) and the packed earth inside the older wall is different from that used in the Ming Dynasty. It cannot bear the heavy tread of so many tourists the ancient city wall is one of the hottest tourist spots in Xi'an," said Wang Yingliang, an expert in ancient building protection.

Wang said the wall used to have a good drainage system, but now many of the drainage facilities are damaged, creating pools of water on the wall and rain infiltration. Moreover, the holes made in the wall during war time have made the situation all the more serious.

"The increase of pressure on the ground as a result of high-rises built in recent years around the wall and the excessive extraction of ground water have led to subsidence and cracks," the expert said.

"Recreational and commercial activities staged on the wall should be limited or forbidden, in order to better protect the ancient construction," said Liu Qi, a member of the Xi'an Committee of the Chinese People's Political Consultative Conference.

Editor: Wing