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Sandstorms in northern China are reducing large sections of the Great Wall to rubble.
Archaeologists say chunks of one of the seven wonders of the world could be gone in 20 years, swallowed up by the Badain Jaran desert.
More than 20 centuries old, the Great Wall once
stretched 6405km through China, from Shanhaiguan Pass in the northeastern province of Hebei to Jiayuguan Pass in the north-western province of Gansu. The wall was built to defend China against invasion by northern nomadic tribes.
About 500km from the Jiayuguan Pass lies Minqin county, where 60km of the wall is disappearing rapidly, a victim of extensive farming since the 1950s, which has sapped underground water and destroyed the local ecology.
"This section of Great Wall was made of mud rather than brick and stone, so is more prone to erosion," Zhou Shengrui, a former curator of the local museum, told the Xinhua news agency.
"Similar erosion happened in other places, but the situation is worse here. Frequent storms not only eroded the mud, but also cracked the Wall and caused it to collapse or break down."
This historic section of the great defensive structure was built during the Han Dynasty which lasted from 206BC to AD220, and extended during the Ming Dynasty (1368-1644).
More than 40km of wall in Minqin have disappeared in the past 20 years. The wall is just 2m tall in places where once it stood 5m high.
Since the 1960s, the area has become ever more parched. The Qingtu Lake has dried up in the past 30 years and been swallowed by the Badain Jaran, the world's fourth largest desert.
Local residents talk of how the Great Wall gets shorter every year. "When I was 7 or 8 years old, the section of Great Wall west of my village was still as new. We used to walk on it like the ancient soldiers," Wei Zhaobai, 61, a resident of Chengxi village in Minqin, told Xinhua.
In a bid to fend off the encroaching desert, local workers were covering the wall remains with more sand and dirt.
"If sandstorms strike again, it will take some time to blow the top-dirt away, and that'll give us time to build barriers and plant trees," said Zhou.
The Great Wall gets an estimated 10 million visitors a year. These days, China's national symbol is in a sorry state, with only about 2500km of it left standing.
"It saddens me to see the Great Wall being blown away, but we hope it can be a warning of what we have done to ourselves and our environment," Zhou said.
- Independent