Miles out: The Great Wall of China is 13,170 miles long... that's more than twice the length of previous estimates

The Great Wall of China is a lot greater than anyone thought.

The first formal measurement of the world's largest man-made structure revealed the wall was more than twice as long as previous estimates.

In an archaeological survey that took five years to complete, China's State Administration of Cultural Heritage announced yesterday that the wall measures 21,196.18 km (13,170.69 miles).

The Great Wall of China north of Beijing, China. The Great Wall of China is among Seven Wonders of the World

That's considerably longer than the previous mark of 8,850 km (5,500 miles), which was based largely on historical records.

The Great Wall was started in 500 BC and first linked up under leader Qin Shi Huang in about 220 BC to protect China's northern border and fend off foreign invaders. It grew to link up 15 provinces and was reinforced and extended many times during later dynasties.

The previous estimate in 2008 only included structures built during the Ming Dynasty, which lasted from 1368 to 1644, and didn't count some of the ruins.

Only 8.2 per cent of the wall built during the Ming Dynasty remains intact, 74.1 per cent is in poor condition, and in some sections, only its foundation remains, according to the report. A large amount of the wall has collapsed.

The wall was put on the United Nations Educational, Scientific and Cultural Organisation's list of World Heritage sites in 1987.



The survey revealed a total of 43,721 heritage sites.

Longer: A backpacker walking along section of wall at Jinshanling, near Beijing

But Chinese officials warned in the report that the wall is threatened by natural forces as well as human development along its borders.

Damage from mining, tourism and infrastructure development have taken their toll in recent years, said the survey.

'The saving and preserving of the Great Wall's relics should not be delayed,' the report stresses.