Great Wall of China length announced after five-year study

The Great Wall of China has a new official length, according to a report by the state-run Xinhua news agency.

A Chinese government survey found that the wall measures 13,170.6956 miles, or 21,196.18 km, the Xinhua report said. 

This means the Great Wall is much longer than previously thought. A preliminary study released in 2009 put the length of the wall at 5,500 miles, or 8,850 km.

The survey began in 2007, and results were released Tuesday in Beijing by the State Administration of Cultural Heritage.

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Deputy chief Tong Mingkang said a total of 43,721 heritage sites were identified during the survey, "including stretches of the wall, defense works and passes, as well as other related Great Wall facilities and ruins."

The Great Wall of China is the world's largest human-made structure. It was built over numerous dynasties to protect the northern Chinese border from invaders, with the majority of the existing wall constructed during the Ming Dynasty.

The Great Wall was put on UNESCO's list of World Heritage sites in 1987.

But the wall has been heavily damaged from human activities, including mining, infrastructure development and tourism. 

Only 8.2 percent of the wall built during the Ming Dynasty remains intact, and 74.1 percent of the wall is in poor condition. A significant amount of the wall has collapsed, the Xinhua report said. 

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