The Great Wall of China is even greater than previously thought, according to the first detailed survey to establish the length of the ancient barricade.

一份详细的测量古防御工事长度的调查称，中国万里长城比我们现在想象的要更伟大。

The structure is a series of walls first linked up more than 2,000 years ago

A two-year government mapping study found that the wall spans（持续，贯穿） 8,850km (5,500 miles) - until now, the length was commonly put at about 5,000km.

Previous estimates of its length were mainly based on historical records.

Infra-red（红外线的） and GPS technologies helped locate some areas concealed（隐藏的） over time by sandstorms, state media said.

The project found that there were wall sections of 6,259km, 359km of trenches（沟渠）, and 2,232km of natural defensive barriers such as hills and rivers.

The study was carried out by the State Administration of Cultural Heritage（文化遗产） and the State Bureau of Surveying and Mapping.

Barricade

Experts said the newly-discovered sections of the wall were built during the Ming Dynasty (1368-1644), and stretch from Hu Mountain in northern Liaoning province to Jiayu Pass in western Gansu province.

The project will continue for another 18 months in order to map sections of the wall built during the Qin (221-206BC) and Han (206BC-9AD) Dynasties, the report said.

The wall, the world's largest man-made structure, was built to protect the northern border of the Chinese Empire.

Archaeologists（考古学家） had lobbied for the survey to be done to provide scholars with an accurate understanding of the construction.

Known to the Chinese as the "long Wall of 10,000 Li", the Great Wall is in fact a series of walls and earthen works begun in the 5th Century BC and first linked up under Qin Shi Huang in about 220BC.

It was listed as a Unesco（联合国教育科学文化组织） world heritage site in 1987.