About a fifth of the Great Wall built in the Ming Dynasty (1368-1644) has disappeared in north China's Inner Mongolia Autonomous Region, an archaeologist said on Tuesday.

The vanished parts were 157.515 km long, said Tala, head of the Inner Mongolia Autonomous Regional Institute of Cultural and Historical Relics and Archaeology.

The statistics were based on newly-released survey results from the Inner Mongolia Autonomous Regional Surveying and Mapping Bureau and the Inner Mongolia Autonomous Regional Institute of Aerial Remote Sensing, Surveying and Mapping, he said.

In recent centuries, the Great Wall has been damaged by weather and human activities, leading to the disappearance of some sections, he said.

The Great Wall, unique in size and style in the world, was China's line of defense during much of its long history. Different sections meander across thousands of miles, passing through many provinces and autonomous regions, including Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Hebei and Liaoning in north China.

Its construction began during the Warring States Period (475-221 BC), when sections were built in scattered strategic areas. The most visually striking part is generally considered to be a well-preserved 6,350 km section from the Ming Dynasty.

The Wall was listed as a United Nations World Heritage Site in 1987.

Inner Mongolia has 15,000 km of Great Wall sections built in different dynasties, accounting for one third of the country's total.

Authorities in the region launched a preservation project earlier this year to protect the Wall's original architecture, including some reinforcement work.

It is expected to last for two to three years with a planned cost of 100 million yuan (14.7 million U.S. dollars), according to the Inner Mongolia Autonomous Regional Culture Department.

(Xinhua News Agency December 31, 2008)