A 500-year-old question - Just how long is the Great Wall? - will be answered in 2008 by two Chinese government departments.

A massive geographical survey of the Great Wall will be launched by China's State Administration of Cultural Heritage (SACH) and State Bureau of Surveying and Mapping (SBSM).

The survey will be completed in 2007 and the basic statistics of the Great Wall, including its length and layout, will be released in 2008, officials said.

Local governments have been gathering statistics on the Great Wall since the 1980s. "But due to limited knowledge and technology, much of the Great Wall is still a mystery," said SACH director Shan Qixiang.

"The government needs to organize a scientific survey so we can have a comprehensive and accurate understanding of the Great Wall, " Shan said.

The departments will jointly establish a database based on the results of their survey to facilitate future research and protection of the Great Wall.

Parts of the survey have already started in Hebei and Henan provinces.

The Great Wall was first built in the Warring States Period (475-221 BC), when separate sections were built in various strategic areas to defend China against invasion by northern nomadic tribes.

A large portion of the Great Wall was located in poor, remote areas where few people reside. The traditional estimate of length was 50,000 li, or 25,000 kilometers.

The main remnants of the Great Wall were rebuilt in the Ming (1368-1644) and Qing (1644-1911) dynasties. Together, they were estimated at about 6,700 kilometers.

The wall is generally considered to start at Jiayuguan Pass in Gansu Province and stretch to Shanhaiguan Pass on the shores of Bohai Bay in the east, yet no one knows for sure the ancient wonder's exact length.

Scientists and historians say they will focus their work on the portion of the Great Wall which was built during the Ming Dynasty.

Records show that the Ming portion walls meandered through China's Liaoning, Hebei, Tianjin, Beijing, Shanxi, Shaanxi, Ningxia and Gansu province, autonomous regions and municipalities. The portion was estimated at 5,660 km.

However, experts have warned that only 30 percent of the Ming portion walls are still standing.

Dong Yaohui, deputy president of the China Great Wall Association, said that less than 20 percent of the Ming Great Wall is relatively well protected.

As nature and human activity continue to take their toll on the Great Wall, the Chinese government has increased efforts to protect the unique historical relic.

On Tuesday, the Chinese government issued a regulation to protect the Great Wall. The regulation bans vandalism and driving on the Great Wall, taking soil or bricks and building anything on it that is not designed to protect it.