SEVERELY ENDANGERED: An eroded section of the Great Wall in north China's Shanxi Province (ZHAN YAN)

As always, the Great Wall, the longest structure built in human history, is seen as a classic symbol of China by the Chinese themselves and others around the world. But just how long is it, exactly?

For a long time, no one could answer that question precisely because of the complexity of the historical project—different parts of the Great Wall were built by different regimes and dynasties over more than 2,000 years and were never quite connected as a seamless whole.

However on June 5, a definitive answer was given by a report released by the State Administration of Cultural Heritage (SACH). It fixed the official length of the Great Wall with all of its branches at a whopping 21,196.18 km, almost 2.4 times the widely believed 8,851.8-km preliminary estimate of 2008.

"The previous estimate referred specifically to Great Walls built in the Ming Dynasty (1368-1644), but this new measure includes the walls built in all dynasties," said Yan Jianmin, an official with the China Great Wall Society, an NGO founded by specialists and scholars to protect the ancient structure.

The latest report was based on an archeological survey that began in 2007, jointly conducted by the SACH and the former State Bureau of Surveying and Mapping. It found that the Great Wall structures span the country's 15 provinces, autonomous regions and municipalities, including Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, Liaoning, Jilin, Heilongjiang, Shandong, Henan, Shaanxi, Gansu, Qinghai, Ningxia and Xinjiang.

A total of 43,721 heritage sites were identified nationwide during the survey, including stretches of the wall, defense works and passes, as well as other related Great Wall facilities and ruins, according to Tong Mingkang, Deputy Director of the SACH.

A great legacy

As the largest human-made structure in the world, the Great Wall is a complex project.

Construction of the Great Wall was initiated by the southern State of Chu in the seventh century B.C. during the Spring and Autumn Period (770-476 B.C.), when China was in a state of anarchy as numerous independently ruled vassal states vied for power. According to Yan, the oldest sections of the Great Wall that have been found are in east China's Shandong Province and central Henan Province. The purpose of the walls was to strengthen defense of local regimes.

In the following years, other states in the north took similar defensive action throughout the Spring and Autumn Period and the Warring States Period (475-221 B.C.). In 221 B.C., Qin Shihuang (259-210 B.C.), the first emperor of the Qin Dynasty (221-206 B.C.), united the whole country and linked those defensive walls built by former northern vassal states together, forming the famous Qin Great Wall, which extended more than 5,000 km from today's Liaoning Province in the northeast to Gansu Province in the northwest.

Today, just a few sections of the Qin Great Wall remain standing in Datong in north China's Shanxi Province and Inner Mongolia Autonomous Region, as well as Minxian County in Gansu.

Construction of the Great Wall continued during the 10 dynasties succeeding the Qin Dynasty. Those walls were built in scattered, but strategic areas to fend off northern nomadic tribes. The two largest-scale constructions took place during the Han (260 B.C.-220) and Ming dynasties. The total length of the Han Great Wall exceeded 10,000 km, and that of the Ming Dynasty was around 6,000 km, according to a research.

Most of the Great Wall still standing today was built more than 600 years ago in the Ming Dynasty. For example, there are 629-km-long Ming Great Walls within the Beijing boundary, including the well-preserved sections in Badaling, Simatai and Mutianyu.

Editor: MetalAllen