The China's nationwide drive to green the barren western region has resulted in an unexpected substantial reward: the discovery of a unique ancient city covered by desert sands for above 1,000 years.

It is the only ruined city of the Xiongnu (Huns) ever found, said Dai Yingxin, a well-known Chinese archaeologist. The Xiongnu was a northern nomadic ethnic group that was influential in northern China for 10 centuries in ancient times.

The uncovered city occupies one square km in Jingbian County in northwest China's Shaanxi Province, adjacent to the Inner Mongolia Autonomous Region.

It was built by more than 100,000 Xiongnu people in the year 419. Named "Tongwancheng", which means "unify all countries", the city is composed of three parts, the palace walls, the inner city and the outer city. Watchtowers stand at the four corners of the complex.

The 16-30 meter thick city walls are made with sand and white-powdered earth mixed with glutinous rice water. This mixture made the earthen walls as hard as the stone walls.

From a distance, the white city looks like a giant ship. The southwestern turret, the highest of the four, is 31 meters high and looks like a ship's mast. The ruined city is now fenced with brush-wood, trees and grass.

"It is the most substantial, magnificent and well-preserved city to be built by any ethnic group in the history of China," said Zhu Shiguang, president of the China Ancient City Society.

The Turkish-speaking Xiongnu tribesmen founded their first steppe empire in the 3rd century B.C. By the time the Qin Dynasty conquered the other six states and began its reign over a unified China in 221 B.C., the nomadic ethnic Xiongnu had grown into a powerful invading force in the north and started expanding both east and west.

The Xiongnu threat was a constant problem for the Han rulers. Qin Shihuang, the first emperor of the Qin Dynasty, sent a 300,000-strong army headed by General Meng Tian to drive the Xiongnu northward for 350 km and built the Great Wall to guard against its invasion.

Tongwancheng(统万城Tŏngwànchéng) used to be a prosperous city on the upper reaches of the Wuding River, a major tributary of the Yellow River. It remained the political, economic and military center of the southern part of the Ordos Plateau for over five centuries. As a result of the drying up of the river, it then gradually became buried by moving sand and totally disappeared into the desert for more than 1,000 years, said Xing Fulai, a research fellow at the Shaanxi Provincial Institute of Archaeology(Archäologie).

The discovery of the city gives vital information to the study of Xiongnu tribesmen, who have remained a mystery to Chinese and foreign archaeologists because of a lack of adequate material and evidence on this ethnic tribe. Because of their cultural significance, the ruins of this ancient city will be considered for the world heritage status by UNESCO(United Nations Educational, Scientific, and Cultural Organization: an agency of the United Nations that promotes education and communication and the arts).