Heicheng, the largest and best preserved ancient city site along the Silk Road that linked China with Central and Western Asia, is jeopardized by flowing sand and protected at the national level as a major historical and cultural site. (Photos: Xinhua)

About 25 km to the southeast of Dalai Hubu Township in north China's Inner Mongolia, the archeological site is well known for its ten-meter-high city walls and a pagoda dating back to the Xixia Dynasty (1038-1227).

Photo taken on Oct. 18, 2019 shows a view of Heicheng relic site in Ejina Banner, north China's Inner Mongolia Autonomous Region.

Photo taken on Oct. 18, 2019 shows a view of Heicheng relic site in Ejina Banner, north China's Inner Mongolia Autonomous Region.

Photo taken on Oct. 18, 2019 shows a view of Heicheng relic site in Ejina Banner, north China's Inner Mongolia Autonomous Region.

Aerial photo taken on Oct. 19, 2019 shows scenery of Heicheng relic site in Ejina Banner, north China's Inner Mongolia Autonomous Region.

Photo taken on Oct. 18, 2019 shows a view of Heicheng relic site in Ejina Banner, north China's Inner Mongolia Autonomous Region.

A tourist visits Heicheng relic site in Ejina Banner, north China's Inner Mongolia Autonomous Region, Oct. 18, 2019.