Part of the ruins of ancient Heisui City of the Xixia Dynasty (1038-1227). The city ruins are now surrounded by drifting dunes near Ejina Banner in west Inner Mongolia Autonomous Region. The city used to be an important part of the Silk Road, but most of its city walls are now buried in sand, and is threatened by encroaching gobi and desert. This picture was taken on May 14, 2006. [Xinhua]