View from the watching tower at the Overhanging Great Wall in Jiayuguan. The foreground is the Black Hill where the Overhanging Great Wall section is built. The Qilian Mountains with snow capped peaks can be seen at a distance in the background. In the middle is the narrow stripe of flat fertile land known as the Hexi Corridor at its narrowest point, about 8 kilometers (5 miles). The Jiauyguan Great Wall fortress can be barely seen in the upper left side of this picture. Historically, this is an important military defense point for China.