An area in northern Shanxi Province imaged on 9 January 2001. The low sun angle and light snow cover highlight a section of the Great Wall, visible as a black line snaking diagonally through the image from lower left to upper right. The Great Wall (actually a series of walls) is over 2,000 years old and was built over a period of 1,000 years. Stretching 8,850 km (5,500 mi) from Korea to the Gobi Desert, it was built to protect China from northern marauders. Click on photo for higher resolution. Image courtesy of NASA.