Emperor Qin Shi Huang (221 to 210 B.C.) gets credit for beginning construction of the Great Wall. Historical records as old as the fifth century B.C. mention fortifications that may have been precursors to the Great Wall.
The Great Wall runs across northern China. It extends from the Heilongjiang province, east of Beijing near Korea, to China's westernmost province of Xinjiang.
Building continued over hundreds of years. The last and largest construction period occurred during the Ming Dynasty (A.D. 1368 to 1644). The Ming rulers repaired older sections and expanded the wall's reach.
Chinese rulers built the Great Wall to keep out invaders entering from the north on horseback, including the Mongols. They also wanted to prevent dissident Chinese from leaving China to cooperate with potential invaders.
Most visitors today tour the Badaling section of the Great Wall, built during the Ming Dynasty and located about 43 miles from Beijing. The section is built of granite and brick and is wide enough for five or six horses to stand side-by-side.
Contrary to legend, the Great Wall isn't visible to the unaided eye from space, according to NASA. This is due to the fact that the wall is made from materials that are similar in color and texture to the surrounding landscape.
