In the third century B.C., the first emperor of a united China, Shih Huang Ti of the Ch’in dynasty, conceived a plan to defend against invasions by nomadic tribes to the north. The plan was to create a single defensive wall by connecting the various walls erected by formerly independent kingdoms. The result was the Great Wall of China, the longest defensive structure ever built.

Although the wall often failed to keep invaders out, it nonetheless proved to be a valuable defense system. First, it contained a network of watchtowers, several stories in height, that transmitted word of enemy movements by smoke or fire signals. Second, the top of the wall was as much as 35 feet wide and acted as a highway that facilitated the transport of troops and equipment in response to those signals.

Following extensions made in other periods, particularly by the Ming dynasty in the late 1400s, the Great Wall now stretches for approximately 4,000 miles, winding like a dragon over mountains and along desert borders. Much of the Great Wall was destroyed when, beginning in the 1960s, China’s communist government led a 20-year attack against the nation’s cultural traditions. In 1984, Deng Xiaoping began a new campaign to “love our country and restore our Great Wall.” It now stands as an unofficial national symbol.

PostScript: The Great Wall was built by forced laborers, using only their hands. Legend has it that the bodies of deceased workers were among the building materials used to erect the structure. Accordingly, the wall has been called the longest cemetery in the world.