The Great Wall of China, or the Chinese Wall, is one of the major architectural achievements of the premodern world. Around the seventh century B.C.E.,the state of Chou in North China started to construct a permanent frontier-defense system, and by the third century B.C.E. various other northern kingdoms had followed suit. Although subsequent dynasties, such as the Han (206 B.C.E. -220 C.E.) and the Sui (589- 618), improved various sections of wall, it was not until the Ming empire (1368-1644) that many fragments were connected into one continuous wall. The emperor Hongzhi (reigned 1487-1505) ordered most of the work on the existing Great Wall in order to repel another Mongolian invasion.

The Ming Great Wall is approximately 4,500 miles long, extending from the mountains of Korea to the Gobi Desert (the distance between Miami, Florida, and...