The Great Wall of China is not a continuous wall but is a collection of short walls that often follow the crest of hills on the southern edge of the Mongolian plain. The Great Wall of China, known as "long Wall of 10,000 Li" in China, extends about 8,850 kilometers (5,500 miles).
A first set of walls, designed to keep Mongol nomads out of China, were built of earth and stones in wood frames during the Qin Dynasty (221-206 BCE).
Some additions and modifications were made to these simple walls over the next millennium but the major construction of the "modern" walls began in the Ming Dynasty (1388-1644 CE).
The Ming fortifications were established in new areas from the Qin walls. They were up to 25 feet (7.6 meters) high, 15 to 30 feet (4.6 to 9.1 meters) wide at the base, and from 9 to 12 feet (2.7 to 3.7 meters) wide at the top (wide enough for marching troops or wagons). At regular intervals, guard stations and watch towers were established.
Since the Great Wall was discontinuous, Mongol invaders had no trouble breaching the wall by going around it, so the wall proved unsuccessful and was eventually abandoned. Additionally, a policy of mollification during the subsequent Ch'ing Dynasty that sought to pacify the Mongol leaders through religious conversion also helped to limit the need for the wall.
Through Western contact with China from the 17th through 20th centuries, the legend of the Great Wall of China grew along with tourism to the wall. Restoration and rebuilding took place in the 20th century and in 1987 the Great Wall of China was made a World Heritage Site. Today, a portion of the Great Wall of China about 50 miles (80 km) from Beijing receives thousands of tourists each day.