The Great "Great wall"

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. Overall, the wall extends about 1500 miles (2400 kilometers).

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.