The first part of the Great Wall was built about 2,000 years ago as a way to keep people from Mongolia from entering China.
Until the 1600s, many more sections were built and rebuilt, until the wall and its branches eventually spread out over 4,000 miles, from Korea in the east to the Gobi Desert in the west.
The main portion is about 1,500 miles (2,415 km) long. It was built entirely by hand of brick, dirt, and stone.
The first section was constructed at the rate of 1 mile (1.6 km) per day, an astonishing rate of accomplishment.
It is the world’s longest artificial structure.