The first Chinese emperor of the Qin dynasty, Qin Shi Huangdi ordered the building of the great wall more than 2000 years ago. The emperor subjugated seven warring states, united them and connected 4 old fortification walls after extending them.
This project of fortification started in 700 BC approximately and served as a strong wall of defense against attacks and invasion from the Huns of northern China. The emperor also stationed armies all throughout the wall.
In the initial phase, the great wall was around 5000 km in length, but underwent a series of renovations through a period of 200 years and now stretches over 4000 miles or 6400 km. Astronauts can view the great wall from the earth’s orbit, so vast is its size.