Why was the Great Wall of China built?

The Great Wall of China was built as a military defensive line to defend the invasions from some northern nomadic nations. Apart from the function of defense, the wall also boosted the economy, as well as promoted the culture exchange and national integration of different nations at its two sides. 

 

Why did they build the Great Wall of China? The Great Wall was not only a simple wall, but also a comprehensive military defensive system which connected the beacon towers, fortresses and strategic passes together. It blocked nomadic nations and protected Han people and their territory from invasions in several ways:
 

In ancient times, the soldiers were arranged to garrison at the beacon towers to look at the enemy's position in the distance and delivering the battle signals to other soldiers in next beacon tower once the enemies getting closer, so the army was always ready for the battle.

In 1991, there was an experiment taken along the Great Wall. There were two groups of people required to deliver the message on the wall by beacon towers and cars respectively. The experimental distance was 11.27 kilometers (about 7 miles). The message sent to the destination by beacon towers only used 7 minutes 26 seconds, while the car took 9 minutes 5 seconds. It was not hard to see that the beacon towers on the wall really played an important role in the battles from this experiment.
 During the battles, the daily supplies including the foods, weapons and horses supported the basic needs of soldiers. The border of the country was quite long and the battle terrain could be very steep, so it could not guarantee that the supplies would be sent to the battlefield in time. However, the Great Wall made this happen, which helped the soldiers to convey the suppliers more easily and conveniently along it. Nevertheless, the enemies didn’t have such advantages.
 

There were lots of soldiers stationed in each fortress. Once one fortress was attacked, the reinforcement could be sent there from nearby fortresses and strategic passes quickly along the wall. In this case, this defense line was further strengthened to protect the people and territory.

 See more Did the Great Wall of China Work?
 

 

In ancient time, the south of the Great Wall, the Central Plain mainly maintained the progressive agricultural economy, while the north of the Great Wall, nomadic nation primarily developed the animal husbandry economy. In peace time, these two kinds of economy exchanged the daily goods with each other along the Great Wall. The people in the Central Plain sold grain and cloth to the nomadic tribes, while the nomadic tribes exported the horses and animal products like leather and string to the Central Plain along the walls.  Furthermore, it gave the chance to have the cultural exchanges and promote national integration. One example was that when the Tujue army was defeated in the Tang Dynasty (618 - 907), the emperor ordered those capitulated soldiers lived along the Great Wall and appointed some soldiers as the general. Gradually, they admitted and accepted the advanced culture of Han nation.

 

In the Han Dynasty (202 BC - 220 AD), the emperor ordered an emissary to visit Western Regions, which developed the Silk Road. In addition, the emperor also commanded to build the Great Wall along Hexi Corridor, a section of the Silk Road. This action protected the safety of the Silk Road, which promoted the culture, politics and economy exchange between China and other countries as well.

 See more about the Relation Between Great Wall & Silk Road
 

In the history of Great Wall construction, every state and dynasty built the walls as the defensive line to protect their people and territory from other states or northern nomadic tribes.
 

State/Dynasty	Defend Against
Qi State	Chu State
Chu State	Qi, Qin States
Yan State	Qi, Zhao, Qin States
Zhao State	Donghu, Wei States
Wei State	Qin State
Qin Dynasty	Huns, Rouzhi, Qiang
Han Dynasty	Huns
Northern Wei Dynasty	Rouran
Northern Qi Dynasty	Tujue, Khitan
Sui Dynasty	Tujue
Jin Dynasty	Mongols, Tangut
Ming Dynasty	Tatar, Oirat, Jurchen