The wall of china was built by the First Emperor of China Qin Shi Haung, when he connected the already fortifications built-in Spring and Autumn (771-476 BC) and during the warring periods  (475-221 BC). The purpose of connecting these fortifications is to protect the Chinese Boundaries from the Asian Nomads. The walls of this great wall of China are built of rammed earth using forced labor. By 212 BC, the boundaries of this wall expanded from Gansu to Southern Manchuria. 
The later Emperors including Han and Ming worked towards the rebuilding and modification of the wall. The Han built the wall to the west while the Qi contributed to extending 16,00 kilometers in the world. Though the wall was built to prevent invasions from enemies throughout history the Wall failed to protect the boundary people and is merely scenery right now. 

中國長城的歷史

中國的城牆是由中國第一任皇帝秦始皇（秦始皇）建造的，當時他連接了在春秋兩季（771-476 BC）和交戰時期（475-221 BC）建造的防禦工事。連接這些防禦工事的目的是保護中國邊界不受亞洲游牧民族的侵害。中國這堵長城的城牆是用強迫勞動夯實的泥土建造的。到公元前212年，這堵牆的邊界從甘肅擴展到了滿洲南部。
包括漢和明在內的後來皇帝都致力於重建和改建隔離牆。漢族在西邊築牆，而齊族則向世界延伸了16公里。儘管隔離牆是為防止敵人入侵而建造的，但在整個歷史上，隔離牆都未能保護邊防人員，只是現在的一處風景。

https://en.wikipedia.org/wiki/History_of_the_Great_Wall_of_China