Construction of the Great Wall began during the Spring and Autumn Period to the Warring States Period (770 BC – 221 BC), Several ducal states built wall fortifications along the precipitous mountain ridges to ward off the plunder of nomadic people and the invasion of each other. In 221 BC, Qin Shi Huang ordered to link the walls up after he united China.
   
   During the following dynasties, the Great Wall was destroyed continuously by natural disasters and human beings. Amongst the remained broken pieces of walls, those constructed in Ming Dynasty are the most well-preserved and splendid ones.
 
   The Great Wall stretches some 6,300 km from Jiayuguan Pass in the west to the Yalujiang River in the east, traversing 11 provinces, municipalities and autonomous regions. It is the most magnificent ancient military defenses work and one of the most remarkable ancient buildings in the world.