Around 8th century BC:

During the Western Zhou Dynasty, minority groups living in Northwest China frequently invaded the border. The 11th king of Western Zhou Dynasty assigned his subjects to build watch towers and fortresses in northwest Inner Mongolia and to the north of the Yellow River.

770-221 BC:

The kingdoms of Qi, Chu, Wei, Yan, Zhao, Zhongshan and Qin, the powers of the Spring and Autumn Period and the Warring States Period, built walls and extensive fortresses to defend their borders against each other. Most of the walls were built from dykes connecting mountains, which were initially used to prevent floods.

215-209 BC:

The first emperor of the Qin Dynasty, Qin Shi Huang, conquered all opposing kingdoms and unified China. To prevent the resurgence of feudal lords, the emperor had walls between the former states destroyed. A new wall to connect the remaining fortifications along the empire's new northern frontier was built to defend against intrusions from the north.

130-102 BC

During the Han Dynasty, the Great Wall underwent a large-scale repair and extension to Jiuquan in Gansu province to defend against invaders from the north. The wall was extended east to Korea and west to Xinjiang.

AD 423-608

The Northern Dynasty and Sui Dynasty witnessed continual repair, rebuilding and expansion of the Great Wall.

1058-1199

During the Jin Dynasty, emperors constructed defensive walls located north of the Great Wall as we know it today, reaching Inner and Outer Mongolia, and even Russia. Most have double walls and trenches.

1368-1568

The Ming Dynasty devoted huge resources to extending, rebuilding and reinforcing the walls, making them more elaborate and stronger. The Great Wall was then extended west to Jiayuguan in Gansu province and east to Hushan in Liaoning province. The wall we see today is primarily the remnants of the Ming constructions.

1923

Article in National Geographic magazine begins: "According to astronomers, the only work of man's hands which would be visible to the human eye from the moon is the Great Wall of China." US, Russian and Chinese astronauts later say it's wishful thinking.

2006

Chinese government passed the first national law to protect the Great Wall. Ming artifacts cannot be bought or sold.

Compiled by Irene Deng

(China Daily 01/08/2012 page1)