Large-scale construction of the Great Wall was ongoing throughout the reign of Emperor Wu Di in the Han Dynasty (206 BC一220 AD). With the experience drawn from the wars with the Huns, the emperor found out that the Great Wall was an effective means of defense against harassment from the Huns. Apart from maintaining and utilizing the Qin Great Wall, they built an Outer Great Wall, about 500 kilometers to the north of the Qin Great Wall, in order to ward off the Huns as well as to protect the Silk Road. They also had the Great Wall extended towards the west for another 5, 000 kilometers long to the Lop Nur Lake in today’s Xinjiang Uygur Autonomous Region.
The Han Great Wall started from the Liaodong Peninsula in the east, and ended at the foot of the Tianshan Mountain in Xinjiang Uygur Autonomous Region, with a total length total length of 10,000 kilometers (6,200 miles). But the Han Great Wall was not that high and wide it could only be used to block the view of the enemy, thereby taking them feel puzzled and preventing the enemy’s cavalries from making a sudden attack.
During the Tang Dynasty (618- 907AD), the Tang Empire entered its flourishing period. They expanded the frontier further to the north. So the Great Wall lost its function for almost 300 years.