It was not until the Qin Dynasty that the separate walls, constructed by the states of Qin, Yan and Zhao kingdoms, were connected to form a defensive system on the northern border of the country by Emperor Qin Shi Huang (also called Qin Shi Huangdi by westerners or the First Emperor). After the emperor unified the country in 214 BC, he ordered the construction of the wall. It took about ten years to finish and the wall stretched from Lintao (in the eastern part of today's Gansu Province) in the west to Liaodong (in today's Jilin Province) in the east. The wall not only served as a defence in the north but also symbolized the power of the emperor.From the Qin Dynasty onwards, Xiongnu, an ancient tribe that lived in North China, frequently harassed the northern border of the country.

During the Han Dynasty, Emperor Wu (Han Wu Di), sent three expeditions to fight against the Xiongnu in 127 BC, 121 BC and 119 BC. The Xiongnu were driven into the far north of the Gobi. To maintain the safety of the Hexi Corridor (today's Gansu Province), the emperor ordered the extension of the Great Wall westward into the Hexi Corridor and Xinjiang region. The ruins of the beacon towers and debris of the Han Wall are still discernible in Dunhuang, Yumen and Yangguan. A recent report shows that ruins of the Han Wall have been discovered near Lopnur in China's Xinjiang region. Further construction and extensions were made in the successive Northern Wei, Northern Qi and Sui dynasties.The present Great Wall in Beijing is mainly remains from the Ming Dynasty (1368 - 1644). During this period, bricks and granite were used when the workers laid the foundation of the wall and sophisticated designs and passes were built in the places of strategic importance. To strengthen the military control of the northern frontiers, the Ming authorities divided the Great Wall into nine zones and placed each under the control of a Zhen (garrison headquarters). The Ming Wall starts from Yalujiang River (in today's Heilongjiang Province), via today's Liaoning, Hebei, Inner Mongolia, Shanxi, Shaanxi, Ningxia provinces, to Gansu. The total length reaches 12,700 li (over 5,000 kilometers). The Shanhaiguan Pass and the Jiayuguan Pass are two well-preserved passes at either end.

Today, the Wall has become a must-see for every visitor to China. Few can help saying 'Wow!' when they stand on top of a beacon tower and look at this giant dragon. For centuries, the wall served succeeding dynasties as an efficient military defence. However, it was only when a dynasty had weakened from within that invaders from the north were able to advance and conquer. Both the Mongols (Yuan Dynasty, 1271-1368) and the Manchurians (Qing Dynasty, 1644-1911) were able to take power because of weakness of the government and poverty of the people but never due to any possibility of weakness of the Wall.