Actually, not only is china the country in history that built wall along its boundary. For example, The Hadrian's Wall in northern England, built "to separate the Romans from the barbarians", extended 117 kilometers. Even if other countries built amazing walls, the Great Wall of China was unique. The Great Wall was usually built with local materials, mostly earth and stones. After uniting China from seven Warring States, the first emperor of Qin Dynasty connected the walls of the three states in the north and formed the first "Wan Li Chang Cheng". Basically, walls were built at strategic points by different states (Qi, Chu, Wei, Yan, Zhao, Qin, Han) to protect their territories. Armies were stationed along the wall as a first line of defense against the invading nomadic Hsiung Nu tribes north of China (the Huns).If there are an attack, signal fires from the wall provided early warning Building the Great Wall was a tremendous undertaking, just During the Ming Dynasty, it was renovated on 16 occasions to fend of invasions from the northern tribes. Well, but the mystery is how they could build this amazing construction, the fact that about one million people, one fifth of China's population at that time were involved in the project is amazing. The construction result demonstrates the wisdom and tenacity of the Chinese people. Moreover, f or some reason, some urban legends tend to get stated and never disappear. The myth of being able to see the Great Wall from space originated in Richard Halliburton's book Second Book of Marvels. It said that the Great Wall of China was the only man-made object visible from the moon. But as we know the NASA said that it couldn’t be true.