Records about the Great Wall can be tracked back to Qi's Great Wall and Qin's"Qianluo"Great Wall in 408 B.C..Seven powers in the Warring-states Period built the Great Wall except the Han State.In order to defend enemies in the northern frontiers,many later dynasties such as Qin,Western Han,Northern Wei,Northern Qi,Northern Zhou,Sui,and Ming built walls along the borders.The extant Great Wall built by the Ming Dynasty is about 6 700 kilometers.Generally speaking,the Great Wall was built to defend foreign harassment or encroachments,but conditions were not always so,such as the Great Wall built by the Qi State and the Zhao State during the Warring-states Period,the Western Han,the Sui,and the Ming dynasties.To adapt to the need of military defense there was never just one great wall but many branches throughout dynasties.In general,the Great Wall was made of rammed earth and the thickness of the wall was different,and there are also some parts made of stones.
the Great WallQin's Great WallMing's Great Wallmilitary defense
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