长城（Great Wall），又称万里长城，是中国古代的军事防御工程，是一道高大、坚固而连绵不断的长垣，用以限隔敌骑的行动。长城不是一道单纯孤立的城墙，而是以城墙为主体，同大量的城、障、亭、标相结合的防御体系。
长城并不只是一道单独的城墙，而是由城墙、敌楼、关城、墩堡、营城、卫所、镇城烽火台等多种防御工事所组成的一个完整的防御工程体系。这一防御工程体系，由各级军事指挥系统层层指挥、节节控制。
长城是中国也是世界上修建时间最长、工程量最大的一项古代防御工程，自西周时期开始，延续不断修筑了2000多年，分布于中国北部和中部的广大土地上，总计长度达5万多千米。
Let's go to the Great Wall of Beijing
The Great Wall, also known as the Great Wall, is a military defense project in ancient China. It is a tall, strong and unbroken Wall used to isolate the movement of the enemy. The Great Wall is not a single isolated wall, but a defensive system with the wall as the main body and a large number of cities, barriers, pavilions and landmarks.
The Great Wall is not just a separate city wall, but by the city wall, tower, Guancheng, pier fort, battalion city, guard post, town beacon tower and other fortifications composed of a complete defense engineering system. This defense engineering system is commanded and controlled by military command systems at all levels.
The Great Wall is the longest and largest ancient defense project in China and the world. It has been continuously built for more than 2,000 years since the Western Zhou Dynasty, covering a vast area of northern and central China, with a total length of more than 50,000 kilometers.
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