将以下文本翻译成英语，并以markdown的形式输出。
原文：中国的长城是一项伟大的工程，被列为世界七大奇迹之一。长城修建的目的是为了保护中国的边界，防止入侵。它是用砖石砌成的，总长超过20,000公里，其建设历时千年。尽管它的一部分现在已经损毁，但长城仍然是中国的象征，吸引着世界各地的游客前来参观。
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The Great Wall of China is a magnificent project, listed as one of the Seven Wonders of the World. The purpose of its construction was to protect China's borders and prevent invasions. It is built with brick and stone, stretching over 20,000 kilometers, with construction spanning a millennium. Although part of it is now in ruins, the Great Wall remains a symbol of China, attracting visitors from all over the world.
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