One of the most recognizable（可辨认的） symbols of China, the Great Wall of China has a long and complicated history.
中国长城历史悠久复杂，是中国最具标示性的象征。
It is not just one wall, but many different walls and fortifications（防御工事） that were built over the course of thousands of years.
这不仅仅是一道墙，它是由不同样式的城墙和防御工事构成，都是人们上千年修建的成果。
The walls built at different times were often built with different materials, everything from packed dirt or wood to stone and brick.
不同时期建造的墙材质都有不同，有泥土、木头还有砖石。
These walls were meant to protect China from invasion（入侵）.
修建这些城墙是为了保护中国不受外来入侵。
The earliest walls were built more than two thousand years ago when individual states built walls of packed earth（紧实的泥土） and gravel（碎石） between boards to protect their territories（领土） from attackers with swords and spears.
最早的城墙修建于两千年前，那时各个地方在边界上用泥土和碎石修建城墙，抵御外部的刀枪进攻，捍卫自己的领土。
Hundreds of years later in 221 BC, the first Emperor（皇帝） of China, Qin Shi Huang, ordered that walls that divided his empire should be destroyed and a new wall connecting the remaining pieces should be built, creating fortifications that protected the empire from northern attackers.
几百年后，中国第一位皇帝，秦始皇，在公元前221年，下令拆除分割了其领土的墙壁，修建与其余地区相连的新墙，设立防御工事，抵御北方入侵者。
No one knows exactly how long that wall was or where it was built, as most of it has worn down or been destroyed.
那座墙具体的长度和位置无人知晓，因其大部分已经坍塌或是被摧毁了。
Over the next thousand years, different ruling（统治） dynasties repaired, rebuilt, or expanded sections of the wall.
在接下来的几千年里，不同执政王朝对其进行了修补，重建以及扩建。
The leaders of the Ming Dynasty, which began in 1368, constructed the most famous version of the Great Wall.
始于1368年的明朝统治者修建了最有名的一版长城。
They began by building watchtowers and garrisons（要塞）, later adding walls of stone and earth.
他们最先修建瞭望塔和驻防区，之后又加修了石头和土筑成的墙壁。
New construction on the wall ended in 1644.
新一轮的城墙建设于1644年完工。
At its height（鼎盛） the Great Wall stretched more than 13,000 miles or about 22,000 kilometers in total length, making it the longest structure ever built by humans.
在其鼎盛时期，长城绵延13000英里，约22000千米，成为人类建造史上最长的建筑。
In some places the walls were 30 feet or 9 meters thick, and 25 feet or 7.5 meters tall, and it was studded（镶嵌） with as many as 25,000 watchtowers.
有些地方的墙壁厚达30英尺即9米，高约25英尺即7.5米，而且长城上遍布约25000个瞭望塔。
You may have heard that the Great Wall is so big that it can be seen from space, but that is only partially（不完全地） true.
你也许听说过，长城大到可以从太空看见它，但这也不全对。
It cannot be seen at all from the moon, but from a much closer orbit （轨道）it could be seen by someone who knew exactly where to look and what it would look like.
从月球上根本看不到它，但是在更近点的轨道上，确切知道长城位置和外观的人可以看到它。
Today the Great Wall of China is a World Heritage site, protected and maintained for all of humanity to enjoy.
如今，中国的长城已成为被保护的世界遗产景观，供人们欣赏。
Only some pieces of the wall are taken care of, however, as it is simply too big and too damaged by time and old battles to repair and take care of it all.
然而，只有一部分墙壁被修缮，因为它规模太大，遭受时间和战争的损毁太严重，以至于很难进行完全修补。
In fact, nearly 1/3 of the wall has completely disappeared, fallen down and even the stones were taken away by local people to use in building.
事实上，有接近1/3的墙已经完全消失，坍塌甚至有些落下的石头被当地居民带走去建造房屋。
Still, the Great Wall is the most popular place for tourists to visit in China, attracting millions of people each year.
然而，对来访中国的游客来说，长城仍旧是最受欢迎的景点，每年都有数百万人来参观游玩。
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