Guo Wei
Guo Wei， writing & living in China
Answered Jul 14， 2016
The Great Wall served as a highway only for the military. Soldiers could mobilise on it and go wherever urgencies emerged. As for civilians， they weren’t allowed to be on the Wall.
In the ancient time， most towns or villages close to the Wall were habited by soldiers and their families. The nomads outside the Wall would come and trade with these people at designated markets in the name of “tribute”. For example， Mongols would sell their horses to Chinese and buy salt， tea， silk cloth etc. in return.
The traders from inside the Wall had to get permits from the government to do the business with the nomads， otherwise they would be arrested for being too close to the border.
So the situation is clear. The Great Wall will restrict traders to certain places (normally large gates in the wall) where both sides could trade with each other. The nomads can only trade with certain people (those who have permits from the government).
Also， merchants from inside the Wall could go to other countries. They also had permits from the government， otherwise they were unable to pass through the Wall.
Finally， the government could tax the traders since everything was under control (permits， designated markets etc.) That’s one way ancient China could make some money.
长城仅用作军用公路。士兵们可以动员起来，当出现紧急情况，随时随地的出动。至于平民，他们不允许上长城。
在古代，靠近长城的城镇和村庄大多由士兵和他们的家人居住。长城外的游牧民会以“贡品”的名义到指定的市场与这些人做生意。例如，蒙古人会把马卖给中国人，然后买盐、茶、丝绸等作为回报。
来自围墙内的商人必须得到政府的许可才能与游牧民做生意，否则他们会因为离边境太近而被捕。
情况很清楚。长城将会限制商人们到某些特定的地方(通常是墙上的大门口)双方可以互相交易。牧民只能与某些人（那些有政府许可的人）进行交易。
同时，长城内的商人也可以去其他国家。他们也有政府的许可，否则他们就无法通过长城。
最后，政府可以对商人征税，因为一切都在控制之中(许可证、指定市场等)，这是古代中国赚钱的一种方式。
Gwydion Madawc Williams
Gwydion Madawc Williams， Read a lot about this
Answered Jul 15， 2016
There were several Great Walls. Each of them controlled trade， among other things.
Also helped North China by making raiding a lot harder. A man could scale an undepended portion of the wall， but getting a horse over would be much tougher. Likewise getting back if pursued.
Well， let’s just take Ming dynasty as an example.
The Ming Dynasty， despite of its initial offensives back in 14th century， suffered a severe loss in the battle of Tu Mubao (The Soil-Timber Fortress) in 1449 and therefore was forced to employ passive defense behind the Great Wall.
Although such strategies worked not that effectively in the military sense as the Mongolians continued their raid， the Ming Dynasty still suspended the trade by their nine gateways， thus cut off the essentials of Mongolians in the north largely， if not completely.
It turned out then the Mongolian chefs could hardly cook because the import of iron skillets was cut off. Thus the nomads commanded by Altan Khan rushed into the interior soil again. Eventually， a trade deal was made in which both sides decided to exchange Mongolian horses for Ming’s every-day products.
So all in all here， the Great Wall influenced the economy of Ancient China as a massive embodiment of tariff.
长城有许多段，他们中的每一段都控制着贸易及一些其他事情
有几段长城。他们都控制着交易，还有其他的东西。
也帮助了中国北方，使突袭变得更加困难。一个人可以爬上一段长城，但要骑马翻过来就难多了。同样地，如果士兵被追杀，想回去也难。
让我们以明朝为例。
明朝，尽管在14世纪发动了最初的进攻，但在1449年的土木堡战役中遭受了严重的损失，因此被迫在长城后面采用被动防御。
尽管这些策略在军事意义上并没有像蒙古人继续他们的突袭那样有效，但明朝仍然以九门的方式中止了贸易，因此在很大程度上切断了蒙古人的生活必需品，如果不是完全的话。
后来，由于铁锅的进口被切断，蒙古的厨师们很难做饭。于是，阿勒坦汗指挥的游牧民族又一次冲进了内陆。最终，双方达成了一项贸易协议，双方决定用蒙古马来交换明朝的日常用品。
所以总的来说，长城作为关税的巨大体现，影响了中国古代的经济。
Zapper Li
Zapper Li
Answered Jul 14， 2016
The great wall blocked most of the accessible border for trading， so the trading merchants can only do business through some open gates which is called 关. As a result， the trade was somehow controlled and can be eventually taxed， which was a great advantage against the northern nomads.
So it didn‘t serve as trade highway but more like filter.
长城阻止开放的边境贸易，所以交易商人只能通过叫做“关”一些打开大门做生意。结果，这种贸易在某种程度上得到了控制，最终可以征税，这对北方游牧民族是一个很大的优势。
所以它不是贸易高速公路，更像是过滤器。
本文来源：https://www.quora.com
