Great Wall of China

To aid in defense, the Great Wall utilized watchtowers, troop barracks, garrison stations, signaling capabilities through the means of smoke or fire, and its status as a transportation corridor. Other purposes of the Great Wall have included border controls (allowing control of immigration and emigration, and the imposition of duties on goods transported along the Silk Road), and the regulation of trade.
The collective fortifications constituting the Great Wall stretch from Liaodong in the east to Lop Lake in the west, and from the present-day Sino - Russian border in the north to Tao River in the south: an arc that roughly delineates the edge of the Mongolian steppe, spanning in total. It is a UNESCO World Heritage Site, and was voted one of the New 7 Wonders of the World in 2007. Today, the defensive system of the Great Wall is recognized as one of the most impressive architectural feats in history. Provided by Wikipedia
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