What is Great Wall of China?
{{Coord|40.67693|N|117.23193|E|display=title}} [[File:ShanhaiguanGreatWall.jpg|thumb|220px|The Great Wall of China, in Shanhaiguan.]] [[File:Map of the Great Wall of China.jpg|thumb|220px|The blue lines show the walls of the [[Ming Dynasty]], and the black symbols show the 9 [[garrison]]s of that dynasty.]] [[File:Ruins of the guard tower.jpg|thumb|220px|Ruins of a watchtower on the Great Wall]] The '''Great Wall of China''' is an ancient wall in [[China]]. It was finished in 1878<ref>{{Cite web|url=https://www.travelchinaguide.com/china_great_wall/facts/when-built.htm|title=When was the Great Wall of China built? 7th Century BC - 1878|website=www.travelchinaguide.com|access-date=2020-04-20}}</ref> and it was meant to protect the north of the [[empire]] of China from enemy attacks. It is the longest structure humans have ever built. It is about 21,196 kilometers long, {{convert|30|ft|abbr=off|disp=flip}} wide and 20 meters high. The earlier sections on the wall are made of compacted dirt and stone. Later in the [[Ming Dynasty]] they used bricks. There are 7,000 watch towers, block houses for soldiers. To send signals, soldiers used fire, and also smoke signals. Nineteen walls have been built that were called the Great Wall of China. The first was built in the 7th century BC. The most famous wall was built between 226 and 200 BC by the first [[Emperor of China]], Qin Shi Huang (Qin Pronounced as Chin), during the Qin Dynasty. Not much of this wall remains as people have been stealing from it. It was much farther north than the current wall. The current wall was built during the Ming Dynasty.<ref>{{Cite web |url=http://www.ccds.charlotte.nc.us/History/China/save/barrett/barrett.html |title=Construction of the Great Wall |access-date=2008-11-21 |archive-date=2008-12-02 |archive-url=https://web.archive.org/web/20081202072204/http://www.ccds.charlotte.nc.us/History/China/save/barrett/barrett.html |url-status=dead }}</ref> The wall is made of [[mortar]],<ref>https://www.smithsonianmag.com/history/sticky-rice-mortar-