The Great Wall is many walls, and Marco Polo never mentioned any
There was never one Great Wall. Rival states started building border walls in the 7th century BC, the First Emperor stitched some together, and later dynasties added their own. The famous brick ramparts near Beijing are Ming work, not Qin, and the whole system adds up to about 21,196 km.
Wall-building was already familiar during the Spring and Autumn period. States such as Qin, Chu and Zhao raised barriers of stone or stamped earth packed between boards, strong enough to stop swords and spears. When Qin unified China in 221 BC, its ruler tore down the walls dividing the old states but linked the northern ones against the Xiongnu. Builders used whatever lay nearby, stone in the mountains and rammed earth on the plains, and most Qin sections have since eroded away.
After Qin, rulers avoided the name Long Wall because it evoked the First Emperor's reputation for tyranny, calling their additions frontiers, ramparts or border walls, or poetically the Earth Dragon. Only under the Qing did one term cover them all. The Chinese name Ten-Thousand Mile Long Wall uses ten thousand to mean countless, much like the English myriad.
The Ming did the most. After their defeat by the Oirats at Tumu, they built in brick and stone, perhaps adding up to 25,000 watchtowers; general Qi Jiguang oversaw 1,200 of them between 1567 and 1570. Yet walls did not decide the dynasty's fate. In 1644, with Beijing already taken by rebels, the Ming general Wu Sangui opened the gates at Shanhai Pass to the Manchus, hoping they would drive out the rebels. They took Beijing instead and founded the Qing.
European fame came late. Visitors in the 13th and 14th centuries, Marco Polo and William of Rubruck among them, never mentioned the wall. Portuguese writers began describing it in the 16th century, and in 1605 the Jesuit Bento de Gois may have been the first European recorded entering China through it, at Jiayu Pass. Later Western accounts drifted into exaggeration, including the false but widespread idea that the Ming walls were the First Emperor's originals.
Source: Great Wall of China
