The Great Wall is a system of fortifications totaling 21,196.18 kilometers from Liaodong to Lop Lake, and the name itself is a 19th century European label. Chinese sources used Changcheng, long wall, with a character first meaning a city rampart, and Wanli Changcheng, where ten thousand meant countless. Warring states such as Qi and Qin built earth walls against each other until Qin Shi Huang unified China in 221 BC, tore down the internal walls, and linked the northern ones against the Xiongnu. Builders used local stone or rammed earth and moved on, and later the Han and Sui repaired walls while the Tang and Song largely ignored them.

After the 1449 disaster at Tumu, where the Oirats captured the Ming emperor, the Ming built in brick and stone with an estimated 25,000 watchtowers, including 1,200 raised under Qi Jiguang in three years, bound with mortar of slaked lime and sticky rice. In 1644 general Wu Sangui opened Shanhai Pass to the Manchus, and the Qing let the wall fall out of military use. Marco Polo never mentioned it, Bento de Góis reached Jiayu Pass in 1605, and William Stukeley claimed in 1754 it could be seen from the moon. A 2012 survey found 22 percent of the Ming wall gone.

• How amylopectin in sticky rice gave Ming mortar strength and a little flexibility
• The false legend of workers’ bones mixed into the mortar
• Why a nine meter wall cannot be seen from the moon, and Yang Liwei’s report from orbit
• Bricks stolen and sold for as little as 50 renminbi, and a 2023 excavator shortcut in Shaanxi
• Concrete paving over a wild section in Liaoning in 2014, and a daily cap of 65,000 visitors at Badaling