Great Wall of China
The Great Wall of China is not one wall but a mosaic of fortifications built, rebuilt and abandoned over some two millennia along China's northern frontier. Its earliest sections date to the 7th–4th century BCE, in the Spring and Autumn and Warring States periods; in 221 BCE Qin Shi Huang connected existing walls into a single system, and later dynasties — most famously the Ming (1368–1644) — extended and faced the line with brick and stone. The most authoritative modern figure comes from a state survey conducted since 2007: the State Administration of Cultural Heritage announced in June 2012 that all sections of the wall total 21,196.18 kilometres; the Ming wall alone is about 8,850 km, per Britannica, running from Mount Hu near Dandong to Jiayu Pass in Gansu. UNESCO inscribed the Great Wall as a World Heritage site in 1987 and calls it an absolute masterpiece of military architecture; protection today rests on the 2006 Regulations on the Protection of the Great Wall, a 2019 conservation plan, the national cultural park programme, and provincial laws such as Shanxi's 2026 regulations. The popular claim that the wall is visible from space — or from the Moon — is a myth: NASA, National Geographic and Britannica all state it is not visible to the naked eye from the Moon and is difficult or impossible to see from Earth orbit without high-powered lenses.