This theory dates back to the 18th century and comes from an English antique dealer, William Stukeley. In a letter that became famous, he had indeed written that "Hadrian's Wall (in Britain, ed) was only exceeded by the Chinese Wall, which could be visible from the Moon."
But this is impossible because, to be visible at only 100 km of altitude, a structure must measure at least thirty meters of width. But the Great Wall never exceeds 7 meters. It is therefore unthinkable to see it from the moon, at ... 380,000 km from the Earth. This would amount to trying to distinguish a needle at a distance of 38 km. Astronaut Neil Armstrong confirmed that the wall was invisible from the moon.
