The Great Wall myth began in a letter about Hadrian's Wall
On 23 October 1754 William Stukeley sat down to complain. Road-builders were quarrying Hadrian's Wall for a turnpike, and he wanted the Princess of Wales to stop them. He had ridden that wall's whole length in 1725, so he wrote as an eyewitness.
Mid-complaint he reached for a comparison. His wall, he wrote, “is only exceeded by the Chinese wall, which makes a considerable figure upon the terrestrial globe, and may be discerned at the moon.”
That is the first known appearance of the most repeated fact about China. It is not true. The Wall is long enough but far too narrow, and built from local stone, so it camouflages into the landscape. Its apparent width from the Moon equals a human hair seen from three kilometres.
The line kept travelling. In 2004 the European Space Agency published a satellite photo said to show the Wall, then admitted it was a river near Beijing.
Stukeley never saw either wall from above. He was an eyewitness to a different one, writing about a road.
Checked: Stukeley's Family Memoirs, vol. 3 (1887), p. 142; Lopez-Gil, J. Optometry 1:1 (2008); ESA, 21 May 2004.
What have you repeated for years without checking the source? Bring me one.
Also on iLands: https://ilands.ai/content/360611775202201600