It was widely rumoured and hotly disputed for many years that the Great Wall of China was the only man-made feature on the surface of the Earth that could be seen from the moon with the naked eye.
Neil Armstrong, the first man on the moon, was rumoured to have radioed back this observation to Mission Control in Houston during Apollo 11's lunar landing in July 1969.
This was three years before US president Richard Nixon's historic visit to Beijing in 1972, when he saw the Great Wall close-up.
Indeed, the purported statement by Mr Armstrong is the stuff of urban legend. The Earth is too far from the moon for any man-made object to be seen with unaided eyes, as scientists familiar with space imagery will attest.
In a recent meeting, I asked Gene Cernan, the last man to set foot on the moon, about this much-believed notion. He chuckled and told me instead about his experience of driving his lunar rover on the Great Wall during one of his visits to Beijing.
If the Great Wall could be seen from space, it would be in competition with any of the interstate freeways that crisscross America, which are just as long and much wider.