1. You can see it from space
Robert Ripley's tag-line - "Believe It or Not!" - was a great way of trundling out alluring half-truths, and it was this American amateur anthropologist who widely publicised the notion in 1932 that the Great Wall "would be" the only man-made structure visible from the moon. His assertion became an instant urban myth, re-spun by a generation of commentators and Sinologists who should have known better.
The moon is 384,400 kilometres from Earth, and space travel didn't become a reality until quite some time after Ripley's demise in 1949. So while being able to discern continents and oceans, despite craning their necks astronauts - including China's official "Space Hero" Yang Liwei - have been unable to pick out a wavy line of piled-up rocks.
2. It's called the Great Wall
Folklore has it that another American, President Richard Nixon, purportedly stuck for words during his 1972 visit, declared that he reckoned the Great Wall certainly was a great wall. Few English-language guide books call the structure anything else, and like Eiffel Tower or Empire State Building, it's an iconic term that requires little explanation.
It's not called Great Wall, leastways not by 1.3 billion-plus Chinese, a few dozen tour guides excepted. Most refer to it as Chang Cheng, or Long Wall, which can also be translated as Long City. Some records mention (erroneously) The Ten Thousand Mile Long Wall. Chinese poets go for The Purple Wall or The Earth Dragon. Bonus trivia: Great Wall wine is an acquired taste.
3. It's ancient
Scour the history books and references to the Wall start popping up as early as 771 BC. China's first emperor, Qin Shi Huang, was a terrific fan, building from Gansu as far as Manchuria, and subsequent dynasties pushed it further west, especially the Qi, who had added some 1,600 kilometres by 574AD.
The Wall as it appears today - a sort of Oriental Hadrian's - dates from the 15th century. Earlier efforts were no more than earth ramparts and dykes. And much of the original Wall has disintegrated. Tourist spots such as Badaling, northwest of Beijing, were rebuilt in recent years to attract visitors. A now-defunct tourist board scheme inviting foreigners to physically help with reconstruction is believed to have been an elaborate practical joke.
4. It was impenetrable
Safeguarding the northern reaches of China, lined with battlements and intersected by strategically placed turrets, up to nine metres thick and eight metres high, garrisoned by crack infantry and cavalry regiments, supplied with enough food and arms to repel a lengthy siege, the Wall was an impassable barrier which kept the marauding hordes at bay down the centuries.
That's all well and good, unless a traitor decides to open one of the gates, as happened at the far eastern outpost of Shanhaiguan in 1644. The Manchu armies swarmed though, marking the start of a dynasty that was to hold sway over China until 1912. Moral - stone walls do not a fortress make.
5. It's filled with bodies
Whatever the date in history, the clarion call for volunteer masons, bricklayers or indeed common-or-garden wielders of pick and shovel met with little response. Forced labour was the solution, up to a million at a time according to some estimates, and if some of them pegged it on the spot, there was one obvious and handy site for interment.
No bones or indeed other indication of human remains have been found in the Wall. The most likely source of the rumour is a historian with a grudge against the previous regime. Still, it's a cracking story to make attention-wavering tourists sit up and take notice.