In "The Adventures of Marco Polo" (1938), Gary Cooper asked a Chinese friend about the sticks of dough he'd seen people cooking. His informant helpfully explained, "We call them spa get."
There was a joshing note in the answer, but it assumed that everybody knew Marco Polo would introduce pasta to Italy on his return from China. Nowadays, we know he did no such thing. A lot of people have noticed that Polo's book refers to "lasagna and other pasta dishes." Obviously, since he had a name for pasta, the folks back home already knew about it.
The Polo pasta myth originated in a story titled "A Saga of Cathay," which appeared in the October 1929 issue of the Macaroni Journal, a trade magazine of North American pasta makers. It tells how an Italian sailor was sent ashore on a small Chinese island to fill a cask with water. In the courtyard of a house, he saw a young woman cooking "strings" and indicated by gesture that he wanted to try them.
Back aboard ship, he showed these tasty strings to Polo, who happened to be a passenger. Polo went ashore, got the recipe and made them for the ship's captain and cook. Everybody was so pleased that they decided to name them after the sailor, whose name, coincidentally, was Spaghetti.
If they had read the original story, most Americans in 1929 could have recognized PR myth-making at work; in the '20s, ads often took the explicit form of fairy tales. (How believable was it for an Italian ship to be sailing around in China 200 years before Vasco da Gama found the sea route to Asia? And come on--sailor Spaghetti?)
But the story entered folklore. In retelling, the transparently bogus literary elements fell away and what was left was a plausible-sounding tale that appealed to our love of the marvelous and of stories connecting famous dishes with famous people.