The majority of dubious historical claims have at least some basis in fact. As we've seen many times here, stories about real people in the past may grow by accretion into some weird amalgam of fact and fiction, but usually there's at least a small kernel of truth buried in there somewhere. While President Taft never actually got stuck in his bathtub, and Catherine the Great of Russia didn't die while attempting to have sex with a horse, there's no doubting that Taft was seriously overweight and Catherine had a well-deserved reputation for promiscuity.
It's seldom that there's a claim of a historical figure that was widely believed to be true, and yet is one hundred percent woven from whole cloth. But that is the situation with one of the oddest stories to come out of medieval Europe -- the legend of Prester John.
The whole thing started in the twelfth century, with the German bishop and historian Otto of Freising's Chronica de Duabus Civitatibus (Chronicle of the Two Cities), published in 1145, in which he mentions in passing that he'd heard from a Syrian colleague, Bishop Hugh of Jabala, about a Christian kingdom somewhere to the east of the Byzantine Empire. It was ruled, he said, by a king called Prester (or Presbyter) John, and this monarch might be someone the crusaders could turn to for support in returning the Holy Land to Christian control.
The story attracted little attention -- mostly, of course, because no such kingdom (or king) existed -- until fifteen years later, when a letter came to Pope Alexander III, alleging to be from Prester John himself.
To say the letter was unbelievably fulsome and self-aggrandizing would be a vast understatement. Prester John bragged about how amazing his kingdom was -- the very pinnacle of Christendom. His was the wealthiest kingdom on Earth, he said, and had no poverty or violent crime. The place was governed by the wisest of counsellors, all according to (of course) the Bible. It was the home of fantastic beasts, including elephants, lions, tigers... and cyclopses. Everyone lived a life of the utmost propriety, and sexual immodesty was unheard of.
I don't know about you, but that last bit sounds a little restrictive for my tastes.
Alexander, on the other hand, thought this sounded just peachy keen, as did a good many of the other European leaders of the time. The letter was copied multiple times, and Prester John's kingdom became a stand-in for heaven on Earth. Alexander decided to try to contact this magnificent monarch, and hand-wrote a letter of greeting which he entrusted to someone named "Master Philip," who was then sent out to try to find Prester John's kingdom so he could deliver the letter.
Amazingly, Philip returned alive.
Less amazingly, he reported to Alexander that he had been unable to find Prester John's domain.
The letter Alexander had received was, of course, a forgery. To this day historians don't know who wrote it. However, it almost certainly originated somewhere in Europe -- not, as it claimed, in the "far Indies" where Prester John supposedly dwelt. But just about everyone who heard about the letter thought its contents were nothing short of the literal truth, and belief in Prester John himself attained cultlike status. Theologians preached that Prester John's armies were going to march in and rescue the disastrous Fifth Crusade, bolstering the faltering Christian control over Palestine.
That, of course, also never happened.
Astonishingly, a failed prophecy or two, an unsuccessful attempt to locate the kingdom itself, and exactly zero evidence it ever existed other than an obviously forged letter, were not enough to undermine people's belief in the legend. By the middle of the thirteenth century, concern about the Islamic control over the Middle East was superseded by the more pressing concern that the Mongols under Genghis Khan and his successors were basically running roughshod over everyone between Mongolia and eastern Europe. However, Pope Innocent IV preached that there was nothing to worry about because Prester John was going to stop the Mongol armies in their tracks.
When that also didn't happen, Innocent switched gears and said that tragically, the Mongol armies must have overrun and conquered Prester John's kingdom.
You'd think at some point, folks would have said, "Hold on a moment... maybe the problem here is that Prester John and his kingdom don't exist." But that is to seriously misjudge people's capacity for rationalizing a complete lack of evidence when they really want to believe something. When the Europeans actually talked to the Mongols, and the Mongols said they'd never heard of Prester John, instead of giving up on the idea, the Europeans basically went, "Oh, okay! We get it now! Prester John must be somewhere else!"
So -- and I swear I'm not making this up -- they decided that since he didn't live in India or central Asia, he must live in Ethiopia instead.
The legend persisted all the way into the seventeenth century, when Portuguese missionaries did a fairly thorough exploration of Ethiopia and found out that the Ethiopians (1) had never heard of Prester John either, and (2) had no interest in being converted to Catholicism. At that point, people pretty much looked around with shocked expressions and said, "Wow! I guess the whole thing was made up! Who could have guessed?"
So at long last, they got the right answer. But it took five hundred years.
I've always been astonished at how far you can be dragged along by a combination of credulity, wishful thinking, and confirmation bias, but the legend of Prester John has got to set some kind of record. Recall that there never was any real evidence of his existence; it started out from one bishop telling another, "Hey, I've heard about this guy out east..." followed by a forgery that made claims which aren't even within hailing distance of plausibility. After that, it was off to the races -- for over five centuries.
It'd be nice if we'd made some progress as a species since then, and I suppose in some ways we have, but human frailties don't just go away. However much we've learned -- and as easy as it is to laugh at the ancients for their gullibility -- we still can be pretty damn fact-resistant. After all, consider the sad state of affairs that a significant fraction of American voters think Donald Trump is honest.
I can only hope that it won't take five hundred years for them to figure that one out.