Every year on April 1, when jokesters pull out their best pranks and hoaxes, you may have asked yourself: How did this weird tradition start, anyway? The answer is ... no one really knows. In fact, the origins of April Fools’ Day have long been caught up in myth and legend.

The Many Origins of April Fools' Day

Some have taken the origin back to Noah sending out the dove before the flood was over, or the Roman festival Saturnalia. One popular 19th-century hypothesis traces it to the French term poisson d’avril, literally meaning “fish of April” but figuratively meaning April Fools. The hypothesis went that poisson is a corruption of passion, and was originally in reference to part of the Passion Plays of the Easter season—specifically to commemorate Jesus’s going “backwards and forwards from Annas to Caiaphas, from Caiaphas to Pilate, from Pilate to Herod, and from Herod back again to Pilate,” in the words of one 1854 book.

Then, in 1983, an intrepid AP reporter interviewed a professor at Boston University about the history of the day. The professor initially said he didn't know anything, but—after the reporter pushed for information—he told a story about the Roman Emperor Constantine and his court jesters.

According to the professor, Constantine was told by his court jesters that they would make better rulers than him, and rather than immediately feeding everyone to the lions, Constantine allowed his jesters to rule for a day. The King of the Fools, someone named Kugel, made a proclamation that “only the absurd would be allowed on that day,” and April Fools' Day was born.

Mystery solved, right? Wrong. Unfortunately for the reporter, it turned out the professor was having a bit of fun. A little over two weeks after the article appeared, the professor admitted he had invented Kugel. “I made up the story because it comported with April Fools’ Day," the professor said, "and I don’t know what all the hullabaloo is about.” 

That was the end of the road for Kugel, and there's little to no evidence for any of the other theories, either. Instead, the most popular theory has to do with calendars.

A Calendar of Fools

There are a few versions of the calendar story, but the most popular takes the story to France in general, and the 16th century in specific. In the 1560s, Charles IX issued an edict which, among many other things, pinned the New Year to the first of January.

According to proponents of the calendar change hypothesis, the old New Year was celebrated on March 25th with a week-long party ending on April 1. Some people weren’t caught up on this date change, and thus had their week-long celebration at the end of March—and because of this became known as April Fools.

There are a few problems with this hypothesis, though. The edict was real, and really did move the date to January 1. But in a piece for the Library of Congress, Stephen Winick points out that the proponents don’t give evidence of that critical week-long party or that this confusion actually happened. Even worse, the old French New Year wasn’t on March 25th.

There wasn’t one universal New Year in France—various regions would celebrate various dates—but the conventional New Year was Easter. According to 19th century historian Sir Francis Palgrave, this is a problem in historical research, as some French years could have two Aprils.

The story works better for the United Kingdom’s (and her colonies’) switch from the Julian to Gregorian calendars in 1752—which also came with a New Year move from March to January—but April Fools was already known by then. In The Spectator from April 1711, the English essayist Joseph Addison wrote, “this little triumph of the understanding, under the disguise of laughter, is no where more visible than in that custom which prevails every where among us on the first day of the present month, when every body takes it in his head to make as many fools as he can,” before launching into a tale of a prank Addison’s neighbor played on Addison’s landlady. He wrote “every one of her children [was sent] upon some sleeveless errand, as she terms it”—such as her daughter being sent to hunt after a monster—“and, in short, the whole family of innocent children made April Fools.”

Today, it’s generally agreed that April Fools has its origins in France. And possibly those “sleeveless errands.”

April Fools' and the Mackerel

Poisson d’avril didn't originally mean an April Fool. Starting in the 15th century, it meant go-between—likely because of the two French meanings of maquereau. According to the Oxford Companion to the Year, both meanings came to French via Dutch: one being makreel, meaning "mackerel" (the fish), and the other being makelaar, meaning "broker." Though other explanations for the double meaning of maquereau exist, according to The Entertaining Magazine, another name for the mackerel was poisson d’avril, because it was “a fish easily caught by deception, singly, as well as in great shoals, at this season of the year.”

As the years went on, poisson d’avril came to mean a person who was the go-between for matchmaking (possibly to distance itself from the more unsavory meaning of maquereaupimp). Then, the theories go, people began playing pranks on these go-betweens, or making them take increasingly ridiculous missions in the name of love. According to The Museum of Hoaxes, the first unambiguous reference to April Fools Day is from a 1561 Flemish story about a nobleman sending a servant on ridiculous errands to prepare for a wedding feast. Even today, many Flemish speakers call April 1 verzenderkesdag, which the Museum of Hoaxes translates as "errand day."

Sadly, as with all such theories, the lessons of 1983 should be kept in mind. The young reporter who told the world about Kugel, King of Fools, was Fred Bayles, and today, he's an Associate Professor in the College of Communications at Boston University—the very institution he reached out to about the origin of April Fools' Day. In 2009, Bayles reflected on the controversy in an interview with BU Today. "Be very, very wary of what someone, particularly someone talking about April Fools' Day, tells you," he advised. And that’s good advice for everyone.