April Fool’s Day has long been a socially sanctioned occasion for lighthearted pranks. Like many traditions, the roots of this celebration of tomfoolery belie its modern celebration. In fact, April Fool’s Day has a somewhat sinister origin that is seldom recognized today.

The genesis of the April Fool is said to have arisen some time during the early reign of Julius Caesar, prior to the adoption of the Julian calendar in 46 BCE. In those days, there was no month of April, and Martius (March) segued directly into Maius (May). As a means of testing the mental fortitude and gullibility of new recruits, Roman centurions used this time to perform a secret annual hazing of the rookies among their ranks.

On the last day of Martius, the greenest of the garrison were informed with great solemnity that Emperor Caesar’s beloved dog, Aprilis, had unexpectedly died that morning. The young soldiers were further told that Caesar was subsequently so distraught that he had ordered a special day of mourning for his departed pet. All citizens were to stay indoors for the entirety of the next day, with business to resume as usual the day after that. Naturally, it was added, Caesar would be highly offended if he were to see anyone, even a Roman soldier, out and about on this day of collective grief.

It was gravely understood by everyone in the Roman military that insubordination of any sort was an intolerable offense punishable by death. To willfully disobey one’s superior was to reserve one’s cross at the next crucifixion. The dimmest of the fresh soldiers would swallow the tale of Aprilis without question and stay at home the next day, whereupon their official unexcused absence would be reported directly to Caesar. Because at least several new recruits would be missing, the emperor would perceive their simultaneous absence as a political statement of overt defiance. Naturally, he routinely had such offenders arrested immediately and put to death without trial.

The ancient historian Gaius Septimus wrote that no fewer than fifty unfortunate souls were executed due to this ruse over a period of fifteen years, with Caesar unaware of any duplicity the entire time. Among veteran centurions, any naive soldier who lost his life because he believed the wild tale of a day of mourning for Caesar’s dog became known as stultus Aprilis, or an April fool. “Woe is the fool,” observed Septimus, “who mourns the death of April.”

Caesar was reportedly quite amused when he finally learned the truth about the violent hazings, especially as he had never had a dog named Aprilis (or any court pooch, for that matter). He was also impressed by the cleverness of his most loyal centurions, who had devised a way to effectively weed out soldiers who were unworthy of serving their emperor. In honor of their achievement, and in a rare display of his little-known sense of humor, Caesar incorporated Aprilius into the new calendar, inserting it between Martius and Maius. Because the existence of their cruel tradition became common knowledge, centurions moved on to other methods of hazing. The phrase stultus Aprilis, however, entered the public lexicon, whereby it became associated with exceedingly gullible behavior on the first day after the end of March. Hence, April Fool’s Day was born.

The record of subsequent April Fool’s Day observations is spotty for centuries afterward, and what little is known is of dubious credibility. The apocryphal Gospel of Mary debunks Jesus’ first miracle at a Canaan wedding feast as a misunderstanding following her son’s substitution of water for wine in a juvenile stultus Aprilis prank. Similarly, a very small minority of biblical scholars have advanced the theory that Lazarus helped his friend pull off another great gag some years later. Neither of these tales, however, are taken seriously in general academia.

The Dark Ages apparently put the kibosh on April Fool’s Day, as the era did with most other nonessential elements of learning and culture. But Chaucer’s Canterbury Tales reveals that the tradition did not altogether disappear, as evidenced by “The Miller’s Tale,” in which the character of Nicholas plays an Aprille Foolle joke on his rival (the bawdy incident involves literal arse-kissing and flatulence, which was the height of comedy in late Medieval times). Cervantes, too, references dia de los tontos de abril in Don Quixote when the title character successfully convinces Sancho Panza that the sum of 2 and 3 is 4.

Meanwhile, the artistic fervor of the Renaissance was interrupted by annual bouts of giddy buffoonery, most notably in the notorious sciocco aprile rivalry between Leonardo da Vinci and Michelangelo. It was Michaelangelo who arranged an April 1st portrait sitting for Lisa del Giocondo and encouraged the Mona Lisa subject to adopt an enigmatic expression that Leonardo found maddening. Not to be outdone, Leonardo was discovered on a later First of April to have climbed the scaffolding within the Sistine Chapel in order to scrawl minute obscenities on the ceiling for Michelangelo to discover. Only the forceful intervention of Pope Julius II put a stop to the mischief.

Not long afterward, Galileo Galilei was finding himself under increasing pressure from the Vatican to recant his public support for a heliocentric model of the solar system. A partial page from his notebooks reveals that Galileo made an unsuccessful attempt to convince Pope Urban VIII that the whole thing was an April Fool’s joke that nearly everyone had taken seriously, prompting the astronomer to perpetuate his statement as a means of avoiding embarrassment.

By the time of the Enlightenment, April Fool’s day was an entrenched practice of Western culture, with numerous examples of its observation permeating the historical record. As Benjamin Franklin put it in Poor Richard’s Almanack, “All hail the first of April, a boon for jesters, some say. Leave nothing to chance; beware that your pants may yield to thumbtack today.” Not much has changed since then, as pranksters continue to welcome April with the ritual humiliation of gullible friends.

If you’re not a fan of April Fool’s Day, at least there is little more at stake in modern times than mild embarrassment. Should you fall victim to someone’s mischief today, console yourself with the fact that the first stultus Aprilis had it a lot worse.