The Foolish Calendar
Most of us rarely think about or question the calendar (British Summer Time, maybe, but that's a different kettle of fish). Days, months, years tick along quietly, helping us remember birthdays, holidays and deadlines. But the calendar we use today (the Gregorian calendar) has a long, surprisingly dramatic history. And within that story is a potential origin for something a bit sillier:
April Fools' Day.
The Gregorian calendar was introduced in 1582, Catholic countries adopted the new system quickly, but others dragged their feet. In France and beyond, some people celebrated the new year around the end of March or the beginning of April, as they had always done under the old Julian calendar.
Those people became the butt of the joke. Still clinging to the old dates, they were teased by their calendar-know-it-all neighbours. People played tricks, sent them on fool's errands, or even stuck paper fish to their backs and called them 'April fish' or 'Poisson d'Avril' (Atlas Obscura). Over time, this tradition of mocking the misinformed evolved into the April Fools' Day we know today.
To understand why this calendar change was such a big deal, why it left some people celebrating the wrong new year, we have to go back much further.
The Julian Calendar
Before 45 BCE, Rome used a lunar calendar that was super unreliable. The months drifted through the seasons, and adjusting it fell to priests who, unsurprisingly, often made changes for political reasons.
Julius Caesar, determined to bring order, turned to Egyptian astronomers and introduced a solar-based calendar. It was a significant upgrade. A calendar that was fixed at 365.25 days, with a leap day was added every four years to account for the extra quarter day.
This system kept things mostly aligned with the solar year. It was practical and stable. But as with many ancient (and modern) reforms, it wasn't perfect.
One of the oddities of the Julian calendar was how the Romans counted time. Rather than numbering days sequentially as we do now, they counted backwards from three key points in the month:
- The Kalends (the 1st)
- The Nones (usually the 5th or 7th)
- The Ides (either the 13th or 15th)
So, for example, what we call 10 March would have been described as "six days before the Ides of March," counting inclusively. While it sounds romantic and Ye Olde Worlde, it also sounds hella confusing.. and it was.
As part of his reform, Caesar also made some vanity edits. He renamed Quintilis as July, after himself. Later, Augustus followed suit with August. Another oddity was when it came to leap years, instead of simply adding a day at the end of February like we do now, Romans repeated the sixth day before the Kalends of March. Imagine having a birthday or anniversaries that fell on one of those dates 🥴
The Julian calendar assumed a year was 365.25 days long. But in actuality, it's closer to 365.2422. That small difference equates to about 11 minutes per year which doesn't sound like much, but over centuries it adds up. By the 1500s, the spring equinox was happening around 10 days earlier than it was supposed to.
This caused issues for the Church, particularly in calculating the date of Easter, which was tied to the equinox and the lunar cycle.
The Gregorian Calendar
In 1582, Pope Gregory XIII introduced the Gregorian calendar where ten days were removed from the calendar to realign the equinox. In countries that adopted the reform immediately, the 4th of October was followed by the 15th of October. The leap year rules were also updated: a year is a leap year every four years, unless it is divisible by 100 — except if it is also divisible by 400.
This meant that while 1600 and 2000 were leap years, 1700, 1800 and 1900 were not. These tweaks brought the calendar much closer to the solar year.
While Catholic nations adopted the Gregorian calendar right away, others were skeptical.
England and its colonies switched in 1752, by which time 11 days had to be skipped. The change caused confusion and even sparked protests. The English calendar riots of 1752 had people demanding "Give us our eleven days!" as many people mistakenly believed that their lives would be shortened by 11 days. (Historic UK).
More recently, Russia waited until after the 1917 revolution and Greece only made the change in 1923.
Even today, some Orthodox churches still use the Julian calendar for religious celebrations, which is why Christmas is observed on different days depending on the tradition.
A Foolish Legacy
So a theory for the origin of April Fools' Day is that the confusion and resistance around the calendar change over centuries created the tradition. Old Julian calendar hanger-onners were easy targets for pranks, fake invitations, tom foolery, creating The April Fool. What began as a joke about outdated customs eventually became a custom in itself.
The shift from the Julian to the Gregorian calendar was more than a technical fix. It was a collision of science, religion and politics that reshaped the way we experience time. And hidden away in that transformation is a small but enduring tradition of mischief and silliness.
Next time you laugh at a prank on April Fools' Day, you're also laughing with history. And maybe, just maybe, you're also honouring the poor sods who didn't get the memo back in the 16th century.