I started researching this on the Internet, of course, and the first ten hits on Google had the same basic information. “In 1582, Pope Gregory XIII ordered a new calendar (the Gregorian calendar) to replace the old Julian calendar.” In the Julian calendar that preceded it, the New Year was celebrated the week of 25 March through 1 April. In the Gregorian calendar it was celebrated only on 1 January. But in France, the word was slow in being disseminated, and even when it was received, many refused to accept the new calendar. So when people were found still celebrating the New Year on 1 April, they were called “fools”. They were subject to ridicule and being sent on “fool errands”. They could also be invited to nonexistent parties or have other practical jokes played on them.
As https://April-Fool.us points out, “The butts of these pranks became known as a “poisson d’avril” or “April fish” in France, because a young naïve fish is easily caught. In addition, one common practice was to hook a paper fish on the back of someone as a joke.” Once the calendar was accepted, the April Fool’s Day jokes continued.
Most of the articles went on to say that the French influenced the British to join in the merriment, but that didn’t ring true. https://Infoplease.com pointed out that England didn’t adopt the Gregorian calendar until 1752, 170 years later. (Something about the Church of England not being subject to the Pope. Hehe.) So if it wasn’t the French who brought the April Fool’s Day pranks, where did they come from?
https://Wikipedia.org had the answer:
“In Chaucer’s Canterbury Tales (1392), the ‘Nun’s Priest’s Tale’ is set Syn March bigan thritty dayes and two. Modern scholars believe that there is a copying error in the extant manuscripts and that Chaucer actually wrote, Syn March was gon. Thus the passage originally meant 32 days after [March ended], i.e. May 2, the anniversary of the engagement of King Richard II of England to Anne of Bohemia, which took place in 1381. Readers apparently misunderstood this line to mean ‘March 32’, i.e. April 1. In Chaucer’s tale, the vain cock [Chanticleer] is tricked by a fox.” So, it appears that tricks on 1 April began with the misreading of Canterbury Tales by a scribe.
By the 1850s the English were proficient in their practical jokes. I’ve included two examples for you here. Both examples are of an invitation to the “Annual Washing of the Lions” at the Tower of London. One is dated ‘Wednesday, April 1st 1857’. The other one is dated ‘Monday, April the 1st, 1856’. But if you’ll look closer, the ‘6’ in 1856 was hand-written over the original date of ‘Monday, April the 1st, 1855’. 1 April 1856 was actually a Tuesday.
The April Fool’s Day tradition was brought over to the colonies in North America, Australia and New Zealand as well.
Hmmm… I wonder if anyone would like a ticket to the Washing of the Lions this year.