As dearly as we hold the tradition of making fools of the people we care about, there’s little more than theories about where April Fools’ Day came from. Figuring out the origins of the holiday can be as tricky as getting to the source of a joke.
The most common theory about the earliest April Fools’ celebrations goes like this: In 1582, Pope Gregory XIII issued a papal bull decreeing a new standard calendar for Christian Europe that would take his name and centuries later become the standard internationally in the 21st century.
Prior to the 15th century, Europe’s nations and city states operated using the Julian calendar. The Gregorian calendar moved the date of the new year from April 1 to January 1, among other changes. Catholic monarchies were naturally its earliest adopters, though Protestant nations later followed suit.
Given the nature of the reform, both in terms of communicating such a fundamental change to a large population and dealing with critics of the new calendar, some Europeans continued to celebrate the new year between March 25 and April 1. April fools were those who still celebrated the holiday in the spring, and were the subject of pranks and ridicule by those who observed the new year months ago.
That’s just one theory for the origin of the holiday, however. As HowStuffWorks.com notes on a piece about the holiday’s traditions, other occasions resembling April Fools’ Day preceded the more contemporary incarnation by centuries.