The origin of April Fool's Day remains clouded in obscurity. Basically no one knows exactly where, when, or why the celebration began. What we do know is that references to 'All Fool's Day' (what April Fool's Day was first called) began to appear in Europe during the late Middle Ages. All Fool's Day was a folk celebration and elite participation in it appears to have been minimal (which is why it's so difficult to trace the exact origin of the day, because the people celebrating it back then weren't the kind of people who kept records of what they did). But what is clear is that the tradition of a day devoted to foolery had ancient roots. As we look back in time we find many ancient predecessors of April Fool's Day.
Ancient Roots
Throughout antiquity numerous festivals included
celebrations of foolery and trickery. The Saturnalia, a Roman winter festival
observed at the end of December, was the most important of these. It involved
dancing, drinking, and general merrymaking. People exchanged gifts, slaves were
allowed to pretend that they ruled their masters, and a mock king, the
Saturnalicius princeps (or Lord of Misrule), reigned for the day. By the fourth
century AD the Saturnalia had transformed into a January 1 New Year's Day
celebration, and many of its traditions were incorporated into the observance of
Christmas.
In late March the Romans honored the resurrection of Attis, son of the Great Mother Cybele, with the Hilaria celebration. This involved rejoicing and the donning of disguises.
Further afield in India there was Holi, known as the festival of color, during which street celebrants threw tinted powders at each other, until everyone was covered in garish colors from head to toe. This holiday was held on the full-moon day of the Hindu month of Phalguna (usually the end of February or the beginning of March).
Northern Europeans observed an ancient festival to honor Lud, a Celtic god of humor. And there were also popular Northern European customs that made sport of the hierarchy of the Druids.
All of these celebrations could have served as precedents for April Fool's Day.
Medieval Roots
During the middle ages, a number of celebrations developed which served as
direct predecessors to April Fool's Day. The most important of these was the
Festus Fatuorum (the Feast of Fools) which evolved out of the Saturnalia. On
this day (mostly observed in France) celebrants elected a mock pope and parodied
church rituals. The church, of course, did its best to discourage this holiday,
but it lingered on until the sixteenth century. Following the suppression of the
Feast of Fools, merrymakers focused their attention on Mardi Gras and
Carnival.
The Most Popular Theory About the Origin of April Fool's Day
The most widespread theory about the origin of April Fool's Day involves the
Gregorian calendar reform of the late sixteenth century. Although popular, this
theory has a number of problems with it.
The theory goes like this: In 1582 France became the first country to switch from the Julian to the Gregorian calendar established by the Council of Trent (1563). This switch meant, among other things, that the beginning of the year was moved from the end of March to January 1. Those who failed to keep up with the change, who stubbornly clung to the old calendar system and continued to celebrate the New Year during the week that fell between March 25th (known in England as Lady Day) and April 1st, had various jokes played on them. For instance, pranksters would surreptitiously stick paper fish to their backs. The victims of this prank were given the epithet Poisson d'Avril, or April Fish. Thus, April Fool's Day was born. (See above for an alternative story about the origin of the term 'Poisson d'Avril').
The calendar change hypothesis might provide a reason for why April 1st specifically became the date of the modern holiday. But it is clear that the idea of a springtime festival honoring misrule and mayhem had far more ancient roots. In addition, the process by which the observance of the day spread from France to protestant countries such as Germany, Scotland, and England is left unexplained by this theory. These nations only adopted the calendar change during the eighteenth century, at a time when the tradition of April Foolery had already been well established throughout Europe. Finally, it is not clear what, if any, primary evidence (i.e. first-hand accounts written during the 16th and 17th centuries) supports the theory. The link between the calendar change and April 1st appears to be based on modern conjecture rather than archival research. Therefore, while the theory remains a possibility, it should not be treated as a fact.