April Fool's Day is the day for pranksters and worse for the victims of those pranks. But have you ever wondered where this tradition originated? There are numerous explanations as to the origin of this day; here are the most popular ones. The most common theory behind the origin of April Fool's Day is the calendar switch that happened in Europe around 1500s. In 1582, Pope Gregory XIII decided to switch calendars, from the Julian to Gregorian calendar. According to the Julian one, New Year's Day fell on April 1 but the Gregorian one had it on January 1. People who were slow to realise this change and continued to celebrate New Year's Day on April 1 were made fun of. They were called Poisson d'Avril (April Fish) and paper fish were stuck to their backs without their knowledge.

Another explanation is the festival of Hilaria, an ancient Roman celebration for the resurrection of the god Attis.

The word Hilaria resembles the word hilarity in english, meaning extreme amusement. Also, the modern equivalent of Hilaria is called Roman Laughing Day.

Yet another possible explanation is the association between April 1 and devious trickery in one of the Canterbury Tales (1392), The Nun's Priest's Tale.

It's a story of a fox who tricks a rooster into becoming his meal, but then he himself is tricked by the rooster into letting him go. The opening lines of the story mention 'Syn March bigan thritty dayes and two', which is misunderstood to mean April 1.