It is uncertain how All Fool's Day a.k.a. April Fool's Day began. Of course, there are many theories explaining its origins:
1.) The Calendar-Change Theory - This one is the most popular one. In 1582 France became the first country to switch from the Julian to the Gregorian calendar. The New Year once fell on March 25th, but since that day fell in the Holy Week, New Year festivals were on April 1st. After the change, those who could be tricked into believing April 1st was still the proper day to celebrate the New Year earned the name April Fools and would have pranks played on them.
The calendar change theory might provide a plausible 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. 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 evidence, besides conjecture, supports the theory. For which reason, while there's certainly a possibility that the calendar-change hypothesis contains a germ of truth, it should not be regarded as fact.
2.) The Saturnalia, a Roman winter festival observed at the end of December, was the most important celebration of foolery and trickery, involving 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.
3.) In India there was the festival of color known as Holi. To celebrate, they 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).
4.) Some people have even tried to tie it to Biblical times. Some believe the day derived from Noah's mistake of sending out a dove from the ark before the flood waters subsided, sending the dove on a fool's errand. Another version tells of when Jesus was sent from Pilate to Herod and back again. The phrase "Sending a man from Pilate to Herod" (an old term for sending someone on a fool's errand) was often pointed to as proof of this origin theory.
5.) There are rival mythological explanations linking the celebration to pagan roots. The day was often traced back to the myth of Ceres and Proserpina from Roman mythology. Pluto, the God of the Dead, abducted Proserpina and brought her to live with him in the underworld. Proserpina called out to her mother Ceres for help, but Ceres could only hear the echo of her daughter's voice and therefore, searched in vain for Proserpina. The fruitless search of Ceres for her daughter (commemorated during the Roman festival of Cerealia) was believed by some to have been the mythological antecedent of the fool's errands popular on April 1st.
6.) British folklore states that April Fool's Day is linked with the town of Gotham, the legendary town of fools located in Nottinghamshire. It was traditional in the 13th century for any road that the King placed his foot upon to become public property. So when the citizens of Gotham heard that King John planned to travel through their town, they refused him entry, not wishing to lose their main road. When the King heard this, he sent soldiers to the town. But when the soldiers arrived in Gotham, they found the town full of lunatics engaged in foolish activities such as drowning fish or attempting to cage birds in roofless fences. Their foolery was all an act, but the King fell for the ruse and declared the town too foolish to warrant punishment. And ever since then, April Fool's Day has supposedly commemorated their trickery.
Despite its' unknown origins, like many holidays, this day also has superstitions linked to it. The first being that the pranking period expires at noon. Any jokes attempted after that time would bring the prankster bad luck. Another one states that those who fail to find humor in the tricks played on them will also attract bad luck. However, men are advised not to marry on this day or their wives will rule them forever.
On a more positive note, guys who are fooled by a pretty girl are said to be fated to end up married or at least have a healthy friendship with her. Children born on 1st of April are considered lucky generally, except in gambling where they will fare badly.
On this day, tricks range from gag gifts and prank phone calls to elaborate hoaxes. Check out the Museum of Hoaxes website for the top 100 April Fool's Day hoaxes.
Since it is April Fool's Day, I leave you with a riddle (I'll reveal the answer tomorrow):
You are an expert on paranormal activity and have been hired to locate a spirit haunting an old resort hotel. Strong signs indicate that the spirit lies behind one of four doors. The inscriptions on each door read as follows:
Door A: It's behind B or C
Door B: It's behind A or D
Door C: It's in here
Door D: It's not in here
Your psychic powers have told you three of the inscriptions are false, and one is true. Behind which door will you find the spirit?
Sources: Snopes, The Museum of Hoaxes and April Fool's Day