Today in France, people who are fooled on April 1 are called Poisson d'Avril, which literally means the "April Fish."

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Holidays are celebrated for all sorts of reasons. Some honor heroes, others commemorate religious events, but April 1 stands out as the only holiday that celebrates foolishness. April Fools' Day, or All Fools Day, is an odd celebration with a strange history. What other holiday asks us to play tricks and dupe our unsuspecting friends and acquaintances?

There's some uncertainty about when and where thisĀ­ bizarre tradition began, but the most accepted explanation traces April Fools' Day back to 16th century France. Up until 1564, the accepted calendar was the Julian calendar, which observed the beginning of the New Year around April. According to "The Oxford Companion to the Year," King Charles IX then declared that France would begin using the Gregorian calendar, which shifted New Year's Day to January 1.

Not everyone accepted this shifting of dates at the same time. Some believed that the dates should not be shifted, and it was these people who became the butt of some April jokes and were mocked as fools. People sent gifts and invited them to bogus parties. Citizens in the rural parts of France were also victims of these jokes. In those days, news traveled slowly and they might not have known about the shifting of dates for months or years. These people also endured being made fun of for celebrating the new year on the wrong day.

Today in France, people who are fooled on April 1 are called Poisson d'Avril, which literally means the "April Fish." One common joke is to hook a cardboard fish to the back of a person. What a fish has to do with April Fools' Day is not clear. Some believe that the fish is tied to Jesus Christ, who was often represented as a fish in early Christian times. Others say the fish is related to the zodiac sign of Pisces, which is represented by a fish, and falls near April. It's interesting to point out that Napoleon earned the Poisson d'Avril monicker when he married Marie-Louise of Austria on April 1, 1810.

It's probably no coincidence that April Fools' Day is celebrated at the same time that two other similar holidays are celebrated. In ancient Rome, the festival of Hilaria was thrown to celebrate the resurrection of the god Attis. Hilaria is probably the base word for hilarity and hilarious, which mean great merriment. Today, Hilaria is also known as Roman Laughing Day. In India, the Holi festival celebrates the arrival of spring. As a part of that festival, people play jokes and smear colors on each other.

There's no clear connection between the modern observance of April Fools' Day and these two ancient celebrations, which lends most historians to accept the French explanation for how April Fools' Day developed.

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