Some newspapers, magazines, and other published media report fake stories, which are usually explained the next day or below the news section in small letters. Although popular since the 19th century, the day is not a public holiday in any country.

In 1582, Pope Gregory XIII ordered a new calendar (the Gregorian Calendar) to replace the old Julian Calendar. The new calendar called for New Year's Day to be celebrated 1 January. 

That year, France adopted the reformed calendar and shifted New Year's day to 1 January.

According to a popular explanation, many people either refused to accept the new date, or did not learn about it, and continued to celebrate New Year's Day on 1 April.

Another explanation of the origins of April Fools' Day was provided by Joseph Boskin, a professor of history at Boston University. He explained that the practice began during the reign of Constantine, when a group of court jesters and fools told the Roman emperor that they could do a better job of running the empire.

Constantine, amused, allowed a jester named Kugel to be king for one day. Kugel passed an edict calling for absurdity on that day, and the custom became an annual event.

"In a way," explained Prof. Boskin, "it was a very serious day. In those times fools were really wise men. It was the role of jesters to put things in perspective with humor."

This explanation was brought to the public's attention in an Associated Press article printed by many newspapers in 1983.

There was only one catch: Boskin made the whole thing up. It took a couple of weeks for the AP to realize that they'd been victims of an April Fools' joke themselves.

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