The reason April 1 is April Fool’s Day is probably connected to the change from the Julian to the Gregorian calendar. Before the Gregorian calendar was introduced, people in some parts of Europe celebrated the New Year and exchanged gifts on April 2. New Year’s Day was officially moved to January 1 after the adoption of the Gregorian calendar in 1582. People who forgot about the change were often mocked by their friends, as they continued to make New Year visits just after the old date. Those who failed to keep up with the change and celebrated the New Year during the week that fell between March 25 and April 1 became victims of various jokes. For example, pranksters would discreetly stick paper fish to their backs. The victims of this prank were called Poisson d'Avril, or April Fish.