It is believed that the tradition of April Fool’s arose around 1582 in France, during King Charles IX’s reign, when the calendar switched from the Julian to the Gregorian.
This meant that the New Year was celebrated on January 1st instead of the old New Year’s Week, which ran from March 25 – April 1. However, some people, being unaware of the change due to the slow passage of news in those days, continued to celebrate New Year’s Week; as did others who were more rebellious and who refused to acknowledge the change.
These people were labeled “fools” by the general populace, were subject to ridicule and sent on “fool errands,” sent invitations to nonexistent parties, and had other practical jokes played upon them. This harassment evolved over time and a custom of prank-playing continue on the first day of April. This tradition eventually spread elsewhere like to Britain and Scotland in the 18th century and was introduced to the American colonies by the English and the French.