In the 16th Century all the people believed that 1st April is the New Year’s Day according to the Julian calendar. But people Gregory XIII introduces a new calendar in Feb 1582 and he said that Jan 1st is the start of a new year. Some of them believed his opinion. But most of them didn’t.
So they planned to do something to the believers group.
So they sent a box to every believer’s house. When they opened the box there is a paper written ‘April Fool’.
France is the 1st country to celebrate April fool’s day. Then after some years most of the people believed Pope Gregory’s Opinion and followed Gregorian calendar and today every country is following Gregorian calendar.
But, today also we are celebrating April fool’s day!