Some missed the direction and celebrated on April 1, leading them to be made fun of. However, this too is disputed, especially in Britain where the calendar was not introduced until 1752.
Others have linked it to the ancient Roman festival of Hilaria, where at the end of March, people would dress up and make fun of each other.
Whatever its origins, the day has given rise to some famous – and infamous – pranks in more modern times.
Shannon Airport to be renamed
In 2014, local radio station Clare FM ran a story that Shannon Airport was to be renamed in honour of All-Ireland winning manger Davy Fitzgerald.