“(as judged by notoriety, absurdity, and number of people duped)” (The Museum of Hoaxes) The article also has a link to this page, about speculation about the origins of April Fool’s Day. An interesting theory connects it to the calendar reform in 16th century Europe. Those who declined to switch from the Julian to the Gregorian calendar, and thus continued to celebrate the new year at the end of March instead of the newly decreed day of January 1st, were supposedly subject to ridicule and practical jokes at that time.