April Fool's Day in France apparently stems back to the 16th century – if you’re in France on April Fool’s Day, don’t be surprised if children try to stick paper fish onto your back and call you a ‘Poisson d’Avril’ (April Fish). This April 1st tradition is supposed to have started in the 16th century when King Charles XIV of France changed the calendar and those who continued to celebrate the end of the New Year at the end of March were ridiculed as fools.