One popular though unlikely explanation focuses on the fool that Christ’s foes intended to make of him, sending him on a meaningless round of visits to Roman officials when his fate had already been sealed. Medieval mystery plays frequently dramatized those events, tracing Christ’s journey from Annas to Caiaphas to Pilate to Herod, then back again to Pilate. (Interestingly, many cultures have a practice, predating Christianity, that involves sending people on "fool’s errands.")

The most convincing historical evidence suggests that April Fooling originated in France under King Charles IX. Throughout France in the early sixteenth century, New Year’s Day was observed on March 25, the advent of spring. The celebrations, which included exchanging gifts, ran for a week, terminating with dinners and parties on April 1.

In 1564, however, in beginning the adoption of the reformed, more accurate Gregorian calendar, King Charles proclaimed that New Year’s Day be moved back to January 1. Many Frenchmen who resisted the change, and others who merely forgot about it, continued partying and exchanging gifts during the week ending April 1. Jokers ridiculed these conservatives steadfast attachment to the old New Year’s date by sending foolish gifts and invitations to nonexistent parties. The butt of an April Fool’s joke was known as a poisson d'Avril, or "April fish" (because at that time of year the sun was leaving the zodiacal sign of Pisces, the fish). In fact, all events occurring on April 1 came under that rubric. Even Napoleon 1, emperor of France, was nicknamed "April fish" when he married his second wife, Marie-Louise of Austria, on April 1, 1810.