A French April Fools’ origin theory cites the Edict of Roussillon in 1564.
The theory connects April Fools’ Day with a change in the date used to begin the year. Before France standardized New Year’s Day, different regions recognized dates such as Christmas, 25 March, Easter, or 1 March. The Edict of Roussillon, issued under King Charles IX, established 1 January as the start of the year across the kingdom.
Because some people supposedly continued following older customs, the theory says that those observing the old New Year around late March or 1 April became targets of jokes. This is often presented as an explanation for the “April fool” tradition, but it is not proven. A 1561 Flemish poem already describes a nobleman sending a servant on foolish errands on 1 April, before the edict.
The edict was promulgated at Roussillon on 9 August 1564, but its new-year rule began to be applied on 1 January 1567. The date is therefore important both for French calendar history and for a frequently repeated—but disputed—origin story about April Fools’ Day.