The French Republican calendar (calendrier républicain français), also commonly called the French Revolutionary calendar (calendrier révolutionnaire français), was a calendar created and implemented during the French Revolution, and used by the French government for about 12 years from late 1793 to 1805, and for 18 days by the Paris Commune in 1871, and meant to replace the Gregorian calendar.
The revolutionary system was designed in part to remove all religious and royalist influences from the calendar, and was part of a larger attempt at decimalisation in France (which also included decimal time of day, decimalisation of currency, and metrication). It was used in government records in France and other areas under French rule, including Belgium, Luxembourg, and parts of the Netherlands, Germany, Switzerland, Malta, and Italy.
The National Constituent Assembly at first intended to create a new calendar marking the "era of Liberty", beginning on 14 July 1789, the date of the Storming of the Bastille. However, on 2 January 1792 its successor the Legislative Assembly decided that Year IV of Liberty had begun the day before. Year I had therefore begun on 1 January 1789.
On 21 September 1792, the French First Republic was proclaimed, and the new National Convention decided that 1792 was to be known as Year I of the French Republic. It decreed on 2 January 1793 that Year II of the Republic had begun the day before. However, the new calendar as adopted by the Convention in October 1793 made 22 September 1792 the first day of Year I.
Ultimately, the calendar came to commemorate the Republic, and not the Revolution. The Common Era, commemorating the birth of Jesus Christ, was abolished and replaced with 'l'ère républicaine', the Republican Era, signifying the "age of reason" overcoming superstition, as part of the campaign of dechristianization.
The First Republic ended with the coronation of Napoleon I as Emperor on 11 Frimaire, Year XIII, or 2 December 1804. Despite this, the republican calendar continued to be used until 1 January 1806, when Napoleon declared it abolished.