(or Revolutionary Calendar), a calendar introduced during the Great French Revolution by a decree of the National Convention on Oct. 5, 1793. It was developed by the Committee of Public Instruction under the direction of C.-G. Romme.

The French Republican calendar replaced the Christian chronology and established a new era (the first day was Sept. 22, 1792—the date of proclamation of the Republic). The year was divided into 12 months of 30 days each, and each month was divided into three decades. Five supplementary days, or Sansculottides (six in leap years), were introduced to complete the year. Every tenth day, as well as all supplementary days, was considered a nonworking day. New names were introduced for the months, taking into account the particular features of each season: the fall months were Vendémiaire, Brumaire, and Frimaire; the winter months, Nivôse, Pluviôse, and Ventôse; the spring months, Germinal, Floréal, and Prairial; and the summer months, Messidor, Thermidor, and Fructidor. The new names for the days were based on Latin cardinal numbers: primidi (first day), duodi (second day), tridi (third day), and so on.

The French Republican calendar was used through Jan. 1, 1806, when it was replaced during the Napoleonic era by the Gregorian calendar. It was reinstated during the Paris Commune and was in effect from Mar. 18 through May 28, 1871, after which it was again replaced by the Gregorian calendar. (SeeCALENDAR and the references under that article.)