Le Calendrier Répulicain: A Revolutionary Calendar

A special thanks to Kevin Moore, Grainger Graduate Assistant, for creating this exhibit.


Calendrier-republicain-debucourt2, By Debucourt, Philibert Louis (Bibliothèque nationale de France) [Public domain], via Wikimedia Commons
Calendrier républicain
By Debucourt, Philibert Louis (Bibliothèque nationale de France)

[Public domain], via Wikimedia Commons






During the height of the French Revolution in 1793, France’s National Convention set out to replace the widely used Gregorian calendar with a new version divorced from any Christian associations and instead grounded in logic and reason. The result was the French Republican calendar.

The design drew inspiration from a similar calendar proposed by French poet and playwright Pierre-Sylvain Maréchal in 1788. All 12 months received new names and the beginning and ending days of each month were changed to better align with the various equinoxes and the changing seasons. The calendar was implemented on October 5, 1793 and received and official, backdated starting day of 1 Vendémiaire, year I (September 22, 1792 according to the Gregorian calendar).

France soon became disenchanted with its new calendar through. Transposing dates between the French Republican calendar and the Gregorian calendar complicated communications with other countries and France formally switched back to the Gregorian calendar on January 1, 1806.

When it came to the technical design of the French Republican calendar, the National Committee enlisted the help of two prominent mathematicians. Joseph-Louis Lagrange (seminal figure in number theory and analytic and celestial mechanics) and Gaspard Monge (inventor of descriptive geometry) collaborated to create the new system.

The mathematicians’ final design consisted of 12 months of 30 days each. Every month consisted of three, 10-day décades instead of weeks. The final five days of each 365-day year were set aside for vacations and festivals before the autumnal equinox. Leap days could be added as one more festival day, signifying the end of another four-year period know as Franciade.

Historical information about the calendar came from the following:

A special thanks to Kevin Moore for creating this exhibit.

Books on Display

  1. [Cours de mathématiques à l’usage de l’École centrale des quatre-nations] / par S.-F. Lacroix. v.1 (Math 510 L112C)
  2. Application de l’analyse à la géométrie, par G. Monge. (Math 516.3 M74A)
  3. Journal. v.1(1795-1796) (Math [non-circulating] 505 JO)
  4. Kalenderarithmetik / Heinz Bachmann. (Math 529.7 B124K)
  5. Théorie des fonctions analytiques : contenant les principes du calcul différentiel, dégagés de toute considération d’infiniment petits, d’évanouissants, de limites et de fluxions, et réduits à l’analyse algébrique des quantités finies (Math 515.9 L13T1847)
  6. Untersuchungen zur Geschichte der tibetischen Kalenderrechnung / von Dieter Schuh. (Math 529.3 SCH79U)
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