Although the French Revolution is often considered to have begun on July 14th 1789 with storming of the Bastille, the period of radical change associated with Robespierre's terror and the guillotine did not begin until after the tumultuous summer of 1792, when the new, largely Jacobin legislative assembly called the National Convention sat for the first time and immediately proclaimed France a republic. One year after that proclamation, on September 20th 1793, a mathematician named Gilbert Romme presented his proposal for a completely new calendar. It was a period marked by a strong sense of new beginnings and radical reform in many areas of public and private life in France. The Catholic church that had been such a dominant force in pre-revolutionary France had come to be seen as 'anti-revolutionary' and the Gregorian Calendar, with its saint's days and religious holidays, was a powerful symbol of that church's underlying influence. Romme had been commissioned to provide "a more scientific division [of the year], more in phase with the movements of the heavens, the seasons and tradition." The result was implemented for thirteen years between 1792 and 1805¹ and is known to history as The French Revolutionary Calendar.

A 'rational' calendar

The year would no longer begin on January 1st, but at the autumn equinox and anniversary of the proclamation of the Republic, September 21st. Each month was thirty days long, divided into three 'decades' of ten days each. Each 'metric' day was into ten hours of a hundred minutes of a hundred seconds. The ten days of the 'decade' were called: primidi, duodi, tridi, quartidi, quintidi, sextidi, septidi, octidi, nonidi and décadi. Every décadi was a rest-day for workers. Each individual date was also given a name (replacing the Catholic saints' days), with the quintidi and décadi being named after animals and agricultural tools respectively, and the remaining days after trees, bushes and plants. At the end of the year the five remaining days of the solar year (September 16th-22nd) were proclaimed holidays²: les Fêtes de la Vertu (Virtue), de la Génie (Talent), du Travail (Work), de l'Opinion (Opinion) and des Récompenses (Rewards). In leap years an additional Fête de la Révolution was celebrated.

The poet Fabre d'Églantine was given the task of naming Romme's months, choosing appelations intended to evoke the seasonal changes and the beauty of nature.

The new calendar was adopted by the National Convention on October 5th 1793 and all documents back-dated to regard the proclamation of the republic (September 21st, 1792) as the first day of Year I. Thus Sept 1792-Sept 1793 was Year I, 1793/4 was Year II, 1794/5 Year III etc. Ordinary people had difficulty adapting to the new calendar especially the ten-day week, which meant three more working days without a break, and threw the established conventions of trade such as markets and trade fairs into disarray. Nonetheless, it endured beyond the revolutionary period⁵, continuing to be used for several years after Napoleon took power. In 1801, while still First Consul, not yet Emperor, he negotiated a Concordat with Pope Pius VII which included among its terms that France was to return to the Gregorian Calendar. It is, however, debatable as to whether this or the system's widespread unpopularity or some other administrative motive was the real reason for the abolition of the radical new calendar, as the change-over did not take place until midnight of December 31, 1805 (10 Nivôse Year XIV), by which time Napoleon had annexed the Papal states, been excommunicated by Pius VII and consequently imprisoned him.