In late 18th-century France, with the approach of the French Revolution, demands began to be made for a radical change in the civil calendar that would divorce it completely from any ecclesiastical connections. The first attacks on the Gregorian calendar and proposals for reform came in 1785 and 1788, the changes being primarily designed to divest the calendar of all its Christian associations. After the storming of the Bastille in July 1789, demands became more vociferous, and a new calendar, to start from "the first year of liberty," was widely spoken about. In 1793 the National Convention appointed Charles-Gilbert Romme, president of the committee of public instruction, to take charge of the reform. Technical matters were entrusted to the mathematicians Joseph-Louis Lagrange and Gaspard Monge and the renaming of the months to the Paris deputy to the convention, Philippe Fabre d'Églantine. The results of their deliberations were submitted to the convention in September of the same year and were immediately accepted, it being promulgated that the new calendar should become law on October 5. (See French Revolution.)

The French republican calendar, as the reformed system came to be known, was taken to have begun on September 22, 1792, the day of the proclamation of the Republic and, in that year, the date also of the autumnal equinox. The total number of days in the year was fixed at 365, the same as in the Julian and Gregorian calendars, and this was divided into 12 months of 30 days each, the remaining five days at year's end being devoted to festivals and vacations. These were to fall between September 17 and 22 and were specified, in order, to be festivals in honour of virtue, genius, labour, opinion, and rewards. In a leap year an extra festival was to be added--the festival of the Revolution. Leap years were retained at the same frequency as in the Gregorian calendar, but it was enacted that the first leap year should be year 3, not year 4 as it would have been if the Gregorian calendar had been followed precisely in this respect. Each four-year period was to be known as a Franciade.

The seven-day week was abandoned, and each 30-day month was divided into three periods of 10 days called décades, the last day of a décade being a rest day. It was also agreed that each day should be divided into decimal parts, but this was not popular in practice and was allowed to fall into disuse. [Note: since the week was divided into ten, the old seven-day names could not be used any more, so new 'day-names' were proposed: primidi, duodi, rdidi, quartidi, quintidi, sextidi, septidi, octidi, nonidi and décadi. (hs)]

The months themselves were renamed so that all previous associations should be lost, and Fabre d'Églantine chose descriptive names as follows (the descriptive nature and corresponding Gregorian calendar dates for years 1, 2, 3, 5, 6, and 7 are given in parentheses):
 

The French republican calendar was short-lived, for while it was satisfactory enough internally, it clearly made for difficulties in communication abroad because its months continually changed their relationship to dates in the Gregorian calendar. In September 1805, under the Napoleonic regime, the calendar was virtually abandoned, and on January 1, 1806, it was replaced by the Gregorian calendar.