The Republican calendar was instituted during the French Revolution by the National Convention on 24 October 1793, to replace the Gregorian calendar. Like the metric system, the Republican calendar set out to reform society, including even its references to time and space. To counter superstition and fanaticism, Sunday, saints and Christian feast days were abolished in the name of Reason, science, nature, poetry, ideology and utopia. This calendar was used in France from 1793 to 1806. The year begins with the autumn equinox (22 or 23 September). It is divided into 12 months of 30 days, in turn divided into three periods of 10 days, known as "decades". Each day was named according to its numeral in the number system: primidi, duodi, tridi, quartidi, quintidi, sextidi, septidi, octidi, nonidi, dÈcadi. The last day of each "decade" corresponded to a day of rest. The five or six "complementary" days remaining at the end of the year (from 17 to 21 September approximately) were devoted to the celebration of Republican festivities. The first year of the new system was called Year I, the second Year II, and so forth. Each season comprised three months; the autumn months were named vendÈmiaire ("month of the Grape Harvest"), brumaire ("month of the Mists") and frimaire ("month of Wintry Weather"); the winter months, nivÙse ("month of the Snows"), pluviÙse ("month of the Rains") and ventÙse ("month of the Winds"); the spring months, germinal ("month of Germination"), florÈal ("month of Flowers") and prairial ("month of the Meadows"); and the summer months, messidor ("month of the Harvest"), thermidor ("month of Summer Heat") and fructidor ("month of Fruits"). The Republican calendar was abolished by Napoleon I on 1 January 1806. The Revolutionary calendar was phased in: following the abolition of the monarchy, 2 September 1792 was decreed by the Convention as Year I of the Republic and was henceforth to be the system used to date all documents. It is worth noting that this date coincides with the autumn equinox. The Convention decreed on 2 January 1793 that Year II of the Republic began on 1 January. On 5 October 1793, it was decided to count the years from 22 September. This decree was retroactive for the period from 1 January to 21 September 1793. This same decree established the Revolutionary calendar. A committee comprising Fabre d'Eglantine, David, Chenier and Romme was tasked on 18 October with devising the new calendar. This calendar was adopted on 3 brumaire an II (24 October) and promulgated on 4 frimaire (24 November). The year begins on the day of the autumn solstice (between 22 and 24 September) and consists of 12 months of 30 days each. The 5 or 6 additional days needed to reach the autumn solstice are referred to as complementary days. The names of each month were chosen by Fabre d'Eglantine and represent the seasons:adding the suffix "aire" for autumn (VendÈmiaire, Brumaire, Frimaire); "Ùse" for winter (NivÙse, PluviÙse, VentÙse); "al" for spring (Germinal, FlorÈal, Prairial); and "idor" for summer (Messidor, Thermidor (originally Fervidor), Fructidor). Each month is split into 3 "decades" of 10 days each, called:Primidi (or primdi, primedi) Duodi Tridi Quartidi Quintidi Sextidi Septidi Octidi Nonidi Decadi. The complementary days were known as "sans-culottides" and were later (on 7 fructidor III) named: Fête de la Vertu (Celebration of Virtue) Fête de Génie (Celebration of Talent) Fête du Travail (Celebration of Labour) Fête de l'Opinion (Celebration of Convictions) Fête des Récompenses (Celebration of Honours). This calendar would be abandoned for all but official documents by the end of the Revolution. The Gregorian calendar replaced it on 1 January 1806. The Commune of 1871 alone used it to date certain documents (Year 79). Difficulties of conversion. The principle behind this calendar is very simple but the dates suggested in some correspondence tables or genealogy programmes are mismatched by 1 or 2 days. Possible confusion: The year does not begin on 22 September (anniversary of the Republic) but on the day of the autumn solstice (22 to 24). The year 1800 (Year VIII) is not a leap year because it is divisible by 100 but not by 400.