A Brief History of the Calendar

by David Harper, PhD, FRAS

The Age of Reason

The Gregorian calendar, aside from its rules for determining Easter, is hardly more complicated than the Julian calendar which it replaced. The regular procession of leap-years is interrupted only three times in four hundred years. Almost two centuries can elapse (from 1901 to 2099, for example) during which the Julian leap-year rule applies. And yet the Gregorian calendar will keep step with the seasons for three thousand years before a day's correction is needed again.

In the aftermath of the French Revolution, such considerations were secondary to the zeal to throw off everything which reminded the citoyens of the yoke of monarchy and the church. Thus the Gregorian calendar was replaced by one which paid no allegiance to religion. It was designed by astronomers and mathematicians and was held up as a product of the new Age of Reason.

It harked back to the calendar of ancient Egypt. It had twelve equal months of thirty days, plus five or six festive days at the end of the year. Each month was divided into three ten-day weeks or decades.

The months were given names to reflect Nature and the changing seasons. They had a certain poetry.

Order Name Gregorian dates¹ Meaning of name Origin of name
1st Vendémiaire 22 Sept - 21 Oct Grape harvest Latin: vindemia
2nd Brumaire 22 Oct - 20 Nov Mist and fog French: brume
3rd Frimaire 21 Nov - 20 Dec Wintry weather French: frimas
4th Nivôse 21 Dec - 19 Jan Snowy Latin: nivosus
5th Pluviôse 20 Jan - 18 Feb Rainy Latin: pluviosus
6th Ventôse 19 Feb - 20 Mar² Windy Latin: ventosus
7th Germinal 21 Mar - 19 Apr Germination Latin: germen, germinis
8th Floréal 20 Apr - 19 May Flowering Latin: floreus
9th Prairial 20 May - 18 June Meadow French: prairie
10th Messidor 19 June - 18 July Harvest Latin: messis + Greek: dôron (gift)
11th Thermidor 19 July - 17 Aug Summer heat Greek: thermon + dôron
12th Fructidor 18 Aug - 16 Sept Fruitfulness Latin: fructus + Greek: dôron

¹ These dates are correct for Year 2 of the Republican calendar. The Republican year can also begin on 23 or 24 September.
² Dates will shift by one day after 28 February in a Gregorian leap year.

The five days at the end of the year were dedicated to the sans-culottes, the impoverished citizens who manned the barricades despite being under-dressed. The days were named after Virtue, Genius, Labour, Opinion and Recompense. In leap-years, the sixth day celebrated the French Republic itself.

The New Year was to begin on the date of the Autumn Equinox. The new calendar began on September 22nd, 1792.

The French Republican calendar faced several difficulties. The first, and greatest, was that nobody outside France recognised it, so that the French were forced to put two dates - one Republican, one Gregorian - on any letter or document that was to be sent outside France.

The second arose when the citoyens realised that in place of 52 days of rest each year, the new calendar gave them only 36.

The third was the rule which governed the New Year. To conform to truly scientific principles, and to reject all historical and religious precedents, it had been decided that New Year's Day each year should be the day on which the Autumn Equinox fell, on the meridian of Paris.

The problem is that the exact instant of the Equinox varies from year to year by up to 20 minutes either side of the mean instant that is predicted by the length of the tropical year. The variation arises from a combination of the nutation or "nodding" of the Earth's axis of rotation and the small deviations or perturbations of the position of the Earth in its orbit around the Sun due to the gravitational attraction of the other planet and the Moon.

In order to predict the amount by which the Equinox is slow or fast, astronomers can construct complicated mathematical formulae for the perturbations and the nutation with the aid of computers. In 18th-century France, such calculations had to be done by hand, and this was very laborious and time-consuming. It was not a good way to design a calendar.

In England, the Republican calendar met with derision. There was even a parody of the names of the months:

Autumn: Wheezy, Sneezy, Freezy
Winter: Slippy, Drippy, Nippy
Spring: Showery, Bowery, Flowery
Summer: Hoppy, Croppy, Poppy

France's Republican Calendar, the calendar of the Age of Reason, survived almost thirteen years. In 1806, Napoleon Bonaparte ordered that France should return to the Gregorian calendar.


I wish to thank Marco Faustinelli for pointing out errors in the original version of this chapter, and Dana Stockman for providing detailed etymologies of the names of the months of the Republican calendar.