French Republican Calendar, series 1, 3/13. Pencil on paper. 2012. 29.5 cm x 41.5 cm. In 1792 the French revolutionary authorities introduced a new calendar, not just one stripped of Christian feast days and saints’ days, but an entirely new system of measuring time, the Calendrier Republicain, it lasted until the final day of 1805.

It was just one of a whole raft of reforms, including new educational institutions and new ways of measuring our material world; a new metric system of interrelated weights and measures.

The old seven-day week would be no more, each month would consist of three 10-day weeks. Most days would be named after crop plants, flowers or trees, other more special days after domesticated animals or agricultural implements. Despite being conceived by urban revolutionaries who violently imposed their will on their own rural populace, it was a calendar dedicated to the idealised countryside.

It was also a calendar dedicated to the sun, or rather the journey of the sun through the celestial sphere along the ecliptic; its 12 equal months were aligned with the zodiacal signs familiar to any horoscope reader. Its new year’s day was to be the autumn equinox, corrected as often as necessary by precise astronomical observation.

And so for a few years, the momentous events of the First Republic were marked out in this new purified calendar; the execution of Danton on 16 Germinal Year II, the arrest and execution of Robespierre on 9-19 Thermidor later that same year; Napoleon’s ‘whiff of grapeshot’ on 13 Vendemiaire Year IV, the coup of 18 Fructidor Year V and Napoleon’s assumption of supreme power on 18 Brumaire Year VIII.

Napoleon dismantled the Directory and with it the First Republic, initially as a Caesar-like Consul, then as an Emperor. Through him the post-revolutionary regime made its peace with the Catholic Church; the metric system survived but the new calendar was abandoned. The holy days and saints’ days returned after the concordat of 1801; the full Gregorian calendar returned with effect from 1 January 1806.