French Revolutionary Calendar
The Republican calendar year began the day the autumnal equinox occurred in Paris, and had twelve months of 30 days each, which were given new names based on nature, principally having to do with the prevailing weather in and around Paris.
Note: On many printed calendars of Year II (1793–94), the month of Thermidor was named Fervidor.
Each month had 30 days, and there were five intercalary (between month) holidays called "Sansculottides or six in a leap year.
The calendar was devised by Gilbert Romme (1750-1795) and the months were named by the poet Fabre d'Eglantine (1755-1794). It was adopted on 5 October 1793 (bizarrely, it was applied retrospectively from 22 September 1792) and continued in force until 1 January 1806, when Napoleon restored the Gregorian calendar.