This article is from the Calendars FAQ, by Claus Tondering firstname.lastname@example.org with numerous contributions by others.
Leap years were introduced to keep New Year's Day on autumnal
equinox. But this turned out to be difficult to handle, because
equinox is not completely simple to predict.
In fact, the first decree implementing the calendar (5 Oct 1793)
contained two contradictory rules, as it stated that:
- the first day of each year would be that of the autumnal equinox
- every 4th year would be a leap year
In practice, the first calendars were based on the equinoxial
To remove the confusion, a rule similar to the one used in the
Gregorian Calendar (including a 4000 year rule as described in section
2.2.2) was proposed by the calendar's author, Charles Rommes, but his
proposal ran into political problems.
In short, during the time when the French Revolutionary Calendar was
in use, the following years were leap years: 3, 7, and 11.