previous page: 2.6. When can I reuse my 1992 calendar?
page up: Calendars FAQ
next page: 2.7.1. How did the Romans number days?

2.7. What is the Roman calendar?


This article is from the Calendars FAQ, by Claus Tondering claus@tondering.dk with numerous contributions by others.

2.7. What is the Roman calendar?

Before Julius Caesar introduced the Julian calendar in 45 BC, the
Roman calendar was a mess, and much of our so-called "knowledge" about
it seems to be little more than guesswork.

Originally, the year started on 1 March and consisted of only 304 days
or 10 months (Martius, Aprilis, Maius, Junius, Quintilis, Sextilis,
September, October, November, and December). These 304 days were
followed by an unnamed and unnumbered winter period. The Roman king
Numa Pompilius (c. 715-673 BC, although his historicity is disputed)
allegedly introduced February and January (in that order) between
December and March, increasing the length of the year to 354 or 355
days. In 450 BC, February was moved to its current position between
January and March.

In order to make up for the lack of days in a year, an extra month,
Intercalaris or Mercedonius, (allegedly with 22 or 23 days though some
authorities dispute this) was introduced in some years. In an 8 year
period the length of the years were:
1: 12 months or 355 days
2: 13 months or 377 days
3: 12 months or 355 days
4: 13 months or 378 days
5: 12 months or 355 days
6: 13 months or 377 days
7: 12 months or 355 days
8: 13 months or 378 days
A total of 2930 days corresponding to a year of 366 1/4 days. This
year was discovered to be too long, and therefore 7 days were later
dropped from the 8th year, yielding 365.375 days per year.

This is all theory. In practice it was the duty of the priesthood to
keep track of the calendars, but they failed miserably, partly due to
ignorance, partly because they were bribed to make certain years long
and other years short. Furthermore, leap years were considered unlucky
and were therefore avoided in time of crisis, such as the Second Punic

In order to clean up this mess, Julius Caesar made his famous calendar
reform in 45 BC. We can make an educated guess about the length of the
months in the years 47 and 46 BC:

                47 BC          46 BC
January          29             29
February         28             24
Intercalaris                    27
March            31             31
April            29             29
May              31             31
June             29             29
Quintilis        31             31
Sextilis         29             29
September        29             29
October          31             31
November         29             29
Undecember                      33
Duodecember                     34
December         29             29
                ---            ---
Total           355            445

The length of the months from 45 BC onward were the same as the ones
we know today.

Occasionally one reads the following story:
"Julius Caesar made all odd numbered months 31 days long, and
all even numbered months 30 days long (with February having 29
days in non-leap years). In 44 BC Quintilis was renamed
'Julius' (July) in honour of Julius Caesar, and in 8 BC
Sextilis became 'Augustus' in honour of emperor Augustus. When
Augustus had a month named after him, he wanted his month to
be a full 31 days long, so he removed a day from February and
shifted the length of the other months so that August would
have 31 days."
This story, however, has no basis in actual fact. It is a fabrication
possibly dating back to the 14th century.


Continue to:

previous page: 2.6. When can I reuse my 1992 calendar?
page up: Calendars FAQ
next page: 2.7.1. How did the Romans number days?