The ancient lunar Roman calendar underwent many changes before the reforms of
Julius Caesar which
went into effect in 45 B.C. and changed it to a solar calendar.
The Julian calendar consisted of the familiar twelve months and was 365 days in length.
The days of the months were not numbered sequentially as they are
now. Rather three set points in the month which, in the traditional
Roman calendar had originally corresponded to phases of the moon:
Kalends (new moon), Nones (first-quarter moon), and
Ides (full moon), were retained but reassigned --Kalends
to the first day of the month,
Ides to the middle of the month, corresponding to our 13th or 15th depending
on the month, and Nones to the day nine days before Ides--
without regard to the moon. The remaining
days of the month were denominated not, as in our system, by their relation to the
beginning of the month, but by their relation to the next of those three fixed
points /1/. For example, the Ides of March was the 15th;
the 14th of March would be
called PRIDIE ID. MAR., or "the day before the Ides of March."
To further complicate things,
the Romans counted inclusively, that is to say they counted the days between
now and the next fixed point, plus that fixed point. Thus, the 13th of
March was A. D. III ID. MAR., that is three days before the Ides
of March, counting the 13th, 14th, and the 15th. The Fourth of July in the
Roman calendar is A.D. IV NON. IUL., that is the fourth day before the
Nones of July (in July the Nones being on the 7th). For days of the month after
the Ides, the count looked forward to the Kalends of the following month.
Thus December 25, in Roman usage would be A.D. VIII KAL. IAN., or
eight days before the Kalends of January.
To keep the Julian calendar in sync with solar year of slightly less than
365-1/4 days, an extra day
was added every fourth year to the month of February.
Those bissextile /2/ years
are known, colloquially, as "leap" years. The Julian calendar slightly
over-adjusted for the difference between the true solar year and the 365-day
year, and over the centuries required another adjustment to the bissextile years
by Pope Gregory. The Gregorian calendar /3/
we now use retained the quadrennial bissextile year except in years evenly
divisible by 100, in which case
the year is bissextile only if it is also evenly divisible by 400.
JULIAN/GREGORIAN CALENDAR
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MENSIS IANUARIUS
Kalendae Ianuariae
a.d.IV.Non.Ian
a.d.III.Non.Ian.
pridie Non.Ian.
Nonae Ianuariae
a.d.VIII.Id.Ian.
a.d.VII. Id.Ian.
a.d.VI. Id.Ian.
a.d.V. Id.Ian.
a.d.IV. Id.Ian.
a.d.III. Id.Ian.
pridie Id.Ian.
Idus Ianuariae
a.d.XIX.Kal.Feb.
a.d.XVIII.Kal.Feb.
a.d.XVII.Kal.Feb.
a.d.XVI.Kal.Feb.
a.d.XV.Kal.Feb.
a.d.XIV.Kal.Feb.
a.d.XIII.Kal.Feb.
a.d.XII.Kal.Feb.
a.d.XI.Kal.Feb.
a.d.X.Kal.Feb.
a.d.IX.Kal.Feb.
a.d.VIII.Kal.Feb.
a.d.VII.Kal.Feb.
a.d.VI.Kal.Feb.
a.d.V.Kal.Feb.
a.d.IV.Kal.Feb.
a.d.III.Kal.Feb.
pridie Kal.Feb.
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MENSIS FEBRUARIUS
Kalendae Februariae
a.d.IV.Non.Feb.
a.d.III.Non.Feb.
pridie Non. Feb.
Nonae Februariae
a.d.VIII.Id.Feb.
a.d.VII.Id.Feb.
a.d.VI.Id.Feb
a.d.V.Id.Feb.
a.d.IV.Id.Feb.
a.d.III.Id.Feb.
pridie Id. Feb.
Idus Februariae
a.d.XVI.Kal.Mar.
a.d.XV.Kal.Mar. Lupercalia
a.d.XIV.Kal.Mar.
a.d.XIII.Kal.Mar.
a.d.XII.Kal.Mar.
a.d.XI.Kal.Mar.
a.d.X.Kal.Mar.
a.d.IX.Kal.Mar.
a.d.VIII.Kal.Mar.
a.d.VII.Kal.Mar. Terminalia
a.d.VI.Kal.Mar.
a.d.V.Kal.Mar.
a.d.IV.Kal.Mar.
a.d.III.Kal.Mar.
pridie Kal.Mar.
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MENSIS MARTIUS
Kalendae Martiae
a.d.VI.Non.Mar.
a.d.V.Non.Mar.
a.d.IV.Non.Mar.
a.d.III.Non.Mar.
pridie Non.Mar.
Nonae Martiae
a.d.VIII.Id.Mar.
a.d.VII.Id.Mar.
a.d.VI.Id.Mar.
a.d.V.Id.Mar.
a.d.IV.Id.Mar.
a.d.III.Id.Mar.
pridie Id.Mar.
Idus Martiae
a.d.XVII.Kal.Apr.
a.d.XVI.Kal.Apr.
a.d.XV.Kal.Apr.
a.d.XIV.Kal.Apr.
a.d.XIII.Kal.Apr.
a.d.XII.Kal.Apr.
a.d.XI.Kal.Apr.
a.d.X.Kal.Apr.
a.d.IX.Kal.Apr.
a.d.VIII.Kal.Apr.
a.d.VII.Kal.Apr.
a.d.VI.Kal.Apr.
a.d.V.Kal.Apr.
a.d.IV.Kal.Apr.
a.d.III.Kal.Apr.
pridie Kal.Apr.
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MENSIS APRILIS
Kalendae Apriles
a.d.IV.Non.Apr.
a.d.III.Non.Apr.
pridie Non.Apr.
Nonae Apriles
a.d.VIII.Id.Apr.
a.d.VII.Id.Apr.
a.d.VI.Id.Apr.
a.d.V.Id.Apr.
a.d.IV.Id.Apr.
a.d.III.Id.Apr.
pridie Id.Apr.
Idus Apriles
a.d.XVIII.Kal.Mai.
a.d.XVII.Kal.Mai.
a.d.XVI.Kal.Mai.
a.d.XV.Kal.Mai.
a.d.XIV.Kal.Mai.
a.d.XIII.Kal.Mai.
a.d.XII.Kal.Mai.
a.d.XI.Kal.Mai. Parilia (The birthday of Rome)
a.d.X.Kal.Mai.
a.d.IX.Kal.Mai.
a.d.VIII.Kal.Mai.
a.d.VII.Kal.Mai. Robigalia
a.d.VI.Kal.Mai.
a.d.V.Kal.Mai.
a.d.IV.Kal.Mai. Floralia
a.d.III.Kal.Mai.
pridie Kal.Mai.
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MENSIS MAIUS
Kalendae Maiae
a.d.VI.Non.Mai.
a.d.V.Non.Mai.
a.d.IV.Non.Mai.
a.d.III.Non.Mai.
pridie Non.Mai.
Nonae Maiae
a.d.VIII.Id.Mai.
a.d.VII.Id.Mai.
a.d.VI.Id.Mai.
a.d.V.Id.Mai.
a.d.IV.Id.Mai.
a.d.III.Id.Mai.
pridie Id.Mai.
Idus Maiae
a.d.XVII.Kal.Iun.
a.d.XVI.Kal.Iun.
a.d.XV.Kal.Iun.
a.d.XIV.Kal.Iun.
a.d.XIII.Kal.Iun.
a.d.XII.Kal.Iun.
a.d.XI.Kal.Iun.
a.d.X.Kal.Iun.
a.d.IX.Kal.Iun.
a.d.VIII.Kal.Iun.
a.d.VII.Kal.Iun.
a.d.VI.Kal.Iun.
a.d.V.Kal.Iun.
a.d.IV.Kal.Iun.
a.d.III.Kal.Iun.
pridie Kal.Iun.
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MENSIS IUNIUS
Kalendae Iuniae
a.d.IV.Non.Iun.
a.d.III.Non.Iun.
pridie Non.Iun.
Nonae Juniae
a.d.VIII.Id.Iun.
a.d.VII.Id.Iun.
a.d.VI.Id.Iun.
a.d.V.Id.Iun.
a.d.IV.Id.Iun.
a.d.III.Id.Iun.
pridie Id.Iun.
Idus Iuniae
a.d.XVIII.Kal.Iul.
a.d.XVII.Kal.Iul.
a.d.XVI.Kal.Iul.
a.d.XV.Kal.Iul.
a.d.XIV.Kal.Iul.
a.d.XIII.Kal.Iul.
a.d.XII.Kal.Iul.
a.d.XI.Kal.Iul.
a.d.X.Kal.Iul.
a.d.IX.Kal.Iul.
a.d.VIII.Kal.Iul.
a.d.VII.Kal.Iul.
a.d.VI.Kal.Iul.
a.d.V.Kal.Iul.
a.d.IV.Kal.Iul.
a.d.III.Kal.Iul.
pridie Kal.Iul.
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MENSIS IULIUS (Quinctilis)
Kalendae Iuliae
a.d.VI.Non.Iul.
a.d.V.Non.Iul.
a.d.IV.Non.Iul.
a.d.III.Non.Iul.
pridie Non.Iul.
Nonae Juliae
a.d.VIII.Id.Iul.
a.d.VII.Id.Iul.
a.d.VI.Id.Iul.
a.d.V.Id.Iul.
a.d.IV.Id.Iul.
a.d.III.Id.Iul.
pridie Id.Iul.
Idus Iuliae
a.d.XVII.Kal.Aug.
a.d.XVI.Kal.Aug.
a.d.XV.Kal.Aug.
a.d.XIV.Kal.Aug.
a.d.XIII.Kal.Aug.
a.d.XII.Kal.Aug.
a.d.XI.Kal.Aug.
a.d.X.Kal.Aug.
a.d.IX.Kal.Aug.
a.d.VIII.Kal.Aug.
a.d.VII.Kal.Aug.
a.d.VI.Kal.Aug.
a.d.V.Kal.Aug.
a.d.IV.Kal.Aug.
a.d.III.Kal.Aug.
pridie Kal.Aug.
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MENSIS AUGUSTUS (Sextilis)
Kalendae Augustae
a.d.IV.Non.Aug.
a.d.III.Non.Aug.
pridie Non.Aug.
Nonae Augustae
a.d.VIII.Id.Aug.
a.d.VII.Id.Aug.
a.d.VI.Id.Aug.
a.d.V.Id.Aug.
a.d.IV.Id.Aug.
a.d.III.Id.Aug.
pridie Id.Aug.
Idus Augustae
a.d.XIX.Kal.Sept.
a.d.XVIII.Kal.Sept.
a.d.XVII.Kal.Sept.
a.d.XVI.Kal.Sept.
a.d.XV.Kal.Sept.
a.d.XIV.Kal.Sept.
a.d.XIII.Kal.Sept.
a.d.XII.Kal.Sept.
a.d.XI.Kal.Sept.
a.d.X.Kal.Sept.
a.d.IX.Kal.Sept.
a.d.VIII.Kal.Sept.
a.d.VII.Kal.Sept.
a.d.VI.Kal.Sept.
a.d.V.Kal.Sept.
a.d.IV.Kal.Sept.
a.d.III.Kal.Sept.
pridie Kal.Sept.
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MENSIS SEPTEMBER
Kalendae Septembres
a.d.IV.Non.Sept.
a.d.III.Non.Sept.
pridie Non.Sept.
Nonae Septembres
a.d.VIII.Id.Sept.
a.d.VII.Id.Sept.
a.d.VI.Id.Sept.
a.d.V.Id.Sept.
a.d.IV.Id.Sept.
a.d.III.Id.Sept.
pridie Id.Sept.
Idus Septembres
a.d.XVIII.Kal.Oct.
a.d.XVII.Kal.Oct.
a.d.XVI.Kal.Oct.
a.d.XV.Kal.Oct.
a.d.XIV.Kal.Oct.
a.d.XIII.Kal.Oct.
a.d.XII.Kal.Oct.
a.d.XI.Kal.Oct
a.d.X.Kal.Oct.
a.d.IX.Kal.Oct.
a.d.VIII.Kal.Oct.
a.d.VII.Kal.Oct.
a.d.VI.Kal.Oct.
a.d.V.Kal.Oct.
a.d.IV.Kal.Oct.
a.d.III.Kal.Oct.
pridie Kal.Oct.
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MENSIS OCTOBER
Kalendae Octobres
a.d.VI.Non.Oct.
a.d.V.Non.Oct.
a.d.IV.Non.Oct.
a.d.III.Non.Oct.
pridie Non.Oct.
Nonae Octobres
a.d.VIII.Id.Oct.
a.d.VII.Id.Oct.
a.d.VI.Id.Oct.
a.d.V.Id.Oct.
a.d.IV.Id.Oct.
a.d.III.Id.Oct.
pridie Id.Oct.
Idus Octobres
a.d.XVII.Kal.Nov.
a.d.XVI.Kal.Nov.
a.d.XV.Kal.Nov.
a.d.XIV.Kal.Nov.
a.d.XIII.Kal.Nov.
a.d.XII.Kal.Nov.
a.d.XI.Kal.Nov.
a.d.X.Kal.Nov.
a.d.IX.Kal.Nov.
a.d.VIII.Kal.Nov.
a.d.VII.Kal.Nov.
a.d.VI.Kal.Nov.
a.d.V.Kal.Nov.
a.d.IV.Kal.Nov.
a.d.III.Kal.Nov.
pridie Kal.Nov.
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MENSIS NOVEMBER
Kalendae Novembres
a.d.IV.Non.Nov.
a.d.III.Non.Nov.
pridie Non.Nov.
Nonae Novembres
a.d.VIII.Id.Nov.
a.d.VII.Id.Nov.
a.d.VI.Id.Nov.
a.d.V.Id.Nov.
a.d.IV.Id.Nov.
a.d.III.Id.Nov.
pridie Id.Nov.
Idus Novembres
a.d.XVIII.Kal.Dec.
a.d.XVII.Kal.Dec.
a.d.XVI.Kal.Dec.
a.d.XV.Kal.Dec.
a.d.XIV.Kal.Dec.
a.d.XIII.Kal.Dec.
a.d.XII.Kal.Dec.
a.d.XI.Kal.Dec.
a.d.X.Kal.Dec.
a.d.IX.Kal.Dec.
a.d.VIII.Kal.Dec.
a.d.VII.Kal.Dec.
a.d.VI.Kal.Dec.
a.d.V.Kal.Dec.
a.d.IV.Kal.Dec.
a.d.III.Kal.Dec.
pridie Kal.Dec.
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MENSIS DECEMBER
Kalendae Decembres
a.d.IV.Non.Dec.
a.d.III.Non.Dec.
pridie Non.Dec.
Nonae Decembres
a.d.VIII.Id.Dec.
a.d.VII.Id.Dec.
a.d.VI.Id.Dec.
a.d.V.Id.Dec.
a.d.IV.Id.Dec.
a.d.III.Id.Dec.
pridie Id.Dec.
Idus Decembres
a.d.XIX.Kal.Ian.
a.d.XVIII.Kal.Ian.
a.d.XVII.Kal.Ian.
a.d.XVI.Kal.Ian Saturnalia
a.d.XV.Kal.Ian.
a.d.XIV.Kal.Ian.
a.d.XIII.Kal.Ian.
a.d.XII.Kal.Ian.
a.d.XI.Kal.Ian.
a.d.X.Kal.Ian.
a.d.IX.Kal.Ian.
a.d.VIII.Kal.Ian.
a.d.VII.Kal.Ian.
a.d.VI.Kal.Ian.
a.d.V.Kal.Ian.
a.d.IV.Kal.Ian.
a.d.III.Kal.Ian.
pridie Kal.Ian.
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NOTES
/1/ The adoption of the current custom of numbering
the days of the month sequentially, and the attendant disuse of the old system of designating
the days by their relation to Kalends, Nones, and Ides, came about
gradually. In England, for example, both the First Prayerbook of Edward VI (1549)
and the Second Prayerbook of Edward VI (1552) as well as the Authorized Version of the Scriptures
(1611) contain calendars that use both systems side-by-side. Viewers of Shakespeare's play
Julius Caesar (ca. 1599) would have been quite at home with his references to the
Ides of March.
/2/ Our calendars which number the
days of the month sequentially from the first day
of the month result in a 29th day added to the end of February in the "leap" year, however
this is not strictly correct. The "leap" day is in fact, added before the 24th. The 24th
day of February is in roman usage ante diem sextum calendas martii (A.D. VI KAL. MAR.),
the sixth day before the Kalends of March, every fourth year the Julian calendar adds
a second February 24, or bis, meaning twice, sextum, meaning sixth,
day before March. In a bissextile year, the calendar for February looks like this:
MENSIS FEBRUARIUS
Kalendae Februariae
a.d.IV.Non.Feb.
a.d.III.Non.Feb.
pridie Non. Feb.
Nonae Februariae
a.d.VIII.Id.Feb.
a.d.VII.Id.Feb.
a.d.VI.Id.Feb
a.d.V.Id.Feb.
a.d.IV.Id.Feb.
a.d.III.Id.Feb.
pridie Id. Feb.
Idus Februariae
a.d.XVI.Kal.Mar.
a.d.XV.Kal.Mar. Lupercalia
a.d.XIV.Kal.Mar.
a.d.XIII.Kal.Mar.
a.d.XII.Kal.Mar.
a.d.XI.Kal.Mar.
a.d.X.Kal.Mar.
a.d.IX.Kal.Mar.
a.d.VIII.Kal.Mar.
a.d.VII.Kal.Mar. Terminalia
Bis a.d.VI.Kal.Mar.
a.d.VI.Kal.Mar.
a.d.V.Kal.Mar.
a.d.IV.Kal.Mar.
a.d.III.Kal.Mar.
pridie Kal.Mar.
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/3/ By the time Catholic Europe
switched to the Gregorian Calendar in 1582, the Julian Calendar
was off by ten days; when Great Britain adopted the Gregorian Calendar in 1752
the difference was 11 days. The last Europe nation to make the switch was Greece, in 1923.
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