The first Roman calendar appears to have been lunar, with ten months. According to tradition, in 509 bce the king Numa Pompilius replaced that calendar with one more like that of the Greeks: a year of 12 months and 355 days. Those months which had 30 days in the old calendar now had 29. Januarius (29 days), named after the god of gates, was added to the beginning of the year and Februarius (28 days), added to the end. In 450 bce, Januarius was moved from before Martius to before Februarius, which established the order of months we still use.
| Name of month | Derivation of Name | Number of days |
|---|---|---|
Martius |
from the god Mars | 31 |
Aprilis |
29 | |
Maius |
31 | |
Iunius |
from the goddess Juno, wife of Zeus | 29 |
Quintilis |
fifth | 31 |
Sextilis |
sixth | 29 |
September |
seventh | 29 |
October |
eighth | 31 |
November |
ninth | 29 |
December |
tenth | 29 |
Januarius |
from Janus, god of gates | 29 |
Februarius |
from Februa, a goddess of purification | 28 |
The year began on Martius 1, the day on which new consuls were inaugurated. In 154 bce a rebellion broke out in Spain. To avoid changing consuls in the middle of a war, New Year's was shifted up two months, to Januarius 1, beginning Januarius 1, 153 bce.
Since the total number of days in a year of months was less than a solar year, an extra month 22 or 23 days long, the mensis intercalaris, called Mercedonis, was added every two to four years after Februarius 23, followed by the last five days of Februarius. This addition had to be called for by the chief priest, the Pontifex Maximus. Our practice of adding the extra day for leap year in February, rather than December, is a survival of the Roman calendar.
The era of the later Roman calendar was that of the founding of the city, ab urbe condita (auc). In fact, the Romans introduced the concept of an era to Western calendars. The beginning of this era was placed by the Roman historian Marcus Terentius Varro (116–27 bce) at what we would call 753 bce.
The problem with the Roman calendar was that it was highly adjustable and the adjusters did not show any sense of astronomical discipline. Politicians, for example, sometimes succeeded in lengthening months to prevent their term of office from expiring at a critical point, or the chief priest failed to add the necessary mensis intercalaris at the right time. The result was that by the time Julius Caesar overthrew the Republic the calendar was three months out of whack with the seasons. See Julian calendar.
The Romans had a complicated way of stating what day of the month it was. It depended on three “milestone” days that occurred in every month:
|
Kalends |
the first day of the month (originally, the day of the new moon) |
|
Nones |
8 days before the Ides |
Ides |
the 15th day of Martius, Maius, Julius (originally Quintilis) and October; the 13th day of other months (originally, the Ides was the day of the full moon) |
To specify a date, the Romans counted backwards from the next of these “milestones.” So, for example, December 2 would be “ante diem IV nonae December.” Days after the Ides are given as days before the Kalends of the next month; that is, what we would call January 29 they called “3 days before the First of February.”
Another term encountered in the names of many days is “pridie,” which means “the day before.” Thus “pridie idus Martius” is the day before the ides of March.
This system was used in Europe as late as the 16th century.
The names of the days can be read from the following table. In writing, the names were usually abbreviated; the abbreviations are self-evident.
| Day of the month |
Month | ||||
|---|---|---|---|---|---|
|
Ianuarivs, Augustvs, December |
Februarivs (not a leap year) |
Februarivs (leap year) |
Martius, Maius, Iulius, October |
Aprilis, Iunius, September, November |
|
| 1 | kalendae M | kalendae M | kalendae M | kalendae M | kalendae M |
| 2 | ante diem IV nonae M |
ante diem IV nonae M |
ante diem IV nonae M |
ante diem VI nonae M |
ante diem IV nonae M |
| 3 | ante diem III nonae M |
ante diem III nonae M |
ante diem III nonae M |
ante diem V nonae M |
ante diem III nonae M |
| 4 | pridie nonae M |
pridie nonae M |
pridie nonae M |
ante diem IV nonae M |
pridie Nones |
| 5 | nonae M | nonae M | nonae M | ante diem III nonae M |
nonae M |
| 6 | ante diem VIII idus M |
ante diem VIII idus M |
ante diem VIII idus M |
pridie nonae M |
ante diem VIII idus M |
| 7 | ante diem VII idus M |
ante diem VII idus M |
ante diem VII idus M |
nonae M | ante diem VII idus M |
| 8 | ante diem VI idus M |
ante diem VI idus M |
ante diem VI idus M |
ante diem VIII idus M |
ante diem VI idus M |
| 9 | ante diem V idus M |
ante diem V idus M |
ante diem V idus M |
ante diem VII idus M |
ante diem V idus M |
| 10 | ante diem IV idus M |
ante diem IV idus M |
ante diem IV idus M |
ante diem VI idus M |
ante diem IV idus M |
| 11 | ante diem III idus M |
ante diem III idus M |
ante diem III idus M |
ante diem V idus M |
ante diem III idus M |
| 12 | pridie idus M |
pridie idus M |
pridie idus M |
ante diem IV idus M |
pridie idus M |
| 13 | idus M | idus M | idus M | ante diem III idus M |
idus M |
| 14 | ante diem XIX kalendae N |
ante diem XVI kalendae N |
ante diem XVI kalendae N |
pridie idus M |
ante diem XVIII kalendae N |
| 15 | ante diem XVIII kalendae N |
ante diem XV kalendae N |
ante diem XV kalendae N |
idus M | ante diem XVII kalandae N |
| 16 | ante diem XVII kalendae N |
ante diem XIV kalendae N |
ante diem XIV kalendae N |
ante diem XVII kalendae N |
ante diem XVI kalendae N |
| 17 | ante diem XVI kalendae N |
ante diem XIII kalendae N |
ante diem XIII kalendae N |
ante diem XVI kalendae N |
ante diem XV kalendae N |
| 18 | ante diem XV kalendae N |
ante diem XII kalendae N |
ante diem XII kalendae N |
ante diem XV kalendae N |
ante diem XIV kalendae N |
| 19 | ante diem XIV kalendae N |
ante diem XI kalendae N |
ante diem XI kalendae N |
ante diem XIV kalendae N |
ante diem XIII kalendae N |
| 20 | ante diem XIII kalendae N |
ante diem X kalendae N |
ante diem X kalendae N |
ante diem XIII kalendae N |
ante diem XII kalendae N |
| 21 | ante diem XII kalendae N |
ante diem IX kalendae N |
ante diem IX kalendae N |
ante diem XII kalendae N |
ante diem XI kalendae N |
| 22 | ante diem XI kalendae N |
ante diem VIII kalendae N |
ante diem VIII kalendae N |
ante diem XI kalendae N |
ante diem X kalendae N |
| 23 | ante diem X kalendae N |
ante diem VII kalendae N |
ante diem VII kalendae N |
ante diem X kalendae N |
ante diem IX kalendae N |
| 24 | ante diem IX kalendae N |
ante diem VI kalendae N |
ante diem VI kalendae N |
ante diem IX kalendae N |
ante diem VIII kalendae N |
| 25 | ante diem VIII kalendae N |
ante diem V kalendae N |
ante diem bis VI kalendae N |
ante diem VIII kalendae N |
ante diem VII kalendae N |
| 26 | ante diem VII kalendae N |
ante diem IV kalendae N |
ante diem V kalendae N |
ante diem VII kalendae N |
ante diem VI kalendae N |
| 27 | ante diem VI kalendae N |
ante diem III kalendae N |
ante diem IV kalendae N |
ante diem VI kalendae N |
ante diem V kalendae N |
| 28 | ante diem V kalendae N |
pridie kalendae N |
ante diem III kalendae N |
ante diem V kalendae N |
ante diem IV kalendae N |
| 29 | ante diem IV kalendae N |
— | pridie kalendae N |
ante diem IV kalendae N |
ante diem III kalendae N |
| 30 | ante diem III kalendae N |
— | — | ante diem III kalendae N |
pridie kalendae N |
| 31 | pridie kalendae N |
— | — | pridie kalendae N |
— |
Agnes Kirsopp Michels.
The Calendar of the Roman Republic.
Princeton, NJ: Princeton University Press, 1967.
Reprinted by the Greenwood Press (Westport, CT) in 1978.
Alan Edouard Samuel.
Greek and Roman Chronology: Calendars and Years in Classical Antiquity.
Munich: Beck, 1972.
From the series Handbuch der Altertumswissenschaft; 1 Abteilung, 7 T.
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