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The Roman calendar changed its form several times between the founding of Rome and the fall of the Roman Empire. This article generally discusses the early Roman or 'pre-Julian' calendars. The calendar used after 46 BC is discussed under Julian calendar.

Fasti Antiates Maiores—Painting of the Roman calendar about 60 BC, before the Julian reform. Observe (enlarged) that it contains the months Quintilis ("QVI") and Sextilis ("SEX"), and displays the intercalary month ("INTER") as the far righthand column.

History[link]

The original Roman calendar is believed to have been a lunar calendar,^[1] which may have been based on one of the Greek lunar calendars. As the time between new moons averages 29.5 days, its months were constructed to be either hollow (29 days) or full (30 days). Full months were considered powerful and therefore auspicious; hollow months were unlucky. Unlike currently used dates, which are numbered sequentially from the beginning of the month, the Romans counted backwards from three fixed points: the Nones, the Ides and the Kalends of the following month. This system originated in the practice of "calling" the new month when the lunar crescent was first observed in the west after sunset. From the shape and orientation of the new moon, the number of days remaining to the nones would be proclaimed. At some point of history dates of months ceased to be connected with lunar phases, but it is unknown when it happened.

Calendar of Romulus[link]

Roman writers claimed that their calendar was invented by Romulus, the founder of Rome around 753 BC. His version contained ten months with the vernal equinox in the first month:

The calendar year lasted for 304 days. An additional number of winter days, reckoned between the end of December and the beginning of the following March, were not assigned to any month.^[3]

The later months were named based on their position in the calendar: Quintilis comes from quinque (meaning five), Sextilis from sex (meaning six), September from septem (meaning seven), October from octo (meaning eight), November from novem (meaning nine) and December from decem (meaning ten).

Calendar of Numa[link]

Numa Pompilius, the second of the seven traditional kings of Rome, reformed the calendar of Romulus by prefixing January and February around 713 BC to the original ten months; thus the names of Quintilis, Sextilis, September, October, November and December (implying fifth through tenth) no longer agreed with their position in his calendar.

Although Numa wanted to have a lunar year of 354 days, Romans considered odd numbers to be lucky,^[4] so Numa added 51 days to the 304 days in the calendar of Romulus and took one day from each of the six 30-day months giving a total of 57 days to share between January and February. January was given 29 days leaving February with the unlucky number of 28 days, suitable for the month of purification. Of the eleven months with an odd number of days, four had 31 days each and seven had 29 days each.

February was split into two parts, each with an odd number of days. The first part ended with the Terminalia on the 23rd, which was considered the end of the religious year; the five remaining days formed the second part. In order to keep the calendar year roughly aligned with the solar year, a leap month (the Mensis Intercalaris, sometimes also known as Mercedonius or Mercedinus), was added from time to time between the two parts of February. This caused the second part of February to be incorporated in the intercalary month as its last five days; there was thus no change either in their dates or the festivals observed on them. The resulting leap year was either 377 or 378 days long, depending on whether Intercalaris began on the day after the Terminalia^[8] or the second day after the Terminalia.^[9] Intercalaris had 27 days, its nones were on the fifth and its ides on the thirteenth as usual; the next following day was a.d. XV Kal. Mart.^[10]

The decision to insert the intercalary month was the responsibility of the pontifex maximus. On average, this happened roughly in alternate years. The system of aligning the year through intercalary months broke down at least twice: the first time was during and after the Second Punic War. It led to the reform of the Lex Acilia in 191 BC, the details of which are unclear, but it appears to have successfully regulated intercalation for over a century. The second breakdown was in the middle of the 1st century BC and may have been related to the increasingly chaotic and adversarial nature of Roman politics at the time. The position of pontifex maximus was not a full-time job; it was held by a member of the Roman elite, who would almost invariably be involved in the machinations of Roman politics. Because a Roman calendar year defined the term of office of elected Roman magistrates, a pontifex maximus would have reason to lengthen a year in which he or his allies were in power, or shorten a year in which his political opponents held office. It was while Julius Caesar was pontifex maximus that the calendar was overhauled, with the result being the Julian calendar. The calendar reforms were completed during the reign of his successor Augustus. Quintilis was renamed Iulius (July) in honour of Julius Caesar in 44 BC and Sextilis was renamed Augustus (August) in honour of Augustus in 8 BC.

Months[link]

In the earliest times the three reference dates were probably declared publicly, when appropriate lunar conditions were observed. After the reforms of Numa, they occurred on fixed days.

• Kalendae (whence "calendar"), Kalends—first day of the month; it is thought to have originally been the day of the new moon. The word is from the Greek καλέω, i.e. announce (the sighting of the new moon).
• Nonae, Nones—thought to have originally been the day of the half moon. The Nones was eight days before the Ides, and fell on the 5th or 7th day of the month, depending on the position of the Ides. (Nones implies ninth because, counting Ides as first, one day before is the second, and eight days before is the ninth).
• Idus, Ides—thought to have originally been the day of the full moon, was the 13th day of most months, but the 15th day of March, May, July, and October.

The day preceding the Kalends, Nones, or Ides was Pridie, e.g. Prid. Id. Mart. = 14 March. Other days were denoted by ordinal number, counting back from a named reference day. The reference day itself counted as the first, so that two days before was denoted the third day. Dates were written as a.d. NN, an abbreviation for ante diem NN, meaning "on the Nth (Numerus) day before the named reference day (Nomen)",^[11] e.g. a.d. III Kal. Nov. = on the third day before the November Kalends = 30 October. The value 2 was not used to denote a day before the fixed point, because second was the same as pridie. Further examples of date equivalence are: a.d. IV Non. Jan. = 2 January; a.d. VI Non. Mai. = 2 May; a.d. VIII Id. Apr. = 6 April; a.d. VIII Id. Oct. = 8 October; a.d. XVII Kal. Nov. = 16 October.

Some dates were sometimes known by the name of a festival that occurred on them, or shortly afterwards. Examples of such dates are recorded for the Feralia, Quirinalia and the Terminalia (though not yet for the Lupercalia). These dates are all after the Ides of February, which suggests that they are connected with resolving an ambiguity that could arise in intercalary years: dates of the form a.d. [N] Kal. Mart. were dates in late February in regular years but were a month later in intercalary years. However, it is much debated whether there was a fixed rule for using festival-based dates. It has been variously proposed that a date like a.d. X Terminalia (known from an inscription in 94 BC) implied that its year was, was not, or might have been intercalary.

When Julius Caesar added days to some months, he added them to the end of the month, so as not to disturb the dates of festivals in those months. This increased the count of all days after the Ides, and had some odd effects. For example, the emperor Augustus was born in 63 BC on the 23rd day of September. In the pre-Julian calendar this is seven days before the Kalends of October (or, in Roman style, counting inclusively, a.d. VIII Kal. Oct.), but in the Julian calendar it is eight days (a.d. IX Kal. Oct.). Because of this ambiguity, his birthday was sometimes celebrated on both dates.

Nundinal cycle[link]

The Romans of the Republic, like the Etruscans, used a "market week" of eight days, marked as A to H in the calendar. A nundina was the market day; etymologically, the word is related to novem, "nine," because the Roman system of counting was inclusive. The market "week" is the nundinal cycle. Since the length of the year was not a multiple of eight days, the letter for the market day (known as a "nundinal letter") changed every year. For example, if the letter for market days in some year was A and the year was 355 days long, then the letter for the next year would be F.

The nundinal cycle formed one rhythm of day-to-day Roman life; the market day was the day that country people would come to the city, and the day that city people would buy their eight days' worth of groceries. For this reason, a law was passed in 287 BC (the Lex Hortensia) that forbade the holding of meetings of the comitia (for example to hold elections) on market days, but permitted the holding of legal actions. In the late republic, a superstition arose that it was unlucky to start the year with a market day (i.e. for the market day to fall on 1 January, with a letter A), and the pontiffs, who regulated the calendar, took steps to avoid it.

Because the nundinal cycle was absolutely fixed at eight days under the Republic, information about the dates of market days is one of the most important tools we have for working out the Julian equivalent of a Roman date in the pre-Julian calendar. In the early Empire, the Roman market day was occasionally changed. The details of this are not clear, but one likely explanation is that it would be moved by one day if it fell on the same day as the festival of Regifugium, an event that could occur every other Julian leap year. When this happened the market day would be moved to the next day, which was the bissextile (leap) day.

The nundinal cycle was eventually replaced by the modern seven-day week, which first came into use in Italy during the early imperial period,^[12] after the Julian calendar had come into effect. The system of nundinal letters was also adapted for the week, see dominical letter. For a while, the week and the nundinal cycle coexisted, but by the time the week was officially adopted by Constantine in AD 321 the nundinal cycle had fallen out of use. For further information on the week, see week and days of the week.

Character of the day[link]

Each day of the Roman calendar was associated with a "character", which was marked in the fasti. The most important of these were dies fasti, marked by an F, on which legal matters could normally be heard, dies nefasti, marked by an N, on which they could not, and dies comitiales, marked by a C, on which meetings of the public assemblies known as comitia were permitted, subject to other constraints such as the Lex Hortensia. A few days had a different character, e.g. EN (endotercissus or perhaps endoitio exitio nefas), a day in which legal actions were permitted on half of the day only, and NP, which were public holidays.

Years[link]

Fragment of an imperial-age consular fasti, Museo Epigrafico, Rome

The calendar year originally began on 1 March, as is shown by the names of the six months following June (Quintilis = 5th month, Sextilis = 6th month, September = 7th month etc.). It is not known when the start of the calendar year was changed to 1 January. Ancient authors attributed it to Numa Pompilius. Varro states that, according to M. Fulvius Nobilior (consul in 189 BC), who had composed a commentary on a fasti preserved in the temple of Hercules Musarum, January was named after Janus because the god faced both ways, which implies that the calendar year started in January in his time. A surviving calendar from the late Republic proves that the calendar year started in January before the Julian reform.

It is not known how years were identified during the Roman monarchy. During the Roman Republic, years were named after the consuls, who were elected annually (see List of Republican Roman Consuls). Thus the name of the year identified a consular term of office, not a calendar year. For example, 205 BC was The year of the consulship of Publius Cornelius Scipio Africanus and Publius Licinius Crassus, who took office on 15 March of that year, and their consular year ran until 14 March 204 BC. Lists of consuls were maintained in the fasti.

The first day of the consular term changed several times during Roman history. It became 1 January in 153 BC. Before then it was 15 March. Earlier changes are a little less certain. There is good reason to believe it was 1 May for most of the 3rd century BC, until 222 BC. Livy mentions earlier consular years starting on 1 Sextilis (August), 15 May, 15 December, 1 October and 1 Quintilis (July).

In the later Republic, historians and scholars began to count years from the founding of the city of Rome. Different scholars used different dates for this event. The date most widely used today is that calculated by Varro, 753 BC, but other systems varied by up to several decades. Dates given by this method are numbered ab urbe condita (meaning from the founding of the city, and abbreviated AUC), and correspond to consular years. When reading ancient works using AUC dates, care must be taken to determine the epoch used by the author before translating the date into a Julian year.

Converting pre-Julian dates[link]

The fact that we use the same month names as the Romans encourages us to assume that a Roman date occurred on the same Julian date as its modern equivalent. This assumption is not correct. Even early Julian dates, before the leap year cycle was stabilised, are not quite what they appear to be. For example, it is well known that Julius Caesar was assassinated on the Ides of March in 44 BC, and this is usually converted to 15 March 44 BC. While he was indeed assassinated on the 15th day of the Roman month Martius, the equivalent date on the modern Julian calendar is probably 14 March 44 BC.

Finding the exact Julian equivalent of a pre-Julian date can be very hard. Since we have an essentially complete list of the consuls, it is not difficult to find the Julian year that generally corresponds to a pre-Julian year. However, our sources very rarely tell us which years were regular, which were intercalary, and how long an intercalary year was. Nevertheless, we do know that the pre-Julian calendar could be substantially out of alignment with the Julian calendar. Two precise astronomical synchronisms given by Livy show that in 168 BC the two calendars were misaligned by more than two months, and in 190 BC they were four months out of alignment.

We have a number of other clues to help us reconstruct the Julian equivalent of pre-Julian dates. First, we know the precise Julian date for the start of the Julian calendar (although there is some uncertainty even about that), and we have detailed sources for the previous decade or so, mostly in the letters and speeches of Cicero. Combining these with what we know about how the calendar worked, especially the nundinal cycle, we can accurately convert Roman dates after 58 BC relative to the start of the Julian calendar. Also, the histories of Livy give us exact Roman dates for two eclipses in 190 BC and 168 BC, and we have a few loose synchronisms to dates in other calendars which help to give rough (and sometimes exact) solutions for the intervening period. Before 190 BC the alignment between the Roman and Julian years is determined by clues such as the dates of harvests mentioned in the sources.

Combining these sources of data, we are able to estimate approximate Julian equivalents of Roman dates back to the start of the First Punic War in 264 BC. However, while we have enough data to make such reconstructions, the number of years before 45 BC for which we can convert pre-Julian Roman dates to Julian dates with certainty is very small, and several reconstructions of the pre-Julian calendar are possible. A detailed reconstruction giving conversions from pre-Julian dates into Julian dates is available.^[13]

See also[link]

• Ab urbe condita
• Ancient Rome
• Gregorian calendar
• Julian calendar
• Roman festivals

Notes[link]

References and further reading[link]

• Bickerman, E.J. Chronology of the Ancient World. (London: Thames & Hudson, 1969, rev. ed. 1980).
• Brind'Amour, P. Le Calendrier romain: Recherches chronologiques (Ottawa, 1983)
• Feeney, Denis C. Caesar's Calendar: Ancient Time and the Beginnings of History. Berkeley: University of California Press, 2007 (hardcover, ISBN 0-520-25119-9).
• Michels, A.K. The Calendar of the Roman Republic (Princeton, 1967).
• Richards, E.G. Mapping Time. Oxford: Oxford University Press. ISBN 0-19-850413-6.
• Rüpke, J. The Roman Calendar from Numa to Constantine: Time, History and the Fasti (trans. D. M. B. Richardson) (Wiley, 2011). ISBN 978-0-470-65508-5 (print) 9781444396539 (online).

External links[link]

• Date Conversion for Julian and Gregorian dates
• Early Roman Calendar – History
• James Grout: The Roman Calendar, part of the Encyclopædia Romana
• Roman Dates (Chris Bennett's site)
• Smith's Dictionary article

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