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Calendar
Any date that does not fall on the Kalends, Nones or Ides is calculated by counting the number of days between that day and the nearest of the three target days. The Romans had a saying: "Ad Kalendas Graecas", which means (roughly!) "Til hell freezes over", because the Greeks did not use the Kalends in their months!
The months are considered adjectives which agree with the target days of:
Kalendae, -arum, f. - 1st declension
Nonae, -arum, f. -1st declension
Idus, -um, f. - 4th declension
(These nouns only occur in the plural)
Exempli Gratia:
September 5 - Nonae Septembres: September 5 is the Nones of that month
September 2 - ante diem iv Nonas Septembres: September 2 is four days before the Nones. Dates are written in accordance with their position before the Nones, Ides, or Kalends. Hence typically the format is ante diem + [Roman numeral] + [Nones, Ides or Kalends] + [Month]
September 4 - Pridie Nonas Septembres: September 4 is the day before Nones pridie nonas, pridie idus or pridie kalendas.)
Calculating Dates
When calculating the days before the Kalends, Nones or Ides, you must count the first day. We are used to not including the first day of date range when determining the number of days, but the Romans always including the starting day.
Exempli Gratia:
September 2 = a.d. iv Nonas Septembres
Sept. 2 + Sept. 3 + Sept. 4 + Sept. 5 = 4 days
You therefore write that Sept. 2 comes 4 days before Sept. 5, counting both the 2nd and the 5th in your calculation.
To express the day before a target date: Pridie + [Kalendas, Idus or Nonas] + [Month adjective]. E.G.: Pridie Kalendas Ianuarias = December 31
To express other dates: ante diem + [the number of days prior to target date] = [month adjective]. The number is usually written as a Roman numeral, but be aware that the numbers are ordinals, i.e., first, second, third, etc.
Exempli Gratia: ante diem v (=quintum) Kalendas Septembres = August 28. We know that August has 31 days, so if we start counting back five days from the Kalends of September: 1 Sept (1), 31 Aug (2), 30 Aug (3), 29 Aug (4), 28 Aug (5).
A Brief History of the Calendar
General Info and History
The first Roman calendar, based on a lunar cycle, is said to have been introduced by Romulus. In ancient Rome, the Pontifex Minor observed the small crescent of the new moon , declared it to be a new moon and thus a new month. Romans referred to the first day of each new month as the Kalendae (Calendae) from the Latin word calare which means to call out or announce with seriousness of purpose. A new moon was sighted usually after 29 or 30 days. If clouds obscured the moon on day 30, the new moon would be declared to be on the 31st day.
The original Roman calendar was divided into ten months: Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November, December. Numa Pompilius is reputed to have added the additional two months ca. 750 BCE but maintained the beginning of the year as March 15. The Roman Senate decided to move Ianuarius to begin the year, in honor of the god of beginnings, Janus. This was about 153 BCE.
By the time of Julius Caesar the Numa calendar was three months ahead of the seasons. Winter started in September. Caesar used the Egyptian calendar as a base and establish a new calendar drawn (the Julian calendar), with 12 months of 31 or 30 days, except February, which had 29 days. Every fourth year, February had 30 days, to realign the calendar.
Some claim that Caesar, in 45 BCE, established January as the beginning of the year. We do know that Caesar revised the calendar to a solar calendar design he had borrowed from Egypt and the astronomer Sosogenes. Caesar's solar year was 365 days and 6 hours...11 min. and 45 seconds too long. so Pope Gregory XIII introduced a revised calendar in 1582.
The origin of the names for April through June are uncertain. Some ancient authors claimed that the name Aprilis was derived from Aphrodite. Others say that April was derived from aperire (to open), and claim that names of months we now call April, May and June refer to growth stages of crops or cattle.
Quintilis was renamed in honor of J. Caesar who had been born on the 12th of that month...a.d.ii ides iulias. Sextilis was renamed Augustus in honor of Octavianus Augustus who died on 19 August 14 AD (a.d.xiv Kal. Sept.)
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