Calendopaedia - The Roman Calendar

The Roman Calendar is believed to have been devised originally by Romulus (circa 750 BC), the founder of Rome. It was basically a lunar calendar and had ten months, six of 30 days and four of 31 days making a total of 304 days. The year started with the month of March and ended with the month of December. This was then followed by a gap before the next year started. The next year would start on a new moon to bring the calendar back into step with the lunar cycle. Many of the month names were based on the month number as follows :-

NameMeaning Length
1MartiusMars - god of war 31
2AprilisSee below * 30
3MaiusGoddess Maia 31
4IuniusGoddess Juno 30
5QuintilisFifth month31
6SextilisSix month30
7SeptemberSeventh month30
8OctoberEighth month31
9NovemberNinth month30
10DecemberTenth month30

* The origin of the name Aprilis is uncertain, however there are two possible explanations. It could be named after the goddess Venus whose name in Greek is Aphrodite. As several other months are named after deities this is quite a possibility. Alternately it could be named from the Latin aperire meaning 'to open'. This being a reference to the season when flowers begin to blossom or open.

In the reign of Numa Pompilius (circa 715 - circa 673 BC) two extra months were added. January (Iannarils) at the beginning of the year and February (Februarias) at the end. The total number of days in the year was now 354. One day was deducted from each month of 30 days (six) and added to the extra fifty to give two months of 28 days. As the year now had an even number of days, as did the two new months, an extra day was added to January to make the year length 355. This was done because even numbers were considered unlucky.

The calendar which we now consider to be the Roman Republican Calendar was introduced by Tarquinius Priscus (616 - 597 BC). It still had 355 days but the length of the months was changed as follows :- (using current names)

Again notice the lack of months with an even number of days. In the case of February the whole month was considered unlucky and one of the months had to have an even number to arrive at 365 as the total.

A later modification by Decemvirs changed the order of the months so that February followed January. The year was still 10 1/4 days short and so an intercalary period was introduced. This was known as Intercalans or Mercedonius and was inserted after 23rd of February in alternate years. Mercedonius was alternately 22 or 23 days in length. The remaining 5 days of February were dropped in intercalary years. This arrangement produced a four year period of 1465 days, an average of 366 1/4 days per year. This was one day too long so every 24 years further adjustment was made by dropping one of the Mercedonius months.

This was a very complicated system and still did not keep in synchronisation with the phases of the moon so the decisions as to when the intercalary month was added and how long it should be fell into the hands of a group of high priests known as the pontiffs. This power was abused for political ends and at the time of Julius Caesar the civil equinox was three months away from the astronomical equinox. This caused Caesar to order the production of a new calendar known as the Julian Calendar.

Days within the month were counted from designated division points within the month: Kalends, Nones, and Ides.

Dates falling between these division points are designated by counting inclusively backward from the upcoming division point. This means that any day after the Ides is counted back from the Kalends of the next month. For example 30th March was known as III Kalends April.

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