The first cache in this series on calendars (A week of it!) looked at the origin of the week. This cache looks at the calendar of the Roman replublic, which is the calendar Julius Caesar reformed to create the one we use today (albeit with a tweak to the leap year rule around 1600 years after Casear introduced his calendar).
You have to feel sorry for the early calendar designers. They had three natural cycles they were trying to measure and to use as the basis of a calendar: the day, the lunar month and the solar year. None divides at all evenly into any of the others. The month is currently 29.531 days, and the year 365.242 days (or 12.37 months). Also, these numbers change slowly over time (but slowly enough that calendar designers can ignore these variations). For example, the year today is around 10 seconds longer than it was 2000 years ago.
Months are a common feature of calendars. In Lunar Calendars (such as the Jewish or Islamic) great trouble is gone to keep the start of the month at a fixed phase of the moon (in the Jewish calendar, the start of each month is the new moon). To do this months are alternately 29 and 30 days (with the occassional leap day to keep things in sync). A problem is that 12 of these months is only 354 days, over 11 days short of a solar year. While the Roman Republic calendar is not a lunar calendar, it is believed to have been derived from one. Our Gregorian calendar makes no attempt to keep months in sync with the moon.
The earliest known Roman calendar, attributed to the city's founder, Romulus, dates from the eighth century BCE. It had 10 months: Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, and December. The final six are named using the Latin for the numbers 5 to 10. Six months were of 30 days and 4 months of 31 days, totalling 304.
The new year began in the spring in Martius, which contained the northern spring equinox. Spring was the time to start planting and fighting wars. The year ended 304 days later at the end of December. This was followed by a winter period outside of the calendar (presumably little of note happened in this period!). In the 7th century BCE, Etruscan king Numa Pompilius, added two new months after December, named Januarius and Februarius.
Over time this calendar evolved into the calendar of the Roman Republic with Februarius having 28 days (split into a 23 day period and a 5 day period); Martius, Maius, Quintilis, and October 31 days and the other months 29. The 355 days of this calendar is close to 12 lunar months (354 days is closer, but Romans disliked even numbers, as we can see by the number of days in each month). This calendar was 10 and a quarter days short of a solar year. So (in theory at least), every second year a leap month (Mercedonius) was added after Februarius 23 (and the last 5 days of Februarius became the last 5 days of Mercedonius). Mercedonius alternated between 27 and 28 days. This gave an average calendar year of 366.25 days, about 1 day longer than the solar year. Note that the insertion of the leap month occurred at the end of the year, just before the begining of the new year in Martius.
Unfortunately, insertion of Mercedonius was not automatic. It was at the discretion of the Pontifices (ruling council of the Roman priesthood) who often forgot to insert Mercedonius, or who decided whether to insert Mercedonious or not based on whether they liked the current officials (bribes made officials more likable), and not based on the needs of the calendar.
In 153 BCE, Januarius became the beginning of the civil year (consuls began their terms at the start of Januarius). This change from the original new year of Martius is why our 9th to 12th months have names based on the Latin for 7 to 10.
The Roman method of numbering days in the month seems very clunky to modern eyes. There were three named days in each month. The Kalends (from which the word calendar derives) was the first day of the month. The Nones was the 7th day in 31 day months (and the 5th day otherwise). The Ides was the 15th day in 31 day months (and the 13th day otherwise). It is thought that originally the Kalends was at new moon, the Nones at half moon and the Ides at full moon, but the calendar of the Roman republic does not keep months in sync with the moon (partly due to having a 23 day month in leap years).
The Kalends, Nones and Ides of each month were known by their names. All other days were expressed as the number of days to the next named day. For example March 17 would appear as a.d. XVI Kal. Apr, or 16 days before the Kalends of April. The day before a named day (say Kalends) would be prid. Kal, the day before that would be a.d. III Kal., the day before that a.d. IV Kal. and so on. Prid was short for pridie (day before), and a.d. for ante diem (days before).
This clumsy way of specifying dates persisted for centuries; right up to Shakespeare's time (his audience would have had no trouble knowing what was meant by the Ides of March). Maybe a good name for this count-down style of numbering days would be the "Are we there yet day of month numbering method".
The Roman Republican calendar has a number of familiar features. Most of the month names are familiar. The year starts in Januarius. Februarius is involved in leap years. Martius, Maius, Quintilis, and October have 31 days. The 355 day length of the non-leap year, weird leap month insertion, and strange way of numbering days are all quite foreign to us.
To work out the coordinates of this cache you will have to compute the day of the month for a number of dates in the Roman Republic calendar. For example, Id. Jan. is the 13th of Januarius (so has the value 13).
The cache is located at -43 30.ABC 172 34.DEF
A = (a.d. IV Kal. Quin.) - (a.d. VII Kal. Nov.)
B = a.d. IV Non. Mai.
C = (a.d. XVII Kal. Jan.) - (prid. Id. Mar.)
D = a.d. VIII Id. Mar.
E = prid. Non. Sex.
F = a.d. VII Id. Sep.
Given the similarities bwtween the Roman republic calendar and our own, it is surprising how foreign the dates above are!
This is the second cache of a series on history of the calendar. The caches in the series are:
- A week of it!
- Beware the Ides (and the Nones and the Kalends)
- Veni, vidi, kalendri
- Monk-eying with the Calendar
- Give us our eleven days
You can check your answers for this puzzle on Geochecker.com.
The latest replacement cache is no longer hidden under the obvious structure at GZ. It is now a black bison hidden at head-ish height, tied to a tree with fishing line. If tucked away properly. the fishing line will be easier to see than the cache. Tree is about 10 paces east of the original GZ, about a metre from the end of the wooden fence.