Around the world, different human cultures have used a wide variety of methods to keep track of the passing year. In the western world, our calendar system is based on the Roman model, which itself underwent a series of significant changes throughout history.
"Hidden History" is a diary series that explores forgotten and little-known areas of history.
One of the difficulties in accurate calendar-keeping is that there are actually three different ways to define a “year”, and they do not agree with each other. In some ancient cultures, the year was defined in lunar terms: the cycle from one new moon to the next was 29 or 30 days, and a year was 12 lunar cycles, or 354 days. Other cultures used a “solar year”, which was the time that the Sun took to cycle once around the horizon and return to the same spot. (Many ancient cultures constructed huge stone circles as a way of marking the Sun’s position at periods such as the equinoxes and the solstices.) This took approximately 365 days. During the time of the Greek philosophers, it was found that it took slightly longer for a star in the sky to circle around and return to its original position, and this was known as the “sidereal year”. No major cultures used this as a basis for their calendar, however. Nearly everyone had a lunar calendar, or a solar calendar. And that presented the basic difficulty: there is no way to neatly fit an even number of lunar cycles inside the solar cycle, nor does a solar year fit into an even number of days. There are always days left over, and, without correction, both lunar calendars and solar calendars will fall out of step with the actual seasons, leading to things like “winter” falling in July.
The Romans tried to correct all these problems by combining a lunar cycle of months with a solar calendar of the year—a system now known as “luni-solar”.
The original Roman calendar had a series of ten months. Originally, these were likely named simply with the Latin equivalents of “first, second, third” and so on. But within a relatively short time, some of the months became known by the names of gods or goddesses. The first month (in springtime) became known as Martius, after the God of War, Mars. The second was Aprilis, after the goddess Aphrodite. Third was Maius, after Maia the Earth goddess, and fourth was Junius, after Juno, the wife of Jupiter and queen of the gods. The remaining months were Quintilus, Sextilis, September, October, November and December—after the Latin terms for five, six, seven, eight, nine and ten.
Some of these months had 30 days and some had 31, and together they added up to 304 days. But the Romans knew that the solar year was around 365 days, so they added another 61 days to their calendar during the winter. These were not part of any named month, but were called the “intercalary”, and their sole purpose was to bring the lunar calendar into tune, each year, with the solar. Measuring the progress of the solar year was the responsibility of the priesthood, known as the pontifex, and it was their job to determine when the intercalary was over and a new month of Martius would begin. It was also the responsibility of the priests to determine when the time for feast days and religious celebrations were approaching. To the average Roman citizen or slave, however, one day was the same as any other, and the passage of calendar time was of no importance (except for the religious festivals called by the pontifex).
It did not take long, however, before that long 60-day intercalary stretch became inconvenient, and so around 700 BCE the Romans reformed their calendar. Two new months were created and added to the beginning of the year. The first of these was Januarius, named after the two-faced god Janus who looks both to the future and to the past. The second was Februarius, after the februa purification rites. In addition, most of the 30-day months were now reduced to 29 days, and a few stayed at 31 days. The new 12-month calendar had 355 days.
This, of course, was still ten days short of the solar calendar, and so the Romans still needed to add an intercalary month between Februarius and Martius every few years (this intercalary was now called “Mercedonius”, because it came around the time of year known as merces, when the Roman Army was paid) to bring the two cycles back into alignment. Once again, it was the responsibility of the pontifex to decide when this needed to be done.
The new reforms also set up a standard system for naming the days of the month. Unlike our modern calendar, the Romans did not have “weeks”, nor did they number the days of their months. Instead, the first day of each month was referred to as the “Kalends”, the middle day of the month was the “Ides”, and the eighth day before the Ides was the “Nones” (“nine”, because the Romans counted the Ides as one of the nine days). So, each day of the month was referred to in terms of its position before the Kalends, Nones or Ides: the twelfth day of the month was the “fourth Ides” (again, the Romans counted inclusively), the second day of the month would be the “fourth Nones”, and the twenty-seventh day of the month would be the “fourth Kalends (of the following month)”. The day before one of the three named days was known as the “Pridie”, giving the Pridie Nones, Pridie Ides and Pridie Kalends. It was, of course, all very confusing, but the priesthood was there to keep track of everything.
As the Roman Republic fell deeper into corruption over the centuries, however, the calendar system itself was subject to political abuse. It sometimes became the case that if the Pontifex Maximus, the Head Priest of Rome, liked the particular Consuls who held office (or at least could be bribed to like them), then he would announce the insertion of a Mercedonius intercalary (coincidentally giving the preferred Consuls an extra month in office) whether it was needed or not.
By the time Julius Caesar ascended to power in 46 BCE, the whole system had become a mess. (And since Caesar’s first elected public office was as Pontifex Maximus, he had been at least partly responsible for the mess.) And now that he was the de facto emperor of Rome, Julius Caesar issued a series of reforms.
First, the number of days per month was again changed, with some months switching from 30 days to 31, and the beginning of the year was moved from the Kalends of Martius to the Kalends of Januarius. This set the length of the year at 365. To keep it aligned with the solar cycle, Caesar dropped the whole “Mercedonius” intercalary system and introduced the concept of a “leap day”, an extra day inserted once every four years.
As a result of all this, the year 46 BCE was actually 445 days long. It became known as “the Year of Confusion”. But the new Julian Calendar once again re-set the Roman Calendar into sync with the solar cycle. Caesar himself was honored by the Senate by renaming the month Quintilis to Julius. And later the month of Sextilis was renamed Augustus in honor of Caesar’s successor.
The Julian calendar remained long after the Roman Empire collapsed. It was adopted by the Roman Catholic Church and held sway throughout Europe for the next thousand years. However, the Roman calendar also had a problem: it was out of step with the solar cycle by a factor of one extra day every 128 years. By the 16th century CE, the calendar dates were ten days out of sync with the solar equinoxes and solstices. So in 1582, Pope Gregory XIII introduced reforms of his own to correct it: ten days would be dropped in October, and October 1 would be followed immediately by October 12. He also declared that the beginning of the new year would be moved to January 1. And finally, to solve the problems with the Julian calendar, Pope Gregory reduced the number of leap days: now instead of adding a leap day every four years, it would be added only if that year was divisible by 4—unless it was divisible by 100 , unless that year is itself divisible by 400.
It is the calendar system we still use today.
NOTE: As some of you already know, all of my diaries here are draft chapters for a number of books I am working on. So I welcome any corrections you may have, whether it's typos or places that are unclear or factual errors. I think of y'all as my pre-publication editors and proofreaders. ;)