Episode 24: Etruscan & Roman Astronomy

December 8, 2022

Rome, the great empire of the Mediterranean, is not known for its astronomy. But while it lagged behind other civilizations, it is a mistake to think that they were entirely uninterested in the subject. Astronomical references permeated the Roman calendar and one of Rome's longest lasting contributions to Western civilization, the Julian calendar, was devised by the Roman astronomer Sosigenes.


Good evening and welcome to the Song of Urania, a podcast about the history of astronomy from antiquity to the present with new episodes every full moon. My name is Joe Antognini.

Well at long last we have wrapped up our extensive tour through Greek astronomy, starting in the Archaic Age and landing all the way in the Roman Era some nine centuries later. So at this point we have encountered the astronomy of two cultures of antiquity: Greece and Babylonia. In this episode we’ll turn to the culture that came to dominate the Mediterranean — Rome.

Now, at times I’ve rather put down the Romans for their astronomy, or lack thereof, and made snide remarks about them, saying things like “their astronomy or lack thereof.” Well, I’m being a bit unfair by saying things like that and you should know that I say it tongue in cheek. It’s easy to say something like, “the Romans had no astronomy” or “the Romans had no interest in astronomy,” but of course this just isn’t true. The Romans certainly did have an astronomy. It’s just that, relative to its neighbors, and eventual subjects, to the East, Roman astronomy was pretty paltry. And, while this comparison is a little unfair since Greek astronomy was really quite remarkable among the cultures of antiquity for its sophistication, if we broaden our horizons and look at cultures across the globe, compared to basically everyone else, from the Egyptians to the Indians, the Chinese to the Mayans, for a civilization of its staggering size, complexity, and longevity, Roman astronomy was undoubtedly at the bottom of the pack.

But again, bottom of the pack doesn’t mean that they had no astronomy at all, so in this episode we’ll look at how the Romans viewed the heavens and how these views influenced the lives of the citizens of Rome, particularly in the earlier years of the civilization.

Now, since we’re dealing with a new culture here, I think it’s helpful before diving right in to the astronomy, to just give a broad overview of the arc of the rise and fall of Rome. Of course if you want more detail about the history of Rome, you’ll have to look elsewhere, but I do hear that there is a good podcast on the subject. At the highest level, Roman history can be divided into three periods: the Roman kingdom, which emerged around the 8th century BC and lasted until the end of the 6th century, 509 BC to be specific, followed by the Roman Republic which lasts from 509 BC until 27 BC, which marks the transition to the Roman Empire, which everyone agrees lasts a long while, but sort of fizzles out at some point. The traditional end date is 476 BC when the Western Empire fell to German barbarians, but you could make the case that some form of the Roman Empire persisted in the East all the way until 1453 when Constantinople fell to the Ottomans. During this last era, as Rome subsumed the various Hellenistic empires in the East, the astronomy of Rome effectively became subsumed by the much more sophisticated astronomy of those cultures, so, in a way, we’ve already gotten to know what Roman astronomy of this time period looked like. In this episode I want to focus more on the astronomy of early Rome, when it was smaller and more isolated from the strains of Greek thought, though, as we’ll see, it was never fully independent from it.

Now when we look at early Rome, we’re looking at a frankly unimpressive civilization. If, sometime in, say, the 7th century, you collected all the civilizations of the Mediterranean and I told you that one of these civilizations would grow to be the largest empire the world had ever seen and would dominate the whole of Europe and the Mediterranean, you would look at the lot of them and say that it was probably going to be the Egyptians with the Babylonians as strong runners-up. The Greeks would have been a bit of a dark horse at that point but not an entirely unreasonable bet. If I had then clarified that this civilization would come out of the Italian peninsula you would have been shocked, but then probably would have concluded that it must have been the Etruscans that, against the odds, somehow had risen to this lofty position, and, failing that, maybe the Samnites. But you’d be forgiven for laughing when I told you that it was, in fact, the Romans who managed this feat. For the first several centuries of its existence, the Kingdom of Rome occupied a little sliver of land on the western coast of the Italian peninsula and was no more than just one city state among the dozens and dozens of city states that dotted the Mediterranean.

During the Roman Kingdom, the dominant culture on the Italian peninsula was that of the Etruscans to the north. The various groups on the peninsula, including the Romans and the Etruscans, warred and skirmished with each other over the centuries, but when Rome ultimately won out over the Etruscans, one of the great masterstrokes of Roman politics was in assimilating this conquered group into its own political order. The Roman aristocracy managed to arrange things so that they did, of course, stay on top; but the conquered Etruscan aristocrats found themselves with a surprising amount of influence for a conquered nation. Consequently much of what we think of as “Roman culture” is in fact of Etruscan origin and only comes to us by way of the Romans. Their very region, Tuscany, still bears the name of this ancient civilization. Now, up and down the centuries, from Roman times to the present, there has been debate about the origin of the Etruscan peoples. Among the ancient historians, there is a persistent trope that they migrated from the East, somewhere in Greece, maybe Tyrrhenus, maybe Lydia, maybe somewhere else, and there are some intriguing linguistic connections between the Etruscan language and civilizations to the East, even with some connections as far East as Persia. But modern genetic studies have concluded that the Etruscans were indigenous to the Italian peninsula. Now, oftentimes human migrations have been discovered first through linguistic analysis and were only later verified through genetic studies, but the Etruscans seem to be an exception where the linguistic and genetic analyses have disagreed with each other. For those of us interested in the history of astronomy, this question is really of the highest interest. There are certain features that show up fairly early on in Roman astronomy which had existed in the Greek and Babylonian civilizations to the East, the pentagram symbol for Venus and the octaeteris for instance, so it is natural to wonder whether or not the Romans had hit upon these commonalities independently, or if there had been some knowledge transfer from east to west, and, if there had been, how did it happen and when?

Now unfortunately for us today trying to understand the early days of Roman civilization, no written records from this time survive, so the earliest days of Rome are steeped in legend. According to the founding myth of Rome, it all began when one day the god Mars happened upon the mortal Rhea Silvia who was a vestal virgin and was collecting water in Mars’s sacred grove to bring to his temple. Upon seeing her, Mars raped her and for that duration of this time there was a solar eclipse. Rhea Silvia then became pregnant with twins, but as a vestal virgin, she was forbidden to have intercourse, so when the twins Romulus and Remus were born, they were to be drowned. But the servant who was tasked with this grim assignment took pity on the infants and put them in a basket and set them adrift on the Tiber. Washing up ashore downriver, they were taken in by a she-wolf who raised them until they were discovered by a shepherd name Faustulus.

Once the twins had come of age, they resolved to establish a new city, but they couldn’t agree on where the city should be founded. Remus wanted to found the city on the Apenine Hill, whereas Romulus wanted to found it on the Palatine Hill. So, they decided to consult the gods for a sign. After a short while, Remus saw six birds, which was a favorable sign. But a little while after that, Romulus saw twelve birds. Remus claimed that the gods had favored him since his omen appeared first, but Romulus claimed that the gods had favored him since he saw more birds. Their argument escalated, became physical and ultimately, Romulus killed Remus.

Now there is much that could be said and has been said about this founding myth, but I will say that given that the Romans identified the founding of their civilization with the rape of a woman followed by the murder of one of her sons by the other, I can’t help but be reminded of a sketch by the comedy duo Mitchell and Webb. In the sketch, the two play Nazi soldiers during WWII. One of them realizes that they have been wearing hats with skulls on them this whole time and plaintively asks his companion, “Hans, are we the baddies?”

Surely some young Roman, learning the tale of his civilization’s origin for the first time must have had a similar thought. Of course, this isn’t the only fratricide in founding mythology, early on in the Book of Genesis, Cain kills his his brother Abel. But at least the Jewish myth has the good sense to make Cain pay for his actions. After murdering Remus, Romulus is rewarded by founding the most powerful empire the world had known. But this does, I think, reveal something important about the nature of the Roman relationship to power and morality. They were ardent believers of Herodotus’s observation that “the strong do what they will; the weak suffer what they must.”

But beyond what this founding myth says about the Roman psyche more broadly, it does also indicate that the Romans were not uninterested in astronomy, contrary to what I may have led you to believe. After all, the foundational event of the conception of Romulus, the first king of Rome, takes place during a solar eclipse. And this detail is probably more than just a little supernatural flourish sprinkled on top of the tale, but had some deeper symbolic significance. The rape of Rhea Silvia by Mars was a physical conjunction of a god and a mortal on Earth, and for the duration of the rape, there was a celestial conjunction between the Sun and the Moon. In Roman mythology the Sun represented Apollo, a male god and the Moon represented, variously Diana or Fortuna, but either way a female goddess. Moreover, to symbolically commemorate the birth of their civilization, the new year was observed in March, the month associated with Mars. So the founding myth seems to have had an astrological significance in which a conjunction of a god and a mortal on Earth is paralleled by a conjunction of a god with the goddess of destiny in the heavens.

Now, one thing I do want to make clear is that these myths were written down much later, by Romans during the late Republic or during the Imperial Era. So these tales almost certainly tell us more about the cultural zeitgeist of that later era than they are telling us anything about the very earliest days of Rome. Unfortunately the very early history of Rome only survived through oral histories and became commingled with myth over the centuries.

Well, that is the legend of the founding of Rome, and that, of course, makes Romulus the first king of Rome. The second king of Rome was just as legendary, both in the sense that the creation of many of Rome’s social and political institutions were attributed to him, and he was legendary in the sense that it’s not clear whether or not he existed at all. This second king was Numa Pompilius, or King Numa.

Now Numa did a lot of important things for Rome, he is credited with founding the office of Pontifex Maximus, the highest priest, and in fact this title is still claimed to this day by an inhabitant of Rome, though this particular inhabitant, who also goes by the more popular title, “the Pope,” professes a rather different religion than Numa did 2700 years ago.

But for our purposes the most relevant contribution of Numa was to reform the Roman calendar. The very earliest Roman calendar is completely shrouded in mystery and legend, but is usually given the title the “Romulan calendar,” because, well, there was only one king prior to Numa, so there was no one else to attribute it to. But almost certainly this primordial calendar had been used by the forerunners of the Romans for centuries before they settled on the banks of the Tiber River. Now, the general narrative is that this calendar had only ten months. To commemorate the conception of Remus and Romulus by Mars, the new year was celebrated in March, or, in Latin, Martius. This was followed by Aprilis, then Maius, Iunius, and then Quintilis, Sextilis, September, October, November, and December. You’ll notice that there is a pretty close correspondence between the original months of the calendar and the modern day months. The only exceptions are Quintilis and Sextilis, which just meant “fifth month” and “sixth month”. The fact that the Romans observed the new year in March explains the otherwise perplexing feature of the modern day calendar where September, which seems to be telling you it’s the seventh month with the root “sept-“, is actually the ninth month, and October is the tenth month even though with the root “oct-“ it seems like it should be the eighth, and so on with November and December. The Romans were just starting their years from a point two months later than we do, so it all made sense to them. But, in a tale that will have to be saved for a much later episode, from around 1400 to 1750, various parts of Europe switched the date of the New Year from March to January, and consequently the names of the months no longer matched their order in the calendar.

Well, the strangest feature of this primordial calendar of Rome, at least if later sources are to be believed is that it only had 10 months. So once they got to December they were done and there were no more months until the new year started again in March. Consequently, a period of about 50 days during winter just didn’t exist in the calendar and wasn’t tracked. Now, it’s not clear whether or not we can trust the later sources who claim this, and they generally contradict each other about the details of how this actually worked in practice, but as ridiculous as it might sound to us today, the idea is not entirely implausible. Rome in its very earliest days was not some great geopolitical power that needed to organize large armies of people across vast distances of time and space — it was a small rabble of peasants and a few nobles and there just wasn’t a lot for anyone to do during winter. So it’s not entirely unreasonable that they just didn’t bother to keep track of the days in their calendar.

Now, this does raise the question of how they knew when to start the new year up again. One logical possibility is that they began the new year on the vernal equinox. But this is a little tricky in practice because the equinoxes are somewhat difficult to measure relative to the solstices since you would need to have a fairly accurate measurement of the directions of East and West. Another possibility which is more plausible at least to me is that they ended the year on the winter solstice at the end of December and then started the new year up again after Arcturus first became visible above the eastern horizon after sunset since in the 8th century BC this happened in late February.

Originally, the Roman calendar, like virtually every other calendar in the ancient world, was lunar. The months were tied to the phases of the moon. Now, somewhat awkwardly, the period of the moon’s phases is about 29 and a half days, so you can’t give the months the same number of days — some have to be shorter and some have to be longer. This was probably done on an ad hoc basis initially. A priest would observe the first crescent moon after a new moon and if it looked relatively thin he would declare the month to be “full” and have more days and if it looked thicker, he would declare the month to be “hollow” and have fewer days.

Well, the reforms of King Numa fixed the two biggest deficiencies of the calendar. He got rid of the weird timeless void in winter by adding two months, Ianuarius and Februarius, and he fixed the lengths of the months so that the priest, the pontifex minor to be specific, wasn’t just winging it every new moon. Now, given that the period of the moon’s phases is almost exactly 29 and a half days, the sensible thing to do here would be to give half the months a length of 29 days and the other half a length of 30 days, maybe alternating them. But that is not what happened. It seems that the Romans had certain numerological predilections, and, in particular, they had an affinity for odd numbers and an aversion to even numbers. So, being loath to assign an even number of days to a month, they gave four of the months 31 days and the rest were given 29 days, except for February which only got 28. Now, obviously it wasn’t ideal for February to have an even number of days, but February was really just taking one for the team because if February had an odd number of days, then the whole year would have an even number of days which would be a calamity of even larger proportions. Now what exactly their deal was with even numbers isn’t entirely clear. Later authors attributed these numerological associations to the influence of Pythagoras, who, as we saw back in Episode 11 viewed odd numbers as masculine and even numbers as feminine. But this was probably an anachronism since the evidence suggests that the Romans had this system in place before the time of Pythagoras.

Now, if you’ve been doing the math in your head you may have noticed that this calendar comes up short by a fair amount. This year is 355 days, whereas you know that the year is 365 and a quarter days long. So King Numa also turned to the solution that other cultures across the globe have turned to and added an intercalation month. This would be either 27 or 28 days long and occur after February and would actually cut February short to 23 days in the process. To determine which years got the intercalation month, the Romans used the 8 year cycle of the octaeteris that I described in Episode 17 about the Attic calendar.

Although the new calendar was in theory completely regular, certain rituals from the older calendar held over. In particular, after every new moon, the pontifex minor continued to observe the moon as before and would ritualistically chant “Te kalo Iuon Covella” either five times if the month had 29 days or seven times if it had 31 days, this meaning “I announce you Juno Covella.”

Now, although this calendar is often called the Numan calendar because Roman authors attributed its institution to King Numa, it’s more properly called the Republican calendar, because it persisted, largely unchanged throughout the entire Republican Era of Rome, and so it’s worth getting to know it in a little more detail.

Now the first thing that’s a little unusual about this calendar is that it was forward-looking, in contrast to our calendar today, which is backwards looking. When I say that it is, for example, the 20th of December, what I am saying is that the month of December started twenty days ago, at least if you round partial days up. But the Roman calendar worked the other way. Rather than referring to some date in the past, they would always refer to a date in the future. So what we would call the 20th of December they would refer to as 11 days from January.

Now there were three milestones in the month that the Romans would use when specifying the date: the kalends, the nones, and the eidus, better known in English as the Ides. The kalends was the first day of the new month and literally meant “register of debts” since this was the day that new loans would be issued and payments on loans were due. It wasn’t until the early middle ages that the word kalends morphed into the word calendarium and adopted the more modern meaning of being the general schedule of days in a year. But for all of us poor schlubs just trying to get by in this world, it does somehow feel appropriate that the word for calendar originates as meaning “a register of debts.”

The next milestone in the month was the none, and came on either the 5th or 7th day. None just translates to nine, so it might seem a little strange that it came on 5th or 7th day rather than the ninth, but remember that the Romans counted backwards — nine days after the none would be the Ides, on either the 13th or 15th day of the month. So, why did the position of the Ides vary? Well, in fact, it didn’t, at least from the Roman perspective. The Ides fell on the 13th of the month if the month had 29 days and on the 15th if it had 31. But because they always counted forward it was always 16 days before the Kalends of the next month. Well, originally the Nones and the Ides marked the first quarter and full moon, respectively. But after the Republican calendar was established this link was broken. Since the months had a fixed number of days and there were definite rules to say when the 13th leap month was added, the timing of the months started to drift away from the phases of the Moon. It would have done so fairly gradually — on average the length of the month was 29.58 days, but in reality the period of the Moon’s phases is 29.53, pretty close, but not exactly the same. But what was worse was that on leap years the extra month caused the average length of a month to drop down to 29 days. So every four years the phases of the Moon drifted by about a day.

But what was really revolutionary about the Roman calendar in the Republican Era is that they took this bug and made it into a feature. They just decided not to care what the moon was doing when setting their months. Sure, the Pontifex Minor would still ritualistically observe the phase of the moon, whatever it was, at the beginning of the month to declare whether or not the month had 29 or 31 days, but at this point the Moon had nothing to tell him about the length of the month because the months had ceased having anything to do with the phases of the Moon. So Rome, fairly early on, joined a small group of civilizations that had a purely solar calendar rather than a lunisolar calendar.

This switch had a big advantage in that it made it very easy to determine what the calendar was going to look like on any given year. For the purposes of our story, this almost certainly put Rome at a big disadvantage in their impact on the history of astronomy. As we saw with the Babylonians and the Greeks, a major driver of astronomical research in the ancient world was to try to figure out how long the months were going to be well in advance, since knowing what the calendar is going to look like in a year or two is important if you’re organizing large scale projects. But the Romans, being the pragmatic bunch that they were, decided not to bother with what was going on in the sky and just fixed a system of months entirely independent of it. Then they had no need to do any astronomy.

Now, because the calendar system was completely regular, Roman calendars had a feature that is maybe surprising to us today. Today we are used to the idea of a calendar being ephemeral. Come December we go out to a bookstore or order on Amazon a new wall calendar for the upcoming year and on January 1 we throw away the old one and put up the new. There is nothing as useless as last year’s calendar, it’s like yesterday’s news. But Roman calendars were not like this. Roman calendars were permanent. Wealthy Romans would have a calendar painted on the wall and there was no need to change it from year to year. Calendars were even carved into marble on a number of public monuments. Even the pocket calendars that some Romans carried on them would not be thrown out at the end of the year but used from one year to the next. The basic structure of the calendar was 13 columns, with each column representing a month. Each column would have a list of the days of the month along with any notes about special holidays associated with the day.

Now if you think about it, it is a little bit odd that our calendars don’t work the same way and are only good for the year they’re made. After all, we also have a completely regular system of months. Every year June has 30 days and every year December has 31. The only exception, of course, is February, but it seems like it would be possible to figure that out. After all, the Romans had an entire extra month on their leap years. But the difference, of course, is the weekdays. Sure, January has 31 days every year, but whether or not January 31 will be a Monday or Friday or a Tuesday will vary from year to year. Now in the modern world, weekdays play an integral role in our daily life. You go to work every Monday, your team has its weekly planning meeting on Tuesdays, your kid has piano practice on Wednesdays and swim practice on Thursdays, and of course you don’t work on Saturday and Sunday. So if you’re scheduling something in advance, it’s not enough to just know that your next dentist appointment will be on June 23rd, you need to know what day of the week that is going to be. And because seven does not neatly divide the length of the year, the weekdays associated with the different days of the months vary from year to year.

Well as it happens the Romans also had a week of their own, and this, too, did not neatly divide the length of the year. In the case of the Romans they had an eight day week, which they probably inherited from the Etruscans, but unlike in the modern world, the day of the week played a far less important role to them. In fact, the Romans did not even have names for most of the days of the week. They just referred to them by the letters A through H, though in the early days of the Republic the letter G did not exist yet, so they used the letter Z for the seventh day instead. There was only one weekday that had any significance and that was the nundina, which is a bit of a confusing name for it, because nundinae also referred to the entire 8 day cycle. To make matters even more confusing, etymologically, nundina derives from the Latin word for “nine,” even though it was an eight day cycle. The reason for this is that the Romans generally counted their days inclusively. So if today was a nundina, they would say that the next nundina would be nine days later, because they counted the nundina you started on.

At any rate, the nundinae had a variety of meanings, rituals, and associations, but the simplest analogy is that it was a sort of Roman weekend. For most Romans, the vast majority of whom were peasants and farmers after all, the nundina was the one day of the week that they could take a break from working and go into town and get all their shopping done. So the two main functions of the nundinae were as a day of rest and as a market day. But over the centuries other associations developed. Pliny, for instance, wrote that many people believed that it was bad luck to silently trim your fingernails on the nundinae.

Well the nundinae presented quite a conundrum for the Roman calendar. Because they were on an eight day cycle they changed from year to year. The way the Romans dealt with this is that in their calendars, they would have a column for each month, and running along the column, they would just have the letters A, B, C, D and so on through H. Once they got to H they would repeat again with A and just go through the whole year this way. Now the clever bit is that the nundinae were not associated with any of these letters in particular. The nundinae were just the nundinae. So if one year the nundinae happened to fall on day A, you would just remember that this year any days marked with A are the nundinae and that’s when you would go into town. When the next year came around you could just count eight days from the last nundina and figure out when the first nundina of the new year was. If it fell on, say, day D, then you would know that this year the nundinae were on day D. So the only thing that changed from one year to the next was which letter corresponded to the nundina. Well, and, of course, you’d have to remember whether the year had the 13th intercalation month or not. But other than that, everything else was exactly the same from one year to the next so there was no real problem etching your calendar in stone.

Well, there was a little more to the calendar than just the days of the month and the letter of the weekday. Now, you might be imagining a column with numbers in it starting with 1 at the top and 29 or 31 at the bottom, but this is not what a Roman calendar looked like. The Romans did not include any numbers on their calendar. After all, they just numbered the day based on how many days it was until the next milestone and they just assumed that everyone knew how to count. Instead every day was specified with a letter which indicated the legal status of the day. Most days were specified with the letter C, which stood for Comitia. We could loosely interpret this as a normal workday during which public assemblies could be held. Usually right before a series of Cs, there would be a day labelled F, which stood for for Fasti, meaning “permitted”. These were days in which it was permitted to open new legal cases. And finally there were days marked N for Nefasti, meaning “not permitted” and there were days marked NP, whose meaning is not known for certain, but could have stood for “Nefas Piaculum.” Either way, days marked N or NP acted as public holidays of sorts and legal business was not allowed to be conducted on those days.

Now this all sounds straightforward enough, but one of the main failings of the Roman calendar was in specifying how the nundinae on their 8 day cycle interacted with the various legal statuses associated with the different days of the year. A big point of tension over the centuries was that the farmers out in the countryside could only come in to town one day a week. If a farmer had a dispute with his neighbor and wanted to file a lawsuit or if we wanted to testify before a public assembly, that would be the only day he could do it. But what if that day happened to be a Dies Nefasti and public business wasn’t permitted? Should the nundina take precedence? It seems that the Romans had a complicated set of rules to determine which days would take precedence over which other ones and that these rules changed in unpredictable ways over the years.

But I’ve been drifting a little bit away from astronomy so I want to bring it back to some of the astrological undercurrents in the Roman calendar. The most direct one is to the two solstice feasts in the calendar: Fors Fortuna which celebrated the summer solstice and of course the famous festival of Saturnalia which celebrated the winter solstice. Fortuna was the goddess of destiny or fortune and “fors” meant luck or chance, so “Fors Fortuna” meant something like the goddess of good luck. Fortuna was associated with the Moon, the phases of the Moon waxing and waning just as the fortunes of man rise and fall. Well the feast of Fors Fortuna was celebrated from June 24 through 26, right around the time of the summer solstice, when the Sun enters the sign of Cancer. The feast was a time of general merrymaking and it was apparently a tradition for people to float down the Tiber during the night of the solstice. Ovid exalts the night like this:

Come, Quirities, celebrate with the goddess Fors!
On Tiber’s bank she has her royal foundations.
Speed some of you on foot, and some in the swift boat
and think no shame to return tipsy home from your ramble.
Ye flower-crowned skiffs, bear bands of youthful revelers
and let them quaff deep draughts of wine on the bosom of your stream.

Half a year later it was the winter solstice and the Romans then celebrated Saturnalia from December 17 through 23. As the name implies Saturnalia was dedicated to the god Saturn. Like Fors Fortuna, Saturnalia was a time of general revelry and merrymaking and also fell into the category of what anthropologists call role reversal holidays. During Saturnalia, the normal social order would be upended. Slaves would dress as freemen and their masters would wait on them at the table.

Well, there was a fitting astrological connection between these two festivals. The Moon is the closest celestial body to the Earth and therefore moves the fastest, and Saturn is the most distant and moves the slowest. So on Fors Fortuna when summer has begun, the Romans celebrated the full flower of life. Saturn, by contrast, being distant, cold, and slow, was associated with old age and death, and appropriately was commemorated just as winter began. But beyond this, the Romans also saw the signs of Cancer and Capricorn as having special significance. The sign of Cancer is the northernmost zodiacal sign on the ecliptic and Capricorn is the southernmost sign. They therefore considered these signs to be gates to the afterworld. When the Sun entered Cancer on the summer solstice, souls could more easily descend to Earth through the gates of Cancer. And on the winter solstice as the Sun entered Capricorn, souls found their ascent to heaven facilitated. So these two feasts, on opposite ends of the year, encompassed the whole cycle of life.

Well, there was another cycle of feasts that had different astronomical connections. These were a set of four or five feasts that commemorated different stages of a woman’s life, mostly centered around marriage and pregnancy, and they all had a connection to the motions of Venus. Now, Venus seems to have been associated with the feminine in many western cultures for quite a long period of time, which suggests that its origins as a female deity go back much further than recorded history. Venus’s orbit fit in well with the Roman eight year calendrical cycle of the octaeteris. In this period of eight year, Venus goes through almost exactly five cycles. If you note, for example, which sign Venus is in at inferior conjunction, then wait about 1.6 years when it arrives at inferior conjunction once again and note its sign, and then do that four more times, you’ll find that its positions trace out the shape of a pentagram, which is why Venus was frequently represented with that sign in Roman iconography, though this was by no means unique to the Romans. This symbol was also in use by the Greeks and Etruscans, along with the Egyptians and Babylonians and can even be seen in artifacts as far away as Kazakhstan, although the connection of that particular artifact to Venus is a little more tentative. But at any rate, the Romans had long associated the cycle of Venus’s motions with the phases of a woman’s life. The poet Catullus wrote a wedding song to extol the effect of Venus on marriage. In one part the boys sing:

The Evening Star is here, young men, so rise: The Evening Star
At last brings heaven its long-awaited bodies of light.
Now it is time to rise, time to leave the well-stocked tables.
Now a young maiden will come; the wedding refrain will be sung.

The girls then sing:

You maidens, do you see the young men? Rise to face them.
The Night-bringer no doubt reveals Otean fires.
Evening star, what heavenly body is borne more savagely through the sky?
You, who can tear a daughter away from her mother’s embrace,
Tear a daughter away from her mother’s embrace though she holds fast.
And give the chaste girl to a young man on fire?

Followed by the boys:

Evening star, what heavenly body shines more delightfully in the sky?
O you, who strengthen with your flame a wedding pledged.
Which young people and parents have fixed in place beforehand.
They did not join bride and groom before your blaze carried itself away.
What thing more desired do the gods give at a happy hour?

This reference to “joining bride and groom before your blaze carried itself away,” refers to it being good luck if Venus was visible in the evening sky on a wedding day. But the cycle of holidays around weddings and pregnancies were also fixed into the calendar itself.

Now I mentioned earlier that the Romans celebrated their New Year on March 1. At least that’s usually what they did, there were some periods where the date of the new year was shifted to January 1. But March 1 was the typical date of the new year and as I described earlier this was because in Roman mythology Romulus, the founder of Rome, was conceived by Mars. So in a sense the new year commemorates the founding of Rome. 15 days later, on the ides of March, the Romans celebrated the festival of Anna Perenna. This festival commemorated a rather amusing story in Roman mythology in which Mars became obsessed with Minerva, the goddess of wisdom, but evidently had little luck with her. So he went to Anna Perenna, who was born mortal but gained immortality in a story that would take me too far afield. Mars cajoled Anna Perenna into convincing Minerva to sleep with him, and Anna Perenna agreed to take on the task. But instead of actually doing that, she just waited a while and then told Mars that Minerva was now ready for him. On the appointed day Anna Perenna dressed up as Minerva and put a veil over her face and waited in Mars’s bedchambers. When Mars lifted the veil he realized that Anna Perenna had made him into a fool.

Well it’s perhaps appropriate then that the festival associated with Anna Perenna had a special place in the hearts of Roman bachelorettes and many of the festivities had something of the character of a bachelorette party. This was commonly the day when preparations were made for Veneralia two weeks later, which was a feast that was closely associated with weddings and I’ll describe in more detail in a bit. But, on the festival of Anna Perenna, bachelorettes would drink and sing vulgar songs, which would fit in well with any bachelorette party of today. Less likely to be seen at a modern bachelorette party, even in Vegas, the women would also pour menstrual blood onto the sacred orchard of Anna Perenna, and for any women who were to be married there were ritualistic inspections to ensure that they were “viripotens,” that is, of marriageable age, and “integra,” that is, shall we say, intact.

Well the historian of science Leonardo Magini made the intriguing connection that if you start at the new year on March 1 at the beginning of the cycle of intercalations, and you then wait one Saros cycle, you will end up on the date of March 15, 18 years later. Now you might recall that the Saros cycle is a pattern of lunar and solar eclipses that repeats every 18 years or so, and in Rome’s founding myth, the conception of Romulus, and by extension the whole of Roman civilization, was marked by a total solar eclipse. So, we would expect that there would be another solar eclipse on March 15, 18 years later. And this, of course, was the time at which a woman or man would be old enough to marry. Now I suspect that this connection to the Saros cycle is just a coincidence. There is no other evidence that the Romans were aware of the Saros cycle when these feasts were instituted. But, if it is the case that the Etruscans did in fact migrate from the East, it is at least possible that they may have brought with them some of the more advanced astronomy that was known to the Greeks and Babylonians and that this knowledge could have embedded itself in the calendar in subtle ways.

At any rate, about two weeks after the feast of Anna Perenna was the feast of Veneralia on the Kalends of April, or April 1. This was a day associated with weddings and was the most propitious day of the year to get married. On this day a group of women would take a statue of Venus into the male baths, and there they would undress the statue, wash it, dry it, and then dress it in white garments and decorate it with jewellery. Then the women would themselves bathe and offer incense to Fortuna Virilis, who was “the goddess of good fortune in men.” And finally they would drink poppy ground with milk and honey.

71 days after Veneralia was the festival of Matralia on June 11, which was seen as the most propitious day of the year to conceive a child. The date chosen here does not seem to be arbitrary. 71 days is the time it takes Venus to move from inferior conjunction to greatest western elongation. So if Veneralia represented the optimal time to wed, once Venus entered its next station, this then represented the optimal time for a woman to enter the next stage of her life and conceive a child. Matralia was then followed by Carmenta Antevorta and Carmenta Postverta about seven months later on January 11 and 15. Not only was this seven months after Matralia but if you go an extra year around the calendar it was also about 584 days after Matralia, which is the synodic period of Venus. At this point, a woman who had conceived on Matralia would now be nearing the end of pregnancy. This is an especially perilous time in a woman’s life, especially before the advent of modern medicine, and so she would visit two temples to Carmenta, the goddess of childbirth. One of these was dedicated to Carmenta Postvorta and the other to Carmenta Prorsa or Antevorta. The two represented the two positions the baby might be in — the former being head down, and the latter being the far more dangerous position of breach where the feet are down. This, then, was the day to ritualistically beseech the goddess that the child be oriented head down. Then, two months after Carmentalia, the child would be expected to be born in March 9, right in the middle of the new year’s celebrations.

So that’s a flavor of some of the astrological undercurrents in the Republican calendar. Now as I mentioned earlier one of the great strengths of the Republican calendar was that it was all automatic, at least in theory. The lengths of the months were fixed and there were rules around when to add leap months. But it seems that over the centuries these rules got bent more and more over time until they were ignored all together. How exactly this happened is not well described in the sources but we can imagine that it probably started out innocently enough. The eight year octaeteris cycle that the Romans used was pretty good, but not as good as the 19 year Metonic cycle. So over the centuries the months started to drift away from where they were supposed to be. The vernal equinox would start to occur in February and the winter solstice in November. An all around bad time. So, presumably, every now and again the pontifex minor or some other official may have made an ad hoc correction to the calendar by inserting an extra intercalation month to correct things a little bit and get the seasons to line back up with the calendar. But any allowance for ad hoc corrections is an invitation for mischief.

After all, the terms of Roman politicians were usually set in years. If there was a consul you liked whose term was going to expire at the end of the year, a pontifex minor could declare that there was an extra intercalary month this year and effectively add an extra month to the consul’s term. Conversely, if you didn’t like the consul and wanted to kick the bums out, you could remove an intercalary month that was supposed to be there and effectively shorten his term by a month. Now, in theory these corrections could have gone either way, but it probably says something about the nature of politics that there was a strong bias towards eliminating the intercalary month when it was supposed to be there — that is, whoever was setting the calendar on the whole clearly did not like the people in charge and wanted to get them out as quickly as possible.

So, although the rules of the octaeteris that the Romans were supposed to follow produced a year that was on average a bit too long, the problem the Romans actually had in practice was in the opposite direction. They didn’t add as many intercalary months as they should have, so what actually happened was that the vernal equinox started to occur in April and then May and the winter solstice in January and then February.

Now it seems that no one really did anything about this unfortunate state of affairs for a long time until a charismatic general by the name of Julius Caesar came along in the 1st century BC. It would be wonderful for the narrative of this podcast if I could tell you a little story about how Caesar was on some campaign out in Gaul and was expecting a legion of reinforcements to arrive but nearly lost a battle because there was a mix-up with the calendar and from that point on resolved to reform the calendar so that this mistake would never injure Rome again. But there is no such story. It’s not really clear why Caesar took an interest in reforming the calendar. The story that actually gets told is that after he had conquered Egypt he held a feast in Alexandria and during the evening spoke with a man name Acoreus, who was reputed to be the wisest man in all of Egypt of the time. The two spoke on many matters but Acoreus told Caesar all about the Egyptian calendar, which as far as calendars go, ancient or modern, probably takes the honor for being the all time most rational calendar, maybe tying with the French revolutionary calendar. Caesar was evidently impressed and resolved to appropriate some of the lessons of the Egyptian calendar into the Roman calendar. But other than this dinnertime conversation, there was no immediate event that triggered the reform.

To design the reforms, Caesar recruited a Roman astronomer by the name of Sosigenes. We don’t know much about Sosigenes except that he was he was an astronomer who worked on Caesar’s calendar reforms, but one other detail of his work that does survive is that he had made observations of the orbit of Mercury and had determined that it never drifted more than 22 degrees away from the Sun. As I’ve mentioned before, Mercury is a challenging planet to observe because it only appears briefly after sunset or briefly before sunrise. So to have measured the bounds of Mercury’s greatest western and eastern elongation would have meant that Sosigenes must have been quite an accomplished observer. But unfortunately whatever else he did has been lost to the mists of time.

At any rate, Sosigenes led the commission that was in charge of designing the new calendar. Now it perhaps speaks to Caesar’s qualities as an administrator that he didn’t do the thing you might expect a power hungry dictator to do. Having control over the calendar was a lot of power — you could keep allies in office longer and kick enemies out of their positions sooner. So you might have expected it to work like redistricting commissions in many states in the modern US. The commissions get stacked with supporters from one party or the other and they gerrymander the district boundaries to give themselves the maximum political advantage. It’s relatively unusual for states to have some sort of a non-partisan redistricting commission because why would the people in charge give up that kind of power? Nevertheless, that’s exactly what Caesar did. Rather than stacking his calendar reform commission with his own supporters, he chose people who, like Sosigenes, were competent but not political.

The commission seems to have worked fairly quickly. Within two years of Caesar first proposing the idea, the new calendar had been established and was started to be rolled out. This new calendar, called the Julian calendar was really quite a brilliant combination of both astronomical and timekeeping engineering alongside shall we say social engineering, or at least political nous. In a few fundamental respects this new calendar was radically different from the old calendar, but was designed in such a way that the impact of these changes to ordinary people was minimized as much as possible.

The first big change was that the new calendar abandoned the ancient Roman bias against even numbers. Rather than restricting the lengths of the months to 29 or 31 days, the months now became either 30 or 31 days long, with February remaining at 28 days. Plus, a few of the shorter months got promoted into longer months. In the original Republican calendar, January, Sextilis, and December were 29 days long, but in the Julian calendar they all got 31 days. The net effect of this was that there were an extra 10 days added to the calendar, so the 12 months of the year went from being 355 days to 365 days.

Now the masterstroke was that because they were only a quarter day off from the true length of the year, they didn’t need to be adding in an entire extra month every few years. Instead, they could just add a single extra day to the year every four years. Since intercalations were normally performed after February, they kept to this practice and added the leap day to the end of February, which made sense anyway because it’s the shortest month. Moving from a leap month to a leap day was really the genius of the Julian calendar because it almost completely eliminated the temptation to meddle with the calendar for political advantage. A month is a long time — anyone in politics knows that a lot can happen in a month. If you can lengthen an ally’s term by a month or shorten an enemy’s term by a month, that can be quite a lot of power under the right circumstances. But if you’re only allowed to add or remove a single day, that is considerably less power. There would be vastly fewer instances where it would be worth making that change. Plus, in the old system, the rules for adding in the leap month were fairly complicated and didn’t match up with the seasons all that closely, so you could always cover your meddling with the fig leaf of claiming that you were just trying to realign the calendar with the seasons. But the length of the year is really quite close to 365 and a quarter days, it’s off by less than 12 minutes. Even if you did arbitrarily add or subtract an extra leap day you’d only change any misalignment by a day — not much in the grand scheme of things. So the Julian calendar reform had the effect of almost completely removing the calendar from the whims of politicians.

Now, although from a sort of engineering perspective the Julian reform had changed the calendar in fairly fundamental ways, for the commoner, the new calendar didn’t feel all that different. Not different enough, anyway, for anyone to make a big fuss about it, which was the main point. Sure some of the months were a bit longer now, and some of them had even days, but the lack of the intercalation month was probably a welcome simplification to most people. But other than that, there wasn’t a big difference. The months retained the same names, the long months were still long and most of the short months were still short. The 8 day cycle of the nundinae continued uninterrupted throughout it all. And each month had its usual Kalends at the beginning, Ides in the middle, and Nones nine days before that. It’s interesting to contrast the success of the Julian calendar reform with another ambitious calendar reform that had less success, the calendar of Revolutionary France. In both cases the calendar was fundamentally reworked into a form that was believed to be more rational. But in the Julian reform, the commission painstakingly tried to make things appear as close as possible to the way they were before. In the case of Revolutionary France, the goal was the opposite. They deliberately broke with tradition at every possible turn. The months all got new names. They started in new places — the first of each month in the new calendar would fall around the 20th of a month in the old calendar. And — with this was its undoing — they changed the week from being 7 days long to 10 days long. This proved to be its downfall. Although the French continued to humor their new calendar for a little while after things had calmed down and Napoleon had seized power, workers only got one day every 10 days now instead of every seven. Now, the designers of the revolutionary calendar had actually thought this through, and workers were supposed to get a half day off halfway into the week to compensate — this actually increased the total amount of time off in a year by a day. But people tend to value a full day off more than two separate half days off. So, when the terror had become a distant nightmare in the past, the French government quietly abolished the calendar reforms and reverted to the original calendar. Now, perhaps the immediate moral of this is that you can do whatever you want to the calendar just as long as you don’t mess with people’s time off. But perhaps the meta-moral here is that you don’t always know a priori what changes will be popular and which won’t, so if you are going to make reforms and want to make them to stick, it’s best to present them in a way that makes them appear as minimal as possible.

Well, the designers of the Julian calendar did try to heed to that principle, but there was one respect in which they really had little choice but to make one temporary upheaval. The calendar itself was quite, well maybe beautiful isn’t exactly the right word, but it was designed well for the job it had to do. The problem was that over the centuries the existing calendar had drifted almost two months off from where it was supposed to be. So, to start the new calendar off on the right foot and reset all the timings, Caesar declared that right before the new calendar was take effect, the year would have not one, not two, but three intercalary months. Consequently the year 46 BC was 445 days long and holds the record for being the longest so-called year recognized by any state in history and gained the appropriate nickname “annus confusionis,” or “year of confusion.”

But, the hope was that with one quick rip of the band-aid everything would once again be right and the new calendar would seamlessly bear the Roman state into a bright future for all eternity. Unfortunately, however, things did not work out that way. Almost immediately, the new calendar began to go off the rails. The idea of the calendar was that the year is about 365 and a quarter days long. So you have a cycle where the first three years are 365 days long and then every fourth year you add in a leap day to bring the average to 365 and a quarter.

The problem was that the Romans started adding the leap day every third year instead of every fourth. The fact that this happened is well attested. There are six separate sources which all write about how leap days were getting added at the wrong frequency. But what’s less clear is why this happened. There are a few theories, though they are all necessarily somewhat speculative. One theory is that it was an act of sabotage by Caesar’s opponents. The new calendar was closely associated with Caesar and he was a figure who was certainly polarizing. So maybe a cohort were deliberately trying to disrupt one of his big reforms. The problem with this theory is that the people in charge of the calendar were either politically neutral or on Casear’s side. It didn’t really seem to be in any of their interests to sabotage the new calendar.

Another theory is one of incompetence. The administrators just didn’t understand what they were supposed to do and messed it up. Again, though, this theory doesn’t seem entirely plausible to me. After all, the people running this thing were pretty clever, and to be frank, it’s just not that complicated.

The most compelling theory to me is that it was best described as a legislative bug. The idea is that the legislation had been crafted a little inartfully and accidentally specified that leap days were to be added every three years instead of every four. This is not as unlikely as it might seem. The Romans oftentimes counted dates inclusively. We saw earlier how the nundinae came from the root “nine” even though it was an eight day cycle. In the Roman system they counted the days until the next nundina including the current nundina, so that the nundina was effectively counted twice. So if the legislation for the new calendar had been worded in the same way that dates usually were, saying that a leap day was added to every fourth year would have meant, if you start on a leap year, add a leap day four years later including the current year, which would in effect have added a leap day every three years instead of four.

If this is the case, the administrators in charge of setting the calendar would have known that they were adding leap days in the wrong years, but there was nothing they could do about it — their hands were tied. After all, one of the main motivations for the reform was to remove any discretion from the administrators of the calendar. At any rate, this farce continued for a full 36 years before the mistake, whatever the cause, was corrected by the Emperor Augustus.

Well, the calendar underwent a few more minor reforms over the centuries, but only two are really relevant to us today. Earlier in this episode I went through the month names and they all sounded familiar enough, Ianuarius, Februarius, etc. all the way through December. But there were two exceptions: Quintilis and Sextilis which took the place of July and August. Well these two months were renamed in honor of the two Roman leaders I’ve mentioned: Julius Caesar and Augustus. The Roman Senate voted to rename month of Quintilis to Julius, which gets anglicized to July, in honor of Julius Caesar shortly after he was assassinated on the Ides of March in 44 BC, just one year after his new calendar had taken effect. About a half century later, the Roman Senate decided to repeat the honor this time for a living emperor rather than a dead dictator and renamed Sextilis to August in honor of the Emperor Augustus.

Well I think it is fair to characterize the Julian calendar as a remarkable triumph. It was certainly one of the longest-lasting institutions produced by Rome, and outlasted the empire by more than a millennium. The Roman calendar, particularly the Julian calendar, was unique on a few fronts. Firstly, it was a purely solar calendar in a time when that was quite unusual. Second, it was standardized. In Hellenistic Greece, you could, of course, travel far and wide to Greek city-states and colonies all across the Mediterranean and you could communicate with the locals in Greek wherever you went. Maybe Greek in a very different dialect, but something that was recognizably Greek nonetheless. But every city-state kept its own unique calendar with its own unique months and its own unique rules for how the months would be set. But in the Roman Empire, you could travel anywhere across the Mediterranean and it would be the Ides of March just as much in Alexandria or London as it was in Rome. In fact some of the preserved calendars found in different parts of the Roman Empire have feasts recorded on them that could only properly be celebrated at particular temples in Rome. But Rome was at the center of the empire and for many centuries managed to impose its version of time across a vast geographic expanse. After being a solar calendar and a standardized calendar, the third reason that the Julian calendar was so successful was thanks to its accuracy. Its assumption that the year was 365 and a quarter days long was only 12 minutes off from the correct value. So unlike lunisolar calendars that had to repeatedly correct their system of intercalations, the Julian calendar could just chug along unmodified for centuries. Now it wasn’t perfectly accurate — that 12 minute drift every year did add up. But it took more than a millennium before it got bad enough that anyone had to do something about it, so it will be some time before we arrive at those changes in this podcast. In fact, it’s good enough that to this day the Orthodox Christian Churches continue to use the Julian calendar for their liturgical timekeeping.

Now, when I originally set out to write this episode I intended to cover all of Roman astronomy in just a single episode. But the transition of Rome from republic to empire is a decent place to make a break before we continue with the astronomy and astrology of the Roman Empire. Nevertheless, that will not be what I talk about in the next episode. The next full moon happens to fall on January 6, which is Three Kings Day, which is one of the biggest holidays in Latin America, that celebrates the Adoration of the Magi, who, in the story, followed a star in the sky to find the infant Jesus. Now, given that we ended this episode around the turn of the millennium in the Roman Empire, this seems like as good an opportunity as any to talk about an astronomical event that otherwise doesn’t really fit neatly anywhere else — the Star of Bethlehem, which has intrigued astronomers for centuries. What was it — and, more to the point — did it actually exist? I know I keep saying this, but it will be a slightly shorter episode due to the holidays, but after that we’ll pick back up with Roman astronomy in late antiquity. I hope you’ll join me then. Until the next full moon, good night and clear skies.

Additional references

  • Magini, Leonardo, Stars, Myths and Rituals in Etruscan Rome
  • Rüpke, Jörg, The Roman Calendar from Numa to Constantine