The Common Era system -- or CE/BCE (AD/BC, for many Christians) -- didn't always exist. How it came to be is a pretty simple story. In the 3rd and 4th centuries, Christian chronographers calculated that Christ was born in 1 CE. (They were probably mistaken over which year Jesus was born, but there's no doubt about the number of years since 1 CE.) The first time anyone actually specified a date using Jesus' supposed birth as a reference point was in 525 CE, in a tract by the entertainingly named Dionysius Exiguus, or 'Dionysius the Insignificant'. (Here's a translation of his On the Paschal Cycle, if you're interested: the relevant section is under the heading Argumenta Paschalia, 'First argumentum'.)
A couple of hundred years later, in the 8th century, the Northumbrian scholars Bede and Alcuin followed Dionysius' lead, and Bede coined the phrase anno Domini 'in the year of the Lord'. And so the AD system gradually took off. Because really, in western Europe by that time, there weren't any other good systems to use.
So how did the ancient Romans number years before that? Popular belief has it that they used a system called 'AUC', standing for ab urbe condita 'from the founding of the city [of Rome]'. The legendary date of Rome's founding was 753 BCE, so
1 AUC = 753 BCE(For years CE, add 753 to find the year count in AUC; for BCE, subtract the BCE year-count from 754. We have to have separate formulas for CE and BCE, because there was no year 0, and that messes things up. Except astronomers: when discussing astronomical events in the past, they use negative year-numbers instead of BCE, so astronomical year 0 = 1 BCE, year -1 = 2 BCE, etc.)
2 AUC = 752 BCE
753 AUC = 1 BCE
754 AUC = 1 CE
2769 AUC = 2016 CE
Trouble is, the AUC system is very nearly a myth. Hardly anyone ever used it for dating purposes, until the tail-end of Rome's imperial dominance. For one thing, Rome's founding wasn't dated to 753 BCE until the great scholar Varro, early-ish in the principate of Augustus. Obviously the AUC system couldn't have existed prior to that. For another thing, scarcely any writers use AUC dates until at least the 3rd century: we really start to see it in Censorinus, and more so in 4th century histories and historians like the Chronography of 354, Eutropius, and Orosius. These last two were writing at a time of intense Christianisation, not long before the Roman state was divided into western and eastern empires, and fewer than 150 years before Dionysius the Insignificant!
Prior to that, Varro's date for the founding of Rome crops up mainly in connection with jubilees, like the 800th jubilee in 47 (in the reign of emperor Claudius) and the 1000th jubilee (under Philip). Even in Eutropius' history, the opening paragraph reads:
Romanum imperium ... a Romulo exordium habet, qui ... urbem exiguam in Palatino monte constituit, XI. Kal. Maii, Olympiadis sextae anno tertio, post Troiae excidium ... anno trecentesimo nonagesimo quarto.
The Roman empire takes its origins from Romulus ... He founded a small city on the Palatine hill on the 21st of April, in the 3rd year of the 6th Olympiad1 ... in the 394th year after the destruction of Troy.2
1 '3rd year of the 6th Olympiad' is faithful to Varro's date. That year ran from 754 to 753 BCE, or 754/3 BCE for short: in Greek calendars the year began and ended in midsummer.
2 Eutropius puts the fall of Troy in 1147/6 BCE. Legendary though it is, the fall of Troy was a central starting point for Hellenistic chronographers. Extant sources give us at least a dozen different dates for it, ranging from 1335/4 BCE (Douris of Samos, FGrHist 76 F 41a, subscription required) to Eutropius' 1147/6. Eutropius was probably following the 4th century BCE historian Ephorus, who put it in 1149/8 BCE (FGrHist 70 F 223, subscription required); the discrepancy can easily be explained as a result of one source or another using inclusive counting for multiple consecutive intervals.
Eutropius has to resort to two other year-numbering systems to get his message across. AUC wasn't something he could take for granted: he subordinates it to the Greek system of counting Olympiads, even writing in the 4th century, not long before the abolition of the Olympia. As his history progresses he mentions AUC dates, but only occasionally.
The other contexts where we see AUC dates are
- the Capitoline fasti consulares from Augustus' reign, listed alongside consuls' names (but replaced from 23 BCE onwards by Augustus' regnal years, starting from when he accepted tribunicia potestas in 23 BCE);
- three places in Livy's history (3.33.1, 4.7.1, 5.54.5);
- three references to lost republican-era historians in the works of Pliny the Elder, Censorinus, and Macrobius (Cassius Hemina fr. 20, fr. 26 ed. Peter; L. Calpurnius Piso fr. 36 ed. Peter);
- a single coin from Hadrian's reign; and
- a discussion of chronography by Aulus Gellius (Attic nights 17.21).
|Part of the Capitoline fasti showing second consuls for part of the 4th century BCE:|
one of the handful of documents that actually use the AUC system.
The years listed (circled in red) are inconsistent with Livy's chronology.
Basically, no one cared about AUC. AUC was never a thing. Stop trying to make it a thing!
So how did the Romans refer to years? The answer is simple but messy: they used a system of eponymous years. Years were referred to by the names of the most important patrician office-holders, the two consuls. So: 100 BCE was 'during the consulship of L. Valerius Flaccus and C. Marius'; 44 BCE was 'during the consulship of C. Iulius Caesar and M. Antonius'; 1 CE was 'during the consulship of C. Caesar and L. Aemilius Paullus'.
If that sounds horrid and untidy ... well, it's because it is. To navigate a system like that, you need a list of who the consuls were in every year. And that's exactly how Roman historians did it. The consul lists were called fasti consulares, and were a matter of public record. We have several fragmentary consular fasti, like the Capitoline fasti cited above. To measure an interval of years, you didn't simply subtract one date from another: you had to go through a list of names, counting each year one by one. That kind of system also leads to errors: all dates in Roman history before 300 BCE are uncertain by up to three or four years, because of incompatibilities between the Varronian fasti and Livy's history.
The eponymous consular system was far from universal, even within the Roman world. Under the principate, consuls were often sidelined in favour of the emperor's regnal year. And the consuls were closely associated with Rome itself: lots and lots of other calendars continued to exist elsewhere, with their own year-numberings. Most of them were regnal years, in the case of client kingdoms. Some places used eponymous years relating to local magistrates, like the archons at Athens.
|A selection of year-numbering systems|
(Coloured bars indicate periods of widespread usage,
not year 1 according to the system!)
Olympiads were reckoned starting from 776/5 BCE: 776/5 was the 1st year of the 1st Olympiad, 772/1 was the 1st year of the 2nd Olympiad, and so on. It doesn't matter that the Olympia festival probably wasn't first celebrated in 776/5 -- just as it doesn't matter that Jesus probably wasn't born in 1 CE. Those are still the years that serve as the origin point for the year-numbering. The Olympiad system was only really commonly used by chronographers: it never enjoyed popular use. The first person to use it as a general-purpose dating system was the late 4th/early 3rd century BCE historian Timaeus of Tauromenion. Later in the 3rd century, Eratosthenes' chronographic work confirmed its role as the standard measuring rod for ancient historians, a role it kept for the next six centuries -- and beyond: after the early Byzantine campaign against pagan Hellenism petered out, Olympiads regained their popularity for a while under the Macedonian dynasty, notably in a 10th century encyclopaedia called the Suda.
The Seleucid system was simpler still: it was a plain count of years since 312/11 BCE, the beginning of Seleukos I Nikator's reign over the Seleucid Empire. Unlike the AUC and Olympiad systems, the Seleucid era count was used popularly throughout the eastern Roman empire and throughout central Asia as far as Afghanistan, not just by historians. The year-count outlived the Seleucid Empire itself: Hellenistic Jews used the Seleucid system for historiographic purposes until Hillel II fixed the Hebrew year in 359/60 CE, and Syriac historians used it for centuries longer still. Arabic scholars sometimes called it the 'Roman era' (târîch el rûm), 'era of Alexander' (târîch Iskender), or 'era of the two-horned one' (târîch dhû-l-karnaini), also referring to Alexander.
By the way, speaking of jubilees: just five years from now, 21 June 2021 will be the start of the first year of the 700th Olympiad. Start planning a party now!
Feeney, D. 2007. Caesar's calendar: ancient time and the beginnings of history, U. of California Press, esp. pp. 139-42, 167-93.
Hannah, R. 2005. Greek & Roman calendars: constructions of time in the classical world. Duckworth, esp. pp. 148-52.