When dating began

That is a blatantly clickbait-and-switch post title. Anyone expecting to read about the origins of romantic outings involving two people will have to look elsewhere. What this post is about is how the idea of assigning consecutive numbers to the years originated.

We now routinely assign a numbered year to events in recorded history, so that I can write that Bishop Ussher’s year of the creation of the Earth was 4004 BCE or that the American revolution was in 1776 CE. This sequential numbering of the years enables us to immediately fix an event in relation to other events. The system seems so natural that one feels that it must have always been in place and did not have to be invented at all, let alone have a definite beginning. But classicist Paul J. Kosmin says that there was a time when this system of numbered years did not exist and that events were placed in a historical sequence using various circumlocutions that had only local validity.

For from earliest recorded history right up to the years after Alexander the Great’s conquests in the late 4th century BCE, historical time – the public and annual marking of the passage of years – could be measured only in three ways: by unique events, by annual offices, or by royal lifecycles.

In ancient Mesopotamia, years could be designated by an outstanding event of the preceding 12 months: something could be said to happen, for instance, in the year when king Naram-Sin reached the sources of the Tigris and Euphrates river, or when king Enlil-bani made for the god Ninurta three very large copper statues. Alternatively, events could be dated by giving the name of the holder of an annual office of state: something happened in the year when two named Romans were consuls, or when an elite Athenian was chief magistrate, and so on. Finally, and most commonly in the kingdoms of antiquity, events could be dated by counting the throne year of the monarch: the fifth year of Alexander the Great, the 40th year of king Nebuchadnezzar II, and so on.

Each of these systems was geographically localised. There was no transcendent or translocal system for locating oneself in the flow of history.

Where we would write, simply, ‘431 BCE’, Thucydides was obliged to synchronise the first shot of [the Peloponnesian] war to non-overlapping diplomatic, religious, civic, military, seasonal and hourly data points. The dates are intimately tied to central state institutions, dependent on bureaucratic list-making, applicable only within a self-limiting geography, and highly sensitive to political change. Indeed, they are not really dates at all, so much as synchronisms between multiple events, coordinating a network of better and lesser-known occurrences: what is being dated, and what dates it, belong to the same order of things. Imagine giving the date of the invasion of Iraq, your grandma’s birth or American independence in such a manner; and then try to explain this to someone from another country.

So when did people adopt the current system? Kosmin says that it began in the year we now fix as 311 BCE, following the death of Alexander the Great when one of his generals went on to form an enormous kingdom stretching from Bulgaria to Afghanistan. The numbering system is named after this general and called the Seleucid Era.

The Seleucid Era began from Year 1 (set at Seleucus I Nicator’s arrival in Babylon in spring 311 BCE) and continued counting, getting bigger each year: n+1. At the death of Seleucus I, his son Antiochus I did not restart the clock, and nor did any of his successors. For the first time in history, historical time was marked by a number that never restarted, reversed or stopped. It is still going. This was time as we know it – 2019, 2020, 2021, and so on – a transcendent, universal, absolute, freestanding, regularly increasing number. It was unconnected to political events, the life-cycle of rulers or conquest. It was not dependent on an imperial bureaucracy or a scribal elite. It could be used at distance to correlate events.

The number could now be affixed to all manner of objects and documents, unambiguously dating its origin.

It is interesting is that this Seleucid numbering system made ‘the future’ a far more comprehensible concept and enabled predictions to be made of what might happen and when. The system also suggested that the years would increase with no end, but later developments made the ideas of an apocalypse more tangible and suggested an end of the universe.

It is of the highest significance that our earliest historical apocalypses emerged within the Seleucid empire, within this world newly filled with inexorably increasing date numbers. These historical apocalypses are textual compositions that run through a full and extended account of world history, from the deep reaches of the past, through a succession of kingdoms or historical periods, into the Seleucid empire, and then to the predicted end of time itself. These works of end-time prediction do not appear before the Seleucid empire, such as in the Babylonian or Persian kingdoms or in classical Greek city-states. They do not appear outside the Seleucid empire, such as in the other Hellenistic kingdoms or at Rome. It is a phenomenon restricted to the Seleucid empire’s subject populations.

History appears here, perhaps for the first time, as a closed totality: ordered, whole, complete, head to toe.

So what of things like the Mayan calendars? Weren’t they more ancient? The article does not deal with this issue directly but this article says that the Mayan calendar was cyclical.

The Long Count is an astronomical calendar which is used to track longer periods of time. The Maya called it the “universal cycle.” Each such cycle is calculated to be 2,880,000 days long (about 7885 solar years). The Mayans believed that the universe is destroyed and then recreated at the start of each universal cycle.

So dates could be assigned within a cycle but did not continue across cycles. Within a long cycle, there were smaller units but not in terms of calendar years. The lack of a sequential numbering system within a cycle based on years made it more difficult to keep track of relative dates of events.


  1. Ken Baker says

    What is also interesting is, how did almost the entire world converge on a common 7-day week, so much so that saying today is Wednesday almost seems like an unchangeable natural phenomenon, like saying it’s now the Spring season in the northern hemisphere. You would think that some societies other than uncontacted primitive tribes would have arrived at a different length week with different day names, or simply not use a week at all.

  2. flex says

    @Ken Baker,

    The 7 day week is commonly assumed to be based on the lunar cycle of 4 moon phases (New, First Quarter, Full, Second Quarter), and each quarter of the 28 day lunar cycle takes 7 days.

    As the moon is visible to all inhabitants of the earth, and the 4 X 7 cycle is fairly easy to grasp, the expectation is that most (all that I know of) cultures created a 7 day week because of lunar cycles.

    There was much more difficulty in aligning the lunar 28-day monthly cycle with the solar 365+ day cycle. Many cultures simply gave up and had variable length holidays every year in order to get the lunar and solar calendars back into alignment.

  3. anat says

    flex, the lunar month, as observed from Earth, is not 28 days long, it is somewhere between 29 and 30 days long. Hence the length of months in those calendars that were based on observing the phases of the moon (such as the Jewish and Muslim calendars). So no, it is not trivial nor natural for humans to use a 7 day week.

  4. anat says

    See Babylonian calendar on the system the Babylonians used before the shift to 7 day weeks.

    There is also support there that the Sabbath was originally a monthly celebration (of the full moon) -- as can also be concluded from several mentions in the Bible’s Prophetic works, where the Sabbath is often mentioned together with ‘hodesh’ (ie month).

  5. benedic says

    Didn’t the PCE Greeks locate in time by using the number of the Olympiad.?

  6. flex says


    Each of the quarters lasts about 7.4 days, but can vary somewhat. Which is a close enough approximation for people to decide that 7 days makes a pretty good week. For people who are not tied too closely to a calendar, having to add a day or two occasionally isn’t a big deal.

    Then, as there are no direct records as to why a 7 day week was chosen, the best speculation I’ve seen has that it’s based on lunar cycles. Do you know of other cycles which occur in roughly 7 day patterns, and are short enough to be easily remembered (occurring in groups of 4)? The solar cycle certainly does not. Nor do any planetary cycles. I can’t think of any natural cycles which rigorously follow a 7 day (or multiple) period, at least any which seem more likely than lunar cycles.

    The human gestation period is occasionally brought up as a possible reason for a 7 day week. After all, it is approximately 40 weeks between the last menstruation and giving birth (with a wide amount of variation). But why would 40 be an important number to divide 280 days by to get seven? And until the relationship between menstruation birth was determined, it seems unlikely that women were counting in seven day blocks since their last menstruation.

    Further, we know from cave drawings that lunar cycles were being tracked as long as 25,000 years ago.

    I wouldn’t call it natural or trivial that this pattern was established, but I think it’s a reasonable inference that lunar observation by pre-historic humans led to a 7 day week.

  7. flex says


    Maybe we are talking across each other here, but the wiki article you pointed to about the Babylonian calendar appears to support my point about 7 day weeks being used. Including the occasional extra day thrown in to re-align those weeks to the lunar calendar, but that the 7 day weeks are based on lunar cycles.

    The lunation of 29 or 30 days basically contained three seven-day weeks, and a final week of eight or nine days inclusive, breaking the continuous seven-day cycle.[1]

    My bolding.

  8. anat says

    No it does not support that. They had ‘weeks’ of differing lengths because the lunar cycle is not 28 days but over 29.

  9. Tadas says

    My understanding was that the 7 days of the week came from the fact that there were 7 heavenly bodies that can be seen with the naked eye that traversed the sky unlike the stars. Sun. Moon. Mars. Mercury. Jupiter. Venus. Saturn. The roots of these words can be found in a mix of languages (Spanish and English for example). The sun is Sunday (the most important of the heavenly bodies and why it is associated with being a holy day in christianity for example). Lunes is the moon (obviously Monday). Martes is mars (tuesday). Miercoles is mercury (wed), jueves is Jupiter (Thursday), Viernes is Venus (Friday) and Saturn is Saturday. I suppose there was enough mystique behind these heavenly bodies that they were established into our calendar.

  10. consciousness razor says

    My understanding was that the 7 days of the week came from the fact that there were 7 heavenly bodies that can be seen with the naked eye that traversed the sky unlike the stars.

    Like flex was saying, it does seem like it spread from the Jewish and Babylonian traditions. I wouldn’t say it’s strictly about astronomical observations, since numerology also played a significant role. (Hard to separate the two, in that time period.) Why did everything come in 7s, not just in relation to the lunar phases but all sorts of things? I have no clue.
    It plays an analogous to the Roman 8-day week, or other “work” weeks or “market” weeks, which all constitute a relatively short period (not an annual/seasonal holiday or a few scattered intercalary days or whatever). The basic idea seems to be to specify a day (or days) which occurs fairly frequently (and regularly) and is set aside for worshiping, shopping, civic events, prohibiting certain activities that you’re superstitious about, or whatever your community may feel like doing with it. This is what the Sabbath is all about, and if it goes back to Genesis and Babylonian myths before that, it goes back a very long time.
    The idea of naming the days of the week after the (classical) “planets” is a separate issue. That was a later invention during the Roman Empire, many centuries after the 7-day week was first established (perhaps even 1000 years).

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