Dendro Dissidents

Afternoon tea with my friends Åke and Petra inspired me to re-run this post from March 2010. Professional dendrochronology is still almost entirely a black-box in-house endeavour, that is, it is still not great science. Field archaeologists: when you saw your wood samples for dendro, get two samples and send one to the amateur community! They practice open data sharing. Check out Åke & Petra’s web site!


How long ago was the time of Emperor Augustus? Most educated people, including professional historians and archaeologists, will reply “about 2000 years” if you ask them. But a considerable number of amateur dendrochronologists say “about 1800 years”. And because of an unfortunate peculiarity in how professional dendrochronologists work, it is very hard to convince these dissident amateurs that they are wrong. Because they’re actually thinking straight given the data available to them.

If you look at published dendro curves for the transalpine provinces of the Empire, you find that they contain two main blocks of information covering the past 2500 years or so. There’s one that extends solidly from today and back to about AD 400, consisting of many tightly interlinked samples. And then there’s a Roman-era block that is also quite solid internally. But between the two blocks is a period of about 200 years when there are very few samples. It appears to be hard to find preserved timber that grew in the 3rd and 4th centuries AD. There are enough samples to satisfy professionals that they actually have the whole 2000 years covered, but the sample overlaps for the gap between the blocks are few and rather weak.

Professional dendrochronologists explain this lack of finds by reference to the cessation of Roman building projects and to deforestation during the Imperial centuries. According to the accepted model, the reason that there are so few samples covering the gap between the blocks is that few trees were of a suitable age for construction timber during that time and even fewer were used to build anything that has been preserved. Trees that fell into bogs and rivers at the time would have too few rings to be of much use to dendrochronology.

Dissident amateurs instead think that the Roman block and the recent block have been joined incorrectly, and that there shouldn’t be any gap at all between them in the diagrams. According to them, the professionals have been fooled by the early historians Dionysius Exiguus and Beda Venerabilis into thinking that the Western Empire fell 1600 years ago, using this as an axiom in their work with the dendro curves, when in fact it happened only 1400 years ago. A common idea about why this should be so is that the Church of Rome added a couple of centuries to its age to gain legitimacy: in other words, a conspiracy of early historians.

I mentioned published dendro curves. The rub here is that most dendro data are never published. They are kept as in-house secrets in dendro labs in order for these to be able to sell their services to archaeologists. So when the amateurs challenge the professionals’ opinion, all the latter can reply is “We know we’re right but we can’t show you how we know”. And that is of course an unscientific approach to the issue. The amateurs rarely get access to 1st Millennium wood samples, and basically have to work with the past 1000 years in their own studies. And so they cultivate a dissident opinion that could swiftly be laid to rest — or be accepted as fact — if wood samples and measurement databases were only made public.

My guess, though, is that any Roman archaeologist could solve the controversy quite easily, perhaps even using published radiocarbon dates. All you need are a couple of well-sourced dates for contexts known to be from about the time of the first emperors, such as Pompeii. (But if you know that a context is from that time, then you have very little reason to pay for radiocarbon dating.) Because although the calibration curve for radiocarbon depends on dendrochronology, several of the available datasets are not from European wood samples. And there is of course no inherent bias about where on the diagram the fall of Rome should be in North American dendrochronology, for instance.

Author: Martin R

Dr. Martin Rundkvist is a Swedish archaeologist, journal editor, skeptic, atheist, lefty liberal, bookworm, boardgamer, geocacher and father of two.

28 thoughts on “Dendro Dissidents”

  1. According to them, the professionals have been fooled by the early historians Dionysius Exiguus and Beda Venerabilis into thinking that the Western Empire fell 1600 years ago, using this as an axiom in their work with the dendro curves, when in fact it happened only 1400 years ago.

    And what is their basis for this claim, apart from the issues with the gap in dendrochronology blocks?

    The Western Empire was still around in the early 400s. Rome did not fall until 476. The Eastern Empire remained until 1453. So there should be continuous written records over the period in question, and the existence of structures from the very late Western Empire is not ruled out (although there are probably not many of them).

    We also have independent means of determining certain dates, such as the Plinian eruption of Vesuvius, which buried Pompeii and Herculaneum in ash.

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  2. Erik, there are some spots in imperial Roman and early medieval history where the records are pretty thin, but I do not think there is room for 200 phantom years. You are right that Latin and Greek and Syriac and Armenian sources all cross-reference. Still, open data is important, and it would not be very hard for professional archaeologists to test the idea.

    I hope that one day they can extend the dendro record for the Eastern Mediterranean into the second millennium BCE and see if we have the right size of gap between the Amarna Age and the reappearance of good records in Mesopotamia. There was a recent article arguing that C14 data from Thessaly support the conventional dates for Mycenaean Greece, but more lines of evidence are always better.

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  3. I’ve ruined a brand-new Sandvik hardpoint slicing LN/Beaker age (mineralised) 200mm-plus oak posts on site, and after all that (an hour or more of, if I say it meself, time-served-tradesman sawing, I know what I’m about) the outer layers were too messed up to get a terminus-ante. And the inner curves or whatever don’t match available European ones for some reason. Then they lost it in the Unit rubbish-dump/post-ex “storage”, stored in a sweaty polyethylene builders’ sack, along with others holding heaps of unsieved quartzite debitage.
    Things that make you go .. Hmmm ..
    I has a sad :¬{

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  4. Martin’s blog item above is mostly based on what we knew in 2010. Since then we have found strong dendrochronological support for that wood of West-Roman archeological origin is generally dated 218 years too old. You get a quick overview if you read here:
    http://www.cybis.se/dendro/dendro-audit/
    and perhaps here:
    http://www.cybis.se/dendro/ancient-history/

    This also makes that the “Plinian eruption of Vesuvius, which buried Pompeii and Herculaneum in ash” (which Eric Lund refers to, normally attributed to AD 79), would have to be moved to the 4th century. Some kind of headache for the ice core people who use this date to calibrate the older part of their cores.

    But as one scientist pointed out: If you are right, then everybody else will be wrong. How can that be possible?

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  5. As a comment to “dustbubble”:
    If you have not read Torbjörn Axelsons article in “Fornvännen” in 2007, please do that. As Torbjörn put it:
    “No archeologist would accept sending his potsherds to an expert who returned a statement saying they were from this or that period and then let the potsherds disappear without further documentation and the possibility of a follow-up!”

    Here is an English version of Torbjörn’s article:
    http://www.cybis.se/dendro/how-to-guarantee/

    If you are yourself working a lot with wood, consider joining the group of amateur dendrochronologists. Crossdating is not difficult or expensive. Though you have to be careful in your job. – For data related to Scandinavia, you might find the references you need in our wiki at
    http://www.cybis.se/wiki/index.php?title=List_of_references_useful_in_southern_and_central_Scandinavia

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  6. Lars, your website talks about whether the Julian calendar at the time of the Council of Nicea contained the expected slippage from the way it was set up under Caesar. I wonder if the Romans might have continued to insert intercalendary days ad hoc as they did before Caesar’s reforms.

    I agree that dendrochronologists should show their data just like numismaticists will show serieses of coins bearing the names of early medieval rulers, or historians will show texts which date themselves by AD, consular, or regnal years.

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  7. Thanks Lars will do (too knackered tonight, from shovelling desperately ahead of looming hell-storm, after weeks of drought. Not archaeology, hence the exertion).

    Luckily it wasn’t my site. I was just a site ass’t.-type monkey, who didn’t throw a wobbly if presented with interminable and tedious “unarchaeological” drudgery, so all the delicate flowers were only too pleased to appeal to the boss get me to do crap jobs that none of them could do anyway (better than listening to their brain-crippling constant chit-chat, while being forced to kneel or crouch in close proximity to a herd of them for hours).
    Sodding site can record itself, obviously.
    Don’t care, still got paid (handsomely ;¬D )

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  8. Sean, there was indeed some trouble with the addition of leap years in the beginning, see http://en.wikipedia.org/wiki/Julian_calendar, “Leap year error”. But this error was so flagrant that it was detected and adjusted already under Augustus. So after AD4 the calendar was operated as Caesar intended, but or course: you never know …

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  9. Absence of evidence is not evidence of absence.

    The Greenland ice cores themselves provide some form of calibration. They record not only the Plinian eruption, but also a very high level of metal smelting activity during the Western Roman Empire which ceased with the collapse of the Empire, and was not equalled again until the Industrial Revolution. If there is not much wood available for the period 200 to 400 AD, it is probably because it was being burned to make charcoal for smelting, in addition to the obvious deforestation point.

    Then, of course, despite the ever-present blinkered Eurocentrics, there was another great civilisation which was flourishing during this period on the other side of the world but which was not totally isolated from Europe in terms of contacts – the Romans and the Chinese knew very well that each other existed. The Chinese had their own astronomy and calendars, and they show no evidence of this time gap at all.

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  10. John, very interesting indeed. Could you please give a reference to the article in which the Vesuvius is chemically identified as the source for the ice core ash layer assigned to AD 79? And another reference to the evaluation of metal levels in ice cores?

    Regarding your second point, I do not know if the Romans and Chinese had contacts with each other. What I know is that there is no time gap as time is continuous. We only postulate that the Romans flourished some 200 years later than assumed, based on dendrochronology.

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  11. I have read your papers and the referees’ comments on them. Frankly, you asking me for references here is a bit of a joke. As far as I can see, most of the referees were bending over backwards trying to be helpful to you, but you just took it as unhelpful rejection and dropped it.

    There were indirect contacts between the Romans and Chinese, but no less valid for the purpose of cross-calibration.

    What I am saying is that I think you are wrong just to take your own dendro analysis as evidence for a major time gap that no one else in this or any other field has detected, then challenge everyone to prove you wrong, and then just give up and drop it because what you have written is not immediately accepted for publication. If you are serious about this, you should have (i) taken the very good advice given by some of the referees, and (ii) looked at other sources for calibrating the timing of the Roman Empire, not just dendrochronology, which obviously has its weaknesses.

    To flourish this as a conspiracy by a few ancient geezers is really unconvincing and not good enough.

    That is my amateur opinion.

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  12. John, first you sprinkle around a lot of assertions and are not able to provide references for them.

    Then you pretend that you are able to judge that the referees are right and we are wrong.
    By the way: there is no major time gap, but there are a couple of major gaps in the dendro masters which are well known and acknowledged within the dendro community, which we have analyzed.

    And finally you refer to “other sources for calibrating the timing of the Roman Empire” without naming them.

    Not very scientific indeed.

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  13. Petra, as an ancient historian I would be surprised if we know that. I do not think that we have many sources from the early Roman empire which are geeky about the Julian calendar; papyri from Egypt might help but I do not know how many bear dates in the Roman system. Astronomers and religious minorities often used other systems.

    I think that the “Cambridge Economic History of the Greco-Roman World” has a citation to the ice-core data.

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  14. While trying to refresh my knowledge on Roman – Chinese relations I read a paper by Krisztina Hoppál: https://www.academia.edu/1945062/The_Roman_Empire_according_to_the_Ancient_Chinese_Sources

    There is little in Chinese records that can bind Chinese time to an event within the Roman Empire. It is not
    even clear if the description of the “capital of Daqin” refers to Rome, Konstatinopel or the Syrian Antioch

    A for us interesting point in this paper is the Roman time silk production. Hoppál writes: “the passage on silkworm breeding is still a disputed point of research …”

    Hoppál refers to five Chinese sources where three of them write about silk production in “Daqin”: the “Wei lüe” compiled before AD 297, the “Wei shu” refers to the period 386-556 and “Hou Han shu” whose author died in 445.

    According to a story by Procopius, it was not until 552 that the Byzantine emperor Justinian obtained the first silkworm eggs. http://en.wikipedia.org/wiki/History_of_silk#Silk_in_the_medieval_world

    In contrast to this, Pliny the Elder (dead AD79) gave a detailed report of silkworm raising on the island of Cos.
    A reasonable explanation is that Pliny referred to “Asyrian silk”, which originates from another type of silkworm than that used for silk production in China.
    After Pliny’s notation, there is no mention of silkworms in the Roman sources after the 1st century.

    Now if Chinese records from the period 290 – 550 all write about Roman time silk production then they refer to a production that is not mentioned in Roman time records after the 1st century.
    So the Chinese records (especially the two younger ones) seem to be based on somewhat obsolete information.
    Hoppál refers to some possible explanations for this.

    Though if Pliny the Elder died in AD 311 (instead of 79) and the Roman records ceased to mention silk production after AD 332 (instead of 100) then the Chinese records on Roman time silk production would look more “up to date”.

    For more stories in this category, see http://www.cybis.se/dendro/ancient-history/indications-for-timing-problems/

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  15. I could go on. And on. And on, almost endlessly, without touching on the literature which is not open access.

    I have to conclude that you are not aware of this evidence simply because you haven’t looked, or that you ignore it because it refutes your claim.

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  16. John, sorry but thing appear being not so easy …

    Our papers concentrate on dendrochronology only, as dendrochronology is our expert discipline. However, on our web site we discuss other supporting evidence like astronomy. And we also touch ice cores (http://www.cybis.se/dendro/dendro-audit), where we cite the Clim.Past article by Barbante et al. and also link to the interactive discussion which preceded the publication. Have a look at the comments, especially that of Mike Baillie. There is no proof that the features in the ice cores are from a Vesuvius eruption, and even less that it is the one of AD 79.

    If we are right, the eruption which killed Pliny would have been in AD 311, and the consensus ice core calibration would be very wrong. In that case a completely new calibration would be necessary before any relevant statements about metal smelting in historical contexts could be made.

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  17. It’s going to take a bit more than recalibration of some ice cores. I see you have already made a start on rewriting a bit of ancient history to make it fit. Anyway, good luck with that.

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  18. This seems a bit like the argument against evolution based on the lack of intermediate forms in the fossil record. Sometimes it pays to be guided by theory. One could have argued that Mendeleev’s periodic table was pure sophistry and that there was no such thing as eka-boron. At least one could have until the discovery of scandium. Until the 1960s, it was possible to argue that the moon only had one face as no one had seen the other.

    Ancient history is often spotty. There’s a whole blog trying to figure out Emperor Trajan who is noted for his lack of contemporary historical sources as well as his column and wall. He is 100 years too early for this tree ring gap, so he can’t account for the missing tree rings in question.

    Of course, this kind of thing has an entertainment value and attracts true believers. Look at the case of those who deny the existence of the American state of Missouri, ironically known as the “Show Me” state. http://www.patheos.com/blogs/slacktivist/2011/01/25/anti-missourian-best-sellers/

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  19. I worry about vertical smudging of the ash layers in the ice.
    — — — — — — — —
    I have always assumed the best way to unite “floating” dendro sequences is to buy a good underwater RV and pick up ten thousand logs from the anoxic bottom of the Black Sea.
    C14 dating plus identifying the isotope signature for the region where each grew will provide a neat dendro sequence for a big chunk of Europe and Asia Minor. No more guesswork.

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