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All That Glitters, Experiment 3

A problem with finally picking up this blog a bit is that some of the old stories in it have been sitting idle for really quite some time. Does anyone remember, for example, that while I was working at the Barber Institute we got a small amount of money to zap gold coins with x-rays? If you do, you may remember that I’d already reported on the first two experiments we did in that project when everything here ground to a halt in 2016. Well, now I resume, with a brief account of the third experiment we did, and before long who knows, we may be through the rest!

Bruker S8 TIGER XRF analyser open for business

The S8TIGER WD-XRF spectrometer in the Department of Chemistry, University of Birmingham, with five sample cups waiting and one under analysis

A brief recap may be in order first of all, though. The very short version of the project’s purpose was: we had all seen an increasing amount of work using X-ray fluorescence spectrometry to analyse the fineness of precious-metal coins and sometimes even assign origins to its metal based on the trace elements therein. We had our doubts about this, but the manufacturers of some of the best machinery involved wanted to quell our doubts about this and offered us quite a lot of help with it, so we came up with a plan and, somewhat to our surprise, got both permission from the Henry Barber Trust to muck around with their coins and funding from the Royal Numismatic Society to do it, and so set about it. We began this in December 2014, with two experiments. The first was designed to test the viability of hand-held, portable, energy-dispersive machinery that could be brought to the coins; the second did comparator analyses using a fixed-location wavelength-dispersive spectrometer to which we had to bring the coins. This showed us that to detect anything at all of trace elements we would need the big machine, but also that it was picking up a whole load of stuff that seemed very likely to be extraneous material on the surface of the coins, probably from the soil in which they had long ago been found, rather than the stuff of which they were actually made. And that is about where we come in!

Gold solidus of Emperor Constantine VI and Empress Eirini struck at Constantinople 785-797, Barber Institute of Fine Arts B4599

The coin whose results (and details) are given in the first table below, set up for the test in which it did so

So, the third experiment was very simple. Using the same set of coins as we had previously run, I got hold of some conservation-quality acetone and a toothbrush, took them and the coins down to a workroom in the depths of the Barber and gave them all a careful but thorough scrubbing and let them dry, all except one that we left uncleaned as a check. Then I packed them up again and we bore them off to the Department of Chemistry on 22nd July 2015. There we ran them again, on the shorter of the big machine’s two cycles, and this gave us some results both before and after cleaning.

Unfortunately, if anything, the post-cleaning results showed more extraneous grot. That ‘if anything’ will tell you, though, that consistency was hard to observe. The variation wasn’t vast amounts, you understand, between half and one-and-a-half per cent, but cumulatively certainly enough to push our figures for the actual gold content up or down by two or three per cent, which would for some people be enough on which to found a theory about debasement… Here are the top ten elemental results from just one side of one coin by way of example:

Coin 170 (obverse)1 Percentage observed first time Percentage observed second time
Gold 86.51% 84.49%
Silicon 3.44% 4.63%
Silver 1.61% 1.43%
Aluminium 1.27% 1.19%
Potassium 0.80% 0.63%
Sodium 0.74%
Copper 0.44% 0.34%
Calcium 0.32% 1.96%
Sulphur 0.28% 0.48%
Iron 0.27% 0.50%
Total percentage of coin observed 96.38% 96.70%

Down by two per cent gold, and that mostly gone to silicon and calcium, even though some other small elements had dropped in the readings as well. Also, what this arrangement doesn’t show, the second time small but possible readings showed up for chlorine, magnesium and, way down the scale, platinum, all absent the first time through. Surely cleaning with acetone couldn’t have added calcium to the coin? But each coin we ran had its own little tale of additional mess to tell, even (and this should have told us something) the uncleaned check. Here are its top-ten figures for the obverse:

Coin 21 (obverse)2 Percentage observed first time Percentage observed second time
Gold 82.57% 87.43%
Silicon 1.82% 1.61%
Aluminium 1.01% 0.81%
Silver 0.74% 1.10%
Sodium 0.65%
Potassium 0.47%
Chlorine 0.45%
Calcium 0.44% 1.78%
Iron 0.31% 0.31%
Copper 0.24% 0.26%
Total percentage of coin observed 89.12% 93.80%

Some things are beguilingly similar, yes—iron and copper levels stay about the same—but others are not. The first test picked up sodium, potassium and chlorine but none of those turned up second time even though we’d actually got better readings with more of the sample observed (possibly because we gave it a flatter bit to look at). Were we just looking at a different bit? If so, that bit apparently had less silicon in it, but a whole whack more calcium in it. What can you do with these sorts of data?

Gold solidus of Emperor Anastasius I struck at Constantinople 491-518, Barber Institute of Fine Arts B0006, in an WD-XRF sample cup

The uncleaned check likewise set up for the results above, though I have to say it’s not like it looks dirty

So this was somewhat daunting, especially as we had four solid days of testing booked in for the following week and now somewhat less certainty that it would produce anything. At the time, my best guess was that the acetone had removed only handling patina, thus exposing the actual surface of the coin and everything that had adhered to or reacted into it while it was in the ground. Actually, looking back, I think we were already seeing here the conclusion that the final experiment would necessarily lead us to. But that would be getting ahead of the story, and even though this story is so very far behind, I have hopes of telling it as I wanted to anyway. So, till next post but, er, two, if I have my plans right (and no-one else dies—did you see Mark E. Smith has left us for the bar of the great and final WMC since the last post?), I shall leave the question hanging…

1. We used randomly-allocated running numbers throughout these experiments, so that we couldn’t try and guess what the results should be according to where the coins fitted in Byzantine history (or the previous curves laid down by work like Cécile Morrisson, Jean-Nöel Barrandon and Jean Poirier, “La monnaie d’or byzantine à Constantinople : purification et modes d’altérations (491-1354)” in Morrisson, Claude Brenot, Barrandon, Poirier and Robert Halleux (edd.), L’or monnayé I : purification et altérations de Rome à Byzance, Cahiers Ernest Babelon 2 (Paris: C. N. R. S. 1985), pp. 113–187. This one was actually Birmingham, Barber Institute of Fine Arts B4599, a solidus of Emperor Constantine VI and Empress Eirini struck at Constantinople between 785 and 797, online here. I’m actually almost loath to identify the coins here, though, lest it be thought I’m actually publishing figures for their metal content. As is probably clear, though, that’s something I’m sure we weren’t reliably getting.

2. And this one was Barber Institute of Fine Arts B0006, a solidus of Emperor Anastasius I struck at Constantinople between 491 and 518, online here, with the same reservations as in the previous note.


All That Glitters, Experiment 2

Somehow my posts about me and my work—and that may not be what you’re here for but, you know, I like it—have got behind my seminar reports in such a way that they’re into February 2015 and I’m still in December 2014. Let me resolve some of that disparity by giving you a short report on the second day of experiments in the collaborative project I’m in for analysing Byzantine gold coinage by X-ray fluorescence, which was 14th December. (If you need background I announced this project ages ago here and dealt with some of our starting questions and the first day’s experiment here.)

Cover of J. O. Jeppson, The Second Experiment

Our results have so far not been this dramatic, but then, I’m guessing that our first experiment wasn’t quite as adventurous as this must have been

To recap, we had established that if our experiments were to tell us anything much about elements other than gold, silver, copper and maybe one or two other pre-determined elements, we were going to need not the energy-dispersive machinery we’d been using on the first day but the bigger, more expensive and, most importantly, immobile wavelength-dispersive machinery in the Department of Chemistry in the University of Birmingham, a machine called the S8 TIGER. I am only just able to describe the difference between these two analytic methods: in so far as I can, it’s to do with what is being used to pick up the energy given off by the things you’re bombarding with x-rays. The WD machinery includes crystal collimators that are sensitive to certain wavelenths of that energy, which therefore get picked up better, where the ED machines, which measure only in terms of intensity of signal, simply wouldn’t see such things among the massive gold return, as we had surmised. The WD machine also scans its samples in a vacuum, which eliminates interference from the air.

Bruker S8 TIGER XRF analyser open for business

The mouth of the TIGER yawning wide, with five sample cups waiting and one under analysis

On the other hand there are also problems with the WD machinery that don’t exist with the ED kit. For us the first of those was simply access; it’s nothing to do with the actual machinery except in so far as it’s immovable, but because we had to take the coins to the kit rather than vice versa, that meant arranging transport and insurance even on campus, and the transport repeatedly went wrong, which cut into our experimental time a lot. But, also, the ED kit works with narrow beams focussed on points; the WD machine scans its samples in masks such as the one below, of which the two sizes relevant to us were 5 mm and 8 mm, and those were therefore the only area sizes that we could analyse. Importantly, this also precluded examining coins at their edges or over piercings, because the sample has to fill the exposed area completely. This also highlights a problem with both ED and WD methods: non-homogeneity. If for some reason your coin had an odd tiny lump of platinum on its surface, say, the ED machinery would either miss it (in which case you’d never know) or find it and report a massive platinum signal (which would be misleading for the coin’s overall composition). The WD machinery, however, would factor it into the average, so that you wouldn’t necessarily realise that it was a coherent inclusion rather than a component of the main alloy. So there was plenty to worry about even if the machine worked perfectly.

Emperor Heraclius just visible on one of his solidi of Constantinople loaded behind an 8 mm mask for analysis in the Bruker S8 TIGER

Emperor Heraclius just visible on one of his solidi of Constantinople loaded behind an 8 mm mask for analysis

Anyway, we had our goals clear for this test. The first was to get our hands on the machinery and find out what the operational considerations in any further planning were, the results of which you sort of see in the musings above. Here I have to acknowledge the tremendous help and general goodwill of Dr Jackie Deans, official keeper of the TIGER, and Dr Adrian Wright, who had first let us involve the Department of Chemistry in the project and had helpful things to say whenever he dropped in. Our second priority was to run the same ten coins around which we’d built our first experiment on the S8 TIGER and see how the results differed from those on the ED kit. And as it turned out, our third one was to determine how we wanted to use the S8 TIGER, because as Jackie explained to us, it could analyse at three levels, a 2-minute cycle that would probably get us no more data than the ED machinery had, an 8-minute one which should do the job, and an 18-minute one which was the very most data it could gather. Adding 10 minutes to each analysis was obviously going to limit the number of coins we could actually analyse in any given timeframe, so we really rather needed to know whether or not it was worthwhile.

Gold solidus of Empress Eirini at Constantinople set up for analysis in a Bruker S8 TIGER XRF analyser

The rather different visage in gold of the Empress Eirini, likewise cruelly cut down to 8 mm of glaring royalty

And so what did we find? Well, this machine certainly had more to tell us. We were now getting returns in terms of many elements, at concentrations of down to parts per thousand or even less. This ineluctably meant a decrease in gold concentration reported, because there was now simply more data to fit into the percentages, but the overall picture of lots of gold, not much silver and less copper was still very apparent in the reported figures. What we hadn’t expected, and had now to deal with, was that copper wasn’t usually the third most detected element, and sometimes silver not the second: instead, we were seeing lots of calcium, silicon and sometimes aluminium beating them out. It seemed a priori unlikely that these were original metallic components of the coins in these quantities. That in turn implied that these elements had got into, or much more likely onto, the coins since striking, be that from use, preservation or anything else that might have happened to them. But, whatever they were, they also seemed to be more consistently detected on the long cycle than the medium-length one, meaning that we were going to need to use the long analysis to have any chance of consistent findings. So now we had two difficult questions to answer in setting up Experiment 3: firstly, what could we get done with less than half the scans that we might have hoped to do in any given day of experiments, but secondly, when we did, could we determine whether these results were merely contamination or do anything about that if they were? And these were things which we attempted to address in the New Year, so I’ll stop here for now.

All That Glitters, Experiment 1

Almost the last academic thing I did last year before breaking for Christmas was the first two sessions of a project that is now nearly finished, All That Glitters, announced here so long ago. It was so long ago that it might be worth reintroducing. Basically, by great happenstance one of my predecessors in taking care of the coin collection at the Barber Institute had run into two people at a conference who were presenting about the ability of the X-ray fluorescence (XRF) equipment their company, Bruker Industries Ltd., produced to do metal analyses. That predecessor, Rebecca Darley, also knew Robert Bracey at the British Museum, who had done work with XRF on the coinage of the Kushan Empire, and now I was in charge of the Barber’s coins. None of us are archæometallurgists and our knowledge of archæology and numismatics didn’t necessarily combine with the metals analysis expertise upon which we could call so as to somehow make a composite archæometallurgist out of us all, but Robert could borrow the British Museum’s handheld XRF scanner, Bruker had a new machine they wanted to test against real problems, the Barber is on the same campus as several much larger and more expensive machines also supplied by Bruker some of whose host departments proved happy to let us use them and to tell us about them; a project seemed obviously to exist in potentio and our task was to work out how to make it tell us something useful.

Bruker Industries Tracer IV handheld XRF analysis system

I’m not sure if this is the exact machine we were using but its resemblance to a phaser seems impressively reminiscent

It’s too early to say whether we achieved that, pending actual publication of our results and conclusions which we are even now working on writing up, but right from the beginning it was clear to us that before we could have any historical conclusions we would have to have methodological ones. This is because there are so many potential problems with XRF analysis, problems which not all publications using it consider, and when they do, consider most often for silver alloys rather than the high-purity gold we would be testing, that the first priority had to be not to find things out, but rather to find out what we could find out.1 Accordingly, our pilot experiments were designed to evaluate the machinery more than the coinage, and we started on the 3rd December 2014 when Robert brought the British Museum’s handheld scanner up from the British Museum, along with its calibration standard, and Mike Dobby and Colin Slater from Bruker brought in their new M1ORA energy-dispersive scanner and we put some coins through their x-rays.

A gold solidus of Emperor Anastasius I struck at Constantinople (in the Eta <i>officina</i>) between 492 and 507, Barber Institute of Fine Arts B0005

The first coin to go under, a gold solidus of Emperor Anastasius I struck at Constantinople (in the Eta officina) between 492 and 507, Barber Institute of Fine Arts B0005

We had chosen a test set of ten coins running from Anastasius I (491-518) to Constantine VI (785-797), with two coins for each ruler from the same mint and if possible, the same workshop of the mint (if that’s what officinae were), hoping that whatever results we might obtain would thus be internally secure against outlier coins from a bad day at the mint or similar.2 All of those got zapped on both sides with both handheld and the microwave-like M1ORA. Both of these use a spot beam, but with the M1ORA it’s possible to target it precisely, so we aimed for flat surfaces wherever possible.

Bruker Industries M1ORA XRF analyser at work in the Coin Study Room of the Barber Institute of Fine Arts, University of Birmingham

The M1ORA at work in the Barber’s Coin Study Room, with team members in eager attendance

The initial results of this made the handheld device look like much the poorer sibling, as its readings were extremely variable. Robert worked out, however, that this was related to how much of its expected sample it had been able to observe—this in turn probably down to surface relief but already we were into unknowns—and when the figures were all normalised to a notional 100% of sample they came out much more like what the M1ORA was seeing. The M1ORA was able to dump its readings straight into a laptop equipped with suitable software, and did this levelling-up in that software, so made things immediately clearer for us by automating that step, solely an issue of configuration but we still needed to be aware of it. I keep stressing variables and difficulties because I don’t want to imply that we were getting actual true results, but that said, once they were both talking to us in the same framework the message of the machines was pretty consistent: all these coins were being analysed as very high-purity gold, 97% or more, which is astonishingly high for any pre-modern metallurgy. However, other than silver and copper, which occurred in about the proportions one would expect (i. e. not very much and even less), the only other element that was consistently detectable was iron. That was in part a factor of what we had asked Mike and Colin to make the machinery look for but if you have to do that at all, there is obviously a restriction inherent in your question-setting…

A gold dinar of Sindh imitating a Persian dinar of Shah Shapur II (309-379), struck at an unknown mint and date, Barber Institute of Fine Arts S0073

So then for something rather different, a gold dinar of Sindh imitating a Persian dinar of Shah Shapur II (309-379), struck at an unknown mint and date, Barber Institute of Fine Arts S0073

The very high fineness was sort of what we might have expected, anyway, as it is roughly what earlier analyses of Byzantine gold coins by a number of methods have suggested.3 It still made me uncomfortable for its lack of variety, however, and so since we had run-time left in the day I started hauling other things out of the cabinets. These included two Persian gold dinars, of Shahs Shapur II (309-379) and Varhran IV (388-399), and the above piece which is pretending to be something like the former, as well as an Arab-Byzantine solidus from Carthage and some more Byzantine pieces. Mainly I just wanted to be sure that the machinery actually would report lower gold finenesses, and so it duly did, with the Persian pieces both lower (but not by the same amount) and the Sindh piece even less fine (which, to be honest, was already apparent in its colour, but that was why I’d chosen it). The Byzantine stuff, and the coins imitating that, remained high in the machinery’s estimation.

A gold solidus of the second reign of Emperor Justinian II, struck at Constantinople between 705 and 711, Barber Institute of Fine Arts B4464

Another part of the starting sample, a gold solidus of the second reign of Emperor Justinian II, struck at Constantinople between 705 and 711, Barber Institute of Fine Arts B4464

This bit was fairly unsystematic sampling, but it did give us some reason to believe that the machinery was observing something consistent with our expectations, and which therefore fitted into existing understandings of the early Byzantine gold coinage. That is circular, though, obviously! This and the likely effect on the readings of differences between the surface of the coins and their cores, because of both manufacturing factors and subsequent environmental exposure, meant that we weren’t willing (and still aren’t) to say that these figures are actually how fine those coins were. We also weren’t seeing a range of trace elements which we had expected on the basis of older work, and which might have suggested things about changes in metal supply and treatment that would potentially be historical evidence.4 So, while these machines might serve other people’s purposes, we ourselves were going to need some bigger kit. And that would be Experiment 2, about which I shall write in a couple of posts’ time. In the meantime, however, here is some shiny metallic blogging for the Christmas season and I wish you all a happy holiday!

1. Part of our problem was that so much of the literature about these problems was old enough to relate, potentially, only to a much more primitive incarnation of the technique. Nonetheless, Michael F. Hendy & J. A. Charles, “The Production Techniques, Silver Content and Circulation History of the Twelfth-Century Byzantine Silver Trachy” in Archaeometry Vol. 12 (Oxford 1970), pp. 13-21, William A. Oddy, “The Analysis of Gold Coins—A Comparison of Results Obtained by Non-Destructive Methods”, ibid. Vol. 14 (1972), pp. 109-117 and J. Tate, “Some Problems in Analysing Museum Material by Nondestructive Surface Sensitive Techniques” in Nuclear Instruments and Methods in Physics Research Part B Vol. 14 (Amsterdam 1986), pp. 20-23, all suggest that differences should be observable between surfaces and cores of coins and between methods that measure only the surface and those that measure total composition, and L. Beck, S. Bosonnet, S. Réveillon, D. Eliot & F. Pilon, “Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques”, ibid. Part B Vol. 226 (2004), pp. 153-162, DOI: 10.1016/j.nimb.2004.06.044 and Vasiliki Kantarelou, Francisco José Ager, Despoina Eugenidou, Francisca Chaves, Alexandros Andreou, Elena Kontou, Niki Katsikosta, Miguel Angel Respaldiza, Patrizia Serafin, Dimosthenis Sokaras, Charalambos Zarkadas, Kyriaki Polikreti & Andreas Germanos Karydas, “X-ray Fluorescence analytical criteria to assess the fineness of ancient silver coins: application on Ptolemaic coinage” in Spectrochimica Acta Part B Vol. 66 (Amsterdam 2011), pp. 681-690, DOI: 10.1016/j.sab.2011.08.001, give some explanations of why that should be so. (I have to thank Dr Eleanor Blakelock for some of these and several other useful references.) All of these except Oddy and Tate were working with silver alloyed with base metal, however, and so another of the problems we have is in knowing how far the same applies to gold and if it does, whether if alloyed with base metals only or also with noble metals such as we expected to see. And the mess only gets worse from there…

2. Barber Institute of Fine Arts B0005 & B0006 (Anastasius I, Constantinople, officinae Eta and Iota), B2761 & B2762 (Heraclius, Constantinople, both officina Eta), B4384 & B4385 (first reign of Justinian II, Constantinople, former marked Theta), B4464 & B4465 (second reign of Justinian II, Constantinople, no control marks), B4598 & B4599 (Constantine VI and Eirini, Constantinople, no control marks).

3. Those earlier analyses being principally those gathered and conducted in Cécile Morrisson, Jean-Noël Barrandon & Jacques Poirier, “La monnaie d’or byzantine à Constantinople : purification et modes d’altérations (491-1354)” in Morrisson, Claude Brenot, Jean-Pierre Callu, Barrandon, Poirier & Robert Halleux, L’or monnayé I : purification et altérations de Rome à Byzance, Cahiers Ernest Babelon 2 (Paris 1985), pp. 113-187.

4. The kind of conclusions, indeed, that were coming out of ibid. and another study there, Jean-Pierre Callu, Claude Brenot, Jean-Noël Barrandon and Jacques Poirier, ‘”Aureus obryziacus”‘, ibid. pp. 81-111, albeit with a rather more variable sample of evidence!

Announcing All That Glitters

Starting work at the Barber Institute in August meant learning to work in and outside of office hours again, and I’m still rebalancing my routine. It has also meant an even longer to-do list, not least since I am also still doing some teaching for History at Birmingham on my spare day. There are long and difficult jobs connected with the electronic catalogue of the coins and the numismatic library, as well as more immediate ones connected with the next exhibition. But it has also meant a bunch of exciting new research projects! In some ways this should have been expected, and indeed I came into the job with one particular problem I wanted to use the coin collection to address, which I’ll tell you about when I’m slightly further along. But in the meantime, we are about to start something quite big and I wanted to announce it. The project name is “All that Glitters: the Byzantine solidus 307-1092″, and it aims to carry out non-destructive scientific testing of the metal composition of the Byzantine gold coinage over that period, up to 300 coins in all depending on results.

A gold solidus of Emperor Anastasius (491-518) struck in Constantinople, Barber Institute of Fine Arts B0031

A gold solidus of Emperor Anastasius (491-518) struck in Constantinople, Barber Institute of Fine Arts B0031

The reason this has got so ambitious is that word ‘we’, because this is essentially the brainchild of Rebecca Darley, one of the curators of the current coin exhibition at the Barber as you may remember and now part of the Bilderfahrzeuge project based at the Warburg Institute in London. Rebecca is an energising collaborator who does not think small and has thus gathered me, as the man with the coins and the wider medieval background, and Robert Bracey of the British Museum, as a man with an X-ray flourescence spectrometer and experience using it on the money of ancient empires, into a suddenly-active attempt involving Birmingham University’s School of Chemistry and Bruker Industries Ltd., who make XRF machinery among many other things, to deepen the basis of Byzantine monetary history (and with that, it’s probably not too much to say, the monetary history of the early Middle Ages as a whole). Here is our synopsis, with some edits for context:

“The Byzantine Empire, which evolved from the eastern Roman Empire, issued coinage continuously for more than a thousand years. The gold solidus, a coin of 4·5 g and a notional 95-97% purity, was the backbone of this system from the reign of Emperor Constantine I (306-37) to the eleventh century, though it was debased steadily from the tenth century until its replacement in a coinage reform in 1092. Before that time, the reputation of the solidus was near-legendary and it has remained so in scholarship.” In fact, however, we have limited evidence as to the precise purity or composition of the early coinage prior to debasement.
Earlier metallurgical studies of Byzantine gold coinages concentrated mainly on the later period, and used the most sophisticated equipment available in the 1980s and 1990s. Recent developments in X-Ray Flourescence technology, in which Bruker Industries Ltd. have been at the forefront, now make it possible to evaluate non-destructively the composition of metal alloys with far greater sensitivity to a range of trace elements, and the ability to quantify very small changes in the proportions of different metals in an alloy and in detecting and identifying even minute quantities of trace elements. “These newly developed techniques have not, however, been applied to Byzantine gold coinage and the time is therefore ripe for a project which could not only offer new data on the Byzantine monetary economy but also explore the possibilities of XRF testing, and set standards of analysis for other currencies and precious-metal objects.
“The Barber Institute of Fine Arts contains the most important collection of Byzantine coins in Europe and its greatest strength is in the coinage of the sixth to eighth centuries. It is currently unpublished, though cataloguing is in progress, and it has never been subject to any metallurgic analysis. It therefore offers an entirely new source of data for a detailed examination of the gold coinage that underpinned the Byzantine economy. In light of increasing recognition by historians that the numerous crises experienced by the Empire were survived only because of the sophistication and resilience of the imperial monetary and taxation system (Haldon, 1990; Wickham, 2005; Brubaker and Haldon, 2011), this study has immediate relevance not just to the Middle Ages but also to wider questions about the impact of monetary stability on political balance.”

You see that we have plans, and as of last week, we now have permission from the Henry Barber Trust, who own the collections of the Barber Institute, to carry on and do Science! with their coins. At this point we’re still in meetings-and-planning stages but before the end of the year we will in fact be zapping solidi with X-rays and trying to get money from people to do so on a rather larger scale. We should be presenting preliminary results from the first phase of work as early as January. It’s all moving rather fast! Anyway. One of our pledges is to keep the world updated via our various blogs, but I rather thought you might be interested anyway. Now, when those results come in, you’ll have some idea of what they might lead to…

The references above decode as John Haldon, Byzantium in the Seventh Century (Cambridge 1990); Chris Wickham, Framing the Early Middle Ages: Europe and the Mediterranean 400-800 (Oxford 2005); and Leslie Brubaker & John Haldon, Byzantium in the Iconoclast Era c. 680-850: a history (Cambridge 2011). To those I should add the essential starting point for the scientific study of Byzantine coinage till now, Cécile Morrisson, C. Brenot, J. N. Barrandon, J. P. Callu, J. Poirier & R. Halleux, L’or monnayé I : Purification et altérations de Rome à Byzance (Paris 1985).

Seminar CLXXXV: checking what the genes mean

The week after the seminar just reported, I was back down at the Institute of Historical Research’s Earlier Middle Ages Seminar to hear no less a notable than Professor Patrick Geary of UCLA address us with the title “Preliminary Reflections on Genomic Evidence and Medieval Migration History”. Perhaps because I was only just out of Oxford at this point, I had all kinds of misgivings about this talk: other notable historians who’ve lately got into scientific methods have perhaps let enthusiasm outrun rigour, and the only previous time I’d seen Professor Geary talk I’d taken away what seems to have been a quite misleading impression. In fact, this talk was earnest, humble even, critical and very interesting.

Map of distribution of Y-haplogroups in modern European DNA samples

Map of distribution of Y-haplogroups in modern European DNA samples, source unclear

Professor Geary was introducing to us a seriously international collaborative project that seems to have no name, quite hard to do these days, but which is described on his web-pages as “Tracing Longobard Migration through DNA Analysis”. You can probably see immediately why my alarm bells were ringing: a lot of fashionable work has been done with DNA lately that hasn’t thought terribly hard about what the actual meaning of its data might be. Professor Geary took us through the immediate problems: if you are using the DNA of modern populations, then you are looking at the sum of their total genetic background, including not just the episode of change in which you as historian might be interested but everything before and since, including the Black Death, the Wars of Religion, Industrial Revolution, various kinds of diaspora, and ultimately every human population change since the Second Ice Age, so it too often becomes a matter of proving what we already wanted to believe rather than showing anything new.1 On the other hand, historical DNA is far harder to come by, rarely adequately preserved, usually only recoverable in either its mitochondrial components (which descend in the female line) or its Y-chromosomal components (which do so in the male line) but not both (or so he said) and still has the same back-history problem even if subsequent accretion can be eliminated. And of course, both of these approaches tell you only what the (successful) components of someone’s biological descent were, not what they thought they were or how they behaved. DNA is not, now that we’re out of the nineteenth century, much of a determinant of identity. So what on earth can we hope to show with it?

Supposedly 'Lombard' funerary goods from a burial at Hamburg-Marmstorf

Supposedly ‘Lombard’ funerary goods from a burial at Hamburg-Marmstorf. Photo by James Seakley [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Well, the answer is of course in comparison. We can, with adequate funerary archæology, hope to see change in the DNA record, and can get some idea of the size, gender and composition of the groups in movement in the so-called Age of Migrations. Checking these findings against texts, material culture and stable isotope analysis can then also give us some means of establishing whether culture or population change in any one correlates with change in any of the others, which is really quite important to do since so much of what is wrong with current work on migrations in any one of these genres of evidence is the assumption that it must do so.2 Already, at what was then an early stage of this project, Professor Geary’s colleagues sifting through data from recent excavations were getting results showing mixed populations in movement, ‘Lombard’ cemeteries that did not include just Lombards and so on, though there was not enough asked here about how the checking category was constituted, I think. It was easy to miss such things when the following example was of a cemetery in Thuringia where they had women buried with material culture kits usually held to signify Thuringian origins and ones betokening Saxon identification and found from the isotopic analysis that it was the Saxon ones who were local! Given that most of us would perhaps cynically have expected no correlations at all, or in the case of some perhaps hoped for positive ones, negative ones was not what was expected by anyone! So some synthesis of this project’s results should prove eye-opening for us all, but will hopefully also allow some actually founded generalisations about what, in fact, an early medieval migration might have been like to be in the middle of.

Artistic depiction of the Vandal army arriving in Carthage

Depiction of the Vandal army arriving in Carthage, apparently what the Deutsche Post still think that looked like

There were, as you might imagine, lots of questions, and this not least because the actual presentation was relatively short. Some of the questions seemed to be aimed to reassure the questioner that this work would not be bringing back the spectres of nineteenth-century racialism that Professor Geary has previously done so much to dispel, but he assured us that the wrong questions of that era would continue to go unanswered.3 Others were keen to be assured that this work would not, ultimately, be able to disprove migrations, those others having their book sales to think of after all.4 The most interesting questions however came from Dr Mark Thomas, responsible for some of the DNA work that Professor Geary had attacked, and who was clearly coming from a very different place to the rest of us that made me briefly sad I was no longer so close to scientists as I had once been, so as to debate it with them: he was out to argue that historians’ tendency to make models more complex ineluctably made them subjective and therefore biased, and that the only hope for such work is to generate simple models that can thus hope to escape the biases inherent in, for example, choosing ‘ethnic’ markers.

Fig. 3 from Thomas et al., "Evidence for an apartheid-like social structure in early Anglo-Saxon England"

I would feel better about his criticisms of historians did Thomas’s own work not include things like this graph, fig. 3 from his and others’ “Evidence for an apartheid-like social structure” cited below

This boiled down into the clearest two-cultures confrontation I’ve ever observed, Professor Geary wishing to abjure Occam’s Razor to describe a process we can see must have been incredibly varied and Dr Thomas obdurate that if we historians tried to find that variation in the scientific data all we would wind up doing was repeating the process of choosing the patterns we like best, because the results would be too diffuse to clearly prove anything. Either of them could have convinced me separately: put together, it made me suddenly wonder whether we weren’t here exactly at the point where what we can genuinely know starts to dissolve, and amid the general hope that we would know a lot more for Professor Geary and his colleagues’ project I thus took away a nagging reminder that in real terms we actually ‘know’ almost nothing about the past, which implies not least that convincing people with racist agendas that they’re wrong is going to be tricky. Still: since even hard science is finding out these days that data does not convince, I’m not sure that leaves us so much further apart after all…4

1. One example of such work used by Professor Geary was Mark G. Thomas, Michael P. H. Stumpf & Heinrich Härke, “Evidence for an apartheid-like social structure in Anglo-Saxon England” in Proceedings of the Royal Society B Vol. 273 no. 1601 (London 2006), pp. 2651-2657, DOI: 10.1098/rspb.2006.3627, a paper also criticised by Magistra from a mathematician’s point of view here, and this one was indubitably the most sharp critique just because, unknown to Professor Geary of course, its lead author was in the audience. Also singled out, however, were Cristian Capelli, Nicola Redhead, Julia K. Abernethy, Fiona Gratrix, James F. Wilson, Torolf Moen, Tor Hervig, Martin Richards, Michael P. H. Stumpf, Peter A. Underhill, Paul Bradshaw, Alom Shaha, Mark G. Thomas, Neal Bradman & David B. Goldstein, “A Y Chromosome Census of the British Isles” in Current Biology Vol. 13 (Amsterdam 2003), pp. 979-984, DOI: 10.1016/S0960-9822(03)00373-7 and most of all Peter Ralph & Graham Coop, “The Geography of Recent Genetic Ancestry across Europe” in Public Library of Science: Biology Vol. 11 (San Francisco 2013), e1001555, DOI: 10.1371/journal.pbio.1001555, this last for spotting Hunnic migration using modern state boundaries, uncontrolled dataset and strictly out-of-date scholarship with which to interpret, according at least to Professor Geary: the historical cites actually seem fairly up-to-date to me, but this is not a paper one can skim for solidity of interpretation, so I haven’t…

2. Isotopic work on other hand takes a particular joy in exploding everyone else’s ideas, e. g. Janet Montgomery, Jane A. Evans, Dominic Powlesland & Charlotte A. Roberts, “Continuity or colonization in Anglo-Saxon England? Isotope evidence for mobility, subsistence practice, and status at West Heslerton” in American Journal of Physical Anthropology Vol. 126 (Hoboken 2005), pp. 123-138, DOI: 10.1002/ajpa.20111, and it’s hard not to like it for that but it is still using one form of evidence to show a bigger condition, even if that condition is undefined free flow of movement.

3. Patrick J. Geary, The Myth of Nations: The Medieval Origins of Europe (Princeton 2003).

4. If this all leaves you wanting more, you may be pleased to know that Professor Geary has written what seems to be a short version of this paper as “Using Genetic Data to Revolutionalize Understanding of Migration History” in The Institute Letter Spring 2013 (Princeton 2013), web version here.

Next stop Iceland?

This post is about pre-Viking settlement in the North Atlantic, and here specifically the Faroe Islands. I originally stubbed this in September 2013, when I came across a relevant web report on Melissa Snell’s medieval history blog at About.com, but since that time it seems that they’ve stopped keeping archives over there, so that post is now gone. Actually this is good news, because it forced me to web-search out other reports, and the obvious one, on Nature World News, also includes a link to the actual article behind it all, so now I can write you something informed.1

View from the south-eastern extremity of Sandoy in the Faroe Islands, looking south down the chain

View from the south-eastern extremity of Sandoy in the Faroe Islands, looking south down the chain, and shamelessly plundered from a Faroes tourism site, linked through

The story is that new research proves that the Vikings were not the first colonisers of the Faroes. This, and the fact that this was being published in an geoscience rather than a specifically archæological or historical journal, gave me some faint worries about sensationalisation of research meant to prove other things, as we have seen here many times before, but in this case, as far as I can see, it’s the real deal. The team in question were doing a low-urgency rescue dig on a coastal site in danger of erosion at Á Sondum on the island of Sandoy in 2002 and 2006. The site had been dug once before in 1994 and had then shown a Viking longhouse at the bottom of its occupation sequence (which subsequently went all the way up to the 19th century, always on the same spot, not least, as the article says, because there just aren’t that many sensible places to put settlements on the Faroes).2 This time they located the long-house’s hearth, and then they kept going and found more beneath. It wasn’t much more, just peat ash with carbonised barley grains in it, but this is significant for two reasons: firstly, barley isn’t native to the Faroes, and secondly, peat-burning requires usually months of cutting, stacking and drying, and thus implies prolonged settlement, not just drop-in visits. And they duly had radio-carbon analysis done on the barley grains and got the figures you see below.

Calibration graph and stratigraphical context of the radio-carbon samples from Á Sondum, Sandoy

From Church, Arge, Edwards, Ascough, Bond, Cook, Dockrill, Dougmore, McGovern, Nesbitt & Simpson, “Vikings were not the first colonizers”, p. 230, larger version linked through

There are some things I don’t fully understand about this, mainly because to get these dates they used not individual samples but a combined sample, whose results were mathematically combined using a ‘weighted mean’. Well, weighted how? I feel we should be told more about this.3 Still, unless it was actually weighted outside the sample dates, which would be some strange new definition of ‘mean’ of which I was not previously aware, the results still seem fairly inarguable: two straigraphically separate episodes older than the Viking site by between half a century and three centuries. I feel that a mean critic might be able to handwave away the more recent result, given it was right under the hearth and the dates could just about overlap, but the older one is much harder to get around, which gives one that bit more confidence in the younger one.

A forbidding shoreline in South-Central Iceland

An even more forbidding shoreline in South-Central Iceland, apparently being slowly washed away by glacial outwash, as presented in Albert C. Hine, Jon Boothroyd & Dag Nummedal, “Glacial Outwash Plain Shoreline, South-Central Iceland”, Beach of the Month, Coastal Care 1st August 2013, linked through

So, OK, what does this all mean? Well, most obviously it means that someone was on Sandoy burning peat and scattering its ash on the shoreline well before the Vikings got there (and the study is extremely careful to emphasise that we have no idea who). What our authors are most excited about is that there were, previously, very small signs of pre-Viking occupation in the palaeobotanical record (which is to say, barley pollen had been found before in a hard-to-date but potentially early context4), and that having been able to pin it down with actual digging like this has big implications for other island chains where such out-of-place floral data has turned up but been dismissed. But it also made them think of what it makes me think of, which is an old question about whether anyone got to Iceland before the Vikings. There are stories about this in the texts, firstly bewildering seafaring fantasies like the Irish Navigatio Sanctio Brendani, in which Brendan and his monks find a series of fantastic islands in the Western Ocean while in search of Paradise, which they duly locate and are allowed to stop in for a bit before turning for home to spread the good word.5 Much effort has been spent on pinning actual Atlantic islands into his tale, but, to be cynical again, one might as well try the same exercise with The Voyage of the Dawn Treader, the islands are equally allegorical in both texts.6 But there is also the Íslendingabók of Ari Thorgillson, ‘The Book of the Icelanders’, in which Ari reports that the first Viking settlers on Iceland found white-clad men they called ‘papar’ there who fled before the Norsemen, leaving behind croziers and bells.7 That looks so like the kind of people St Brendan actually led that it’s usually been assumed these were Irish religious taking the spiritual exile thing unusually seriously. But there is no archæological evidence to show that Ari was doing anything more than making this up by extrapolation from stories about the Western Isles of Scotland or similar. The archæologists here are suitably cautious about fitting these older debates around their findings:

“Who were these earlier settlers, how many of them were there and where did they come from? Were they single ecclesiastical anchorites as described by Dicuil from Ireland, Late Iron Age groups of colonists from Atlantic Scotland or pre-Viking explorers from Scandinavia? Did they continue on to Iceland, or did the Faroes represent a temporary diasporal bottle-neck, requiring later Viking seafaring technology to be able to sail to Iceland and Greenland, and importantly to sail back? To answer these questions, more and better-preserved pre-Viking Faroese archaeological sites need to be identified, excavated and analysed.”8

To that, I would only say that the Vikings’ seafaring technology was perfected well before the Viking disapora started, so that might not be the significant limitation, but the Faroes radio-carbon dates are still very early and the authors’ caution here is absolutely commendable.9 What they do do, however, is establish an excellent idea of where to look for such remains in island contexts, and that gives me hope that Iceland might, indeed, be the next stop, just because it would be fun finally to have some kind of archæology to set against Ari’s stories. I’ll let the authors of the article have the last word, though, because they have bigger things in mind than my antiquarianism, and will myself just finish by saying that I wish all science publications with historical impact could manage it as well as these writers have:

“This detailed examination at the base of coastal erosion archaeological sections was successfully used to identify the first archaeological sites of Mesolithic date in the Western Isles of
Scotland. A similar palynological argument for early human settlement was proposed for the ‘invisible Mesolithic’ of the Western Isles, where small-scale clearance episodes evident in pre-Neolithic pollen sequences, coupled with a rise in microscopic charcoal, led researchers to suggest that hunter-gatherer fire ecology accounted for these disturbances, despite the lack of any Mesolithic archaeological sites in the island chain. In the Faroes and the Western Isles of Scotland, small-scale perturbations in pollen sequences were interpreted as ephemeral human occupation events in periods prior to the orthodox landnám [‘land-taking’] events attested by the substantial settlement record of structures, dating to the Viking and Neolithic periods respectively. In both cases, the palaeoecological interpretations were eventually proved to be correct on discovery of ephemeral archaeological remains of pre-landnám date at the base of large coastal erosion archaeological sections and this raises intriguing issues about perturbations in palaeoenvironmental sequences prior to orthodox landnám chronological horizons in other island systems elsewhere in the North Atlantic and across the world, as in the Pacific."10

1. Mike J. Church, Símun V. Arge, Kevin J. Edwards, Philippa L. Ascough, Julie M. Bond, Gordon T. Cook, Steve J. Dockrill, Andrew J. Dugmore, Thomas H. McGovern, Claire Nesbitt, Ian A. Simpson, “The Vikings were not the first colonizers of the Faroe Islands” in Quartnerary Science Reviews Vol. 77 (Amsterdam 2013), pp. 228-232, DOI: 10.1016/j.quascirev.2013.06.011. Assigning author order on that must have taken nearly as long as the project itself…

2. Ibid. pp. 228-230; the previous dig, led by the second author here, seems not to have been published.

3. Rather than tell us about it, they refer to two other studies, P. J. Ashmore, “Radiocarbon dating: avoiding errors by avoiding mixed samples” in Antiquity Vol. 73 (Edinburgh 1999), pp. 124-130, which you’ll notice is a vote against doing this, and Ascough, Cook & Dugmore, “North Atlantic marine 14C reservoir effects: Implications for late-Holocene chronological studies” in Quarternary Geochronology Vol. 4 (Amsterdam 2009), pp. 171-180, DOI: 10.1016/j.quageo.2008.12.002, which presumably isn’t.

4. Here they cite a whole rook of stuff, the most recent of which is K. J. Edwards & D. M. Borthwick, “The pollen content of so-called ‘ancient’ field systems in Suethuroy, Faroe Islands, and the question of cereal cultivation” in S.-A. Bengtson, P. C. Buckland, P. H. Enckell & A. M. Fosaa (edd.), Dorete – Her Book – Being a Tribute to Dorete Bloch and to Faroese Nature, Annales Societatis Scientiarum Færoensis, Supplementum LII (Tørshavn 2010), pp. 96-116.

5. I’m not sure what the preferred edition of the Navigatio is these days but in trying to find out I have found Guy Vincent (ed.), “Navigation de Saint Brendan : texte latin et traduction”, http://www.utqueant.org/net/doc.3.Bren.II.html, last modified 24th October 2005 as of 26th August 2014, which will probably do. There is a good English translation in J. F. Webb (transl.), Lives of the Saints (Harmondsworth 1965), pp. 31-68, repr. in D. H. Farmer (ed./transl.) & Webb (transl.), The Age of Bede (Harmondsworth 1983), pp. 231-267 even though the text is likely from a century after Bede.

6. There are various studies on the Atlantic world implied by the text in John W. De Courcy & David Sheehy (edd.), Atlantic Visions (Dun Laoghaire 2009), which I will admit straight up I have never seen but just now pulled out of a database; any other suggestions?

7. There seems to be an edition of Íslendingabók by Guðni Jónsson online here but I have no idea how good it is; again, any better references would be appreciated. The standard translation, Siân Grønlie (transl.), Íslendingabók; Kristni Saga. The Book of the Icelanders; The Story of the Conversion (London 2006), pp. 3-34, is online here in PDF.

8. Church, Arge, Edwards, Ascough, Bond, Cook, Dockrill, Dugmore, McGovern, Nesbitt & Simpson, “Vikings were not the first colonizers”, p. 231.

9. Jan Bill, “Ships and Seamanship” in Peter Sawyer (ed.), The Oxford Illustrated History of the Vikings (Oxford 1997), pp. 182-201.

10. Church, Arge, Edwards, Ascough, Bond, Cook, Dockrill, Dugmore, McGovern, Nesbitt & Simpson, “Vikings were not the first colonizers”, p. 231.

Volcanoes probably don’t explain everything

I have mirrored on my various computers a huge directory called ‘toread’, in which get stuffed willy-nilly the various PDFs of academic writing that I come across while out and about the net, and every now and then I make a short-lived assault on it. At the time of writing this had just brought me into contact with an unusual article from Speculum of 2007, in which notable medievalists Michael McCormick and Paul Edward Dutton team up with a climate scientist by the name of Paul Mayewski and ask, more or less, can we achieve anything like precision in assessing how the weather and changes in it affected the societies of the early Middle Ages?1 And this is a thing I care about, sort of, so it probably won’t surprise you to learn that I read this with a sharp eye and have an opinion about it.

The Icelandic volcano system of Eldgjá

The Icelandic volcano [Edit: system] of Eldgjá, blamed here for an eruption c. 939 on the basis of tephra analysis. “Eldgja” by Andreas TilleOwn work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

Firstly it needs to be stressed that this is not an article about climate change, per se, though there is a certain amount of that in it as background. Cautious work I’ve seen on climate change has stressed that while it deals in overall trends of up or down a degree or two, the actual experience of this would have been far less comprehensible because of a huge range of local and chronological variation. If, for example, the winter temperatures where you are range from -18° Celsius to 13° Celsius over ten years, when a century earlier it had been -13 to 18, then yes, the median drop is already pretty severe but perceiving the actual pattern in any of those ten-year slots is going to have been pretty difficult given that maybe one January all the rivers froze and then maybe four years later your vines grew a second harvest because it was so sunny.2 And this article is interested in that short-range variation, the experience of individual years.

Ice core SO4+ and Cl- time series covering the period A. D. 650–1050 and historically documented multiregional climate anomalies between 750 and 950

“Ice core SO44+ and Cl time series covering the period A.D. 650–1050 and historically documented multiregional climate anomalies between 750 and 950″, they say on p. 877

The way they take this on is relatively simple, though it must have required a lot of work: McCormick and Dutton, both of whom have pedigree in this kind of question, separately compiled lists from documents of especially extreme winters in the years 750-1000, while Mayewski pulled a huge dataset from a Greenland ice core extracted in the 1980s and went through it looking for spikes in the deposition of chemicals associated with volcanic eruptions, whose aerosol effects in blocking out sunlight and lowering temparatures the authors work hard to show are widely accepted in meteorology.3 Then they compared their findings, chucked out anything that wasn’t certain and still had nine episodes where the dates for bad winters in the documents married up closely with dates for volcanic deposits.

For me, a historian, the best parts of this article are the documentary extracts that make it clear what kind of consequences such weather could have and just how bad it could be. For example, read this, their summary of two probably-related chronicles from Constantinople about the winter of 763 to 764:4

“Some 2,000 kilometers to the southeast, a well-informed observer at Constantinople recorded that great and extremely bitter cold settled on the Byzantine Empire and the lands to the north, west… and east. The north coast of the Black Sea froze solid 100 Byzantine miles out from shore (157.4 km). The ice was reported to be 30 Byzantine ‘cubits’ deep, and people and animals could walk on it as on dry land. Drawing on the same lost written source, another contemporary, the patriarch of Constantinople, Nicephorus I, emphasized that it particularly affected the ‘hyperborean and northerly regions,’ as well as the many great rivers that lay north of the Black Sea. Twenty cubits of snow accumulated on top of the ice, making it very difficult to discern where land stopped and sea began, and the Black Sea became unnavigable. In February the ice began to break up and flow into the Bosporus, entirely blocking it. Theophanes’ account recalls how, as a child, the author (or his source’s author) went out on the ice with thirty other children and played on it and that some of his pets and other animals died. It was possible to walk all over the Bosporus around Constantinople and even cross to Asia on the ice. One huge iceberg crushed the wharf at the Acropolis, close to the tip of Constantinople’s peninsula, and another extremely large one hit the city wall, shaking it and the houses on the other side, before breaking into three large pieces; it was higher than the city walls. The terrified Constantinopolitans wondered what it could possibly portend.”

As well they might! And of course, all this matters a very great deal in a society where the principal source of wealth and indeed subsistence is agriculture. Firewood can’t be gathered, new crops can’t be planted or are blighted by the temperature, animals die, wine freezes in barrels and is ruined, famine is grimly sure to follow.5 There certainly should have been big consequences of this kind of climatic variation.

Manuscript illumination of Emperor Louis the Pious as a Roman-style 'miles christi', by Hraban Maur

Manuscript illumination of Emperor Louis the Pious as a Roman-style ‘miles christi’, by Hraban Maur, not visibly taking any responsibility for the climate. “Ludwik I Pobożny“. Licensed under Public domain via Wikimedia Commons.

The first problem, though, is that it’s very hard to determine these consequences in any consistent way. The article opens with the suggestion that the harsh winter of 763 caused King Pippin III of the Franks to suspend his campaign against Aquitaine; it very nearly closes by suggesting that the run of bad winters and harvests from 821 to 824 helped plunge the Frankish Empire into war. So hang on: are wars more or less likely when the winter’s bad? Presumably it depends on other factors. And so on. The one thing that seems pretty certain is that people would have read the bad weather as divine punishment for someone’s misdeeds, but recent work on Louis the Pious makes it more than clear that that could be seized on and used to political advantage; we just can’t agree on whose advantage it was to…6

Causation is one of the problems I have with this article, and in fact I sense that the authors did too. There are a lot of ideas put forth then qualified in the concluding section, as if one or other author was happier to hypothesize than their counterparts. They note that the Roman Empire suffered very few of these events till its closing centuries, but then immediately say, “few would maintain that volcanically caused climate anomalies determined the course of empires and civilization”. Much larger jumps out and back are visible here:7

“A child born in 765 could die at the ripe old age of fifty-five without having lived through such a winter. One born in 820 would experience five such crises in the same span. Charlemagne was more than vigorous and smart: he was, with respect to volcanic aerosols and rapid climate change, a very lucky ruler.  Not so his son Louis the Pious, who, perhaps not entirely  coincidentally, in August 822, after the terrible winter of 821–22, ostentatiously expiated before his assembled magnates his and his father’s sins. Unfortunately, his act of public  penance would have little effect on the volcanic aerosol that produced yet another terrible winter, famine, and disruption but a year later. The reigns of his sons Louis the German and Charles the Bald would suffer from three such bad climate years each; in between two of them, Louis invaded Charles’s kingdom.”

If I’d submitted that to a journal like this I’d almost have expected it to come back stamped with “CORRELATION DOES NOT EQUAL CAUSATION” and indeed, if this had gone to a science journal I feel sure this would have been redacted. “Perhaps not entirely coincidentally”? Come on… This doesn’t diminish the factuality of their observations, but it certainly does need to be carefully considered just what this data explains.

The paragraph quoted also exposes another problem with the method adopted. In terms of volcanic aerosols, yes, Charlemagne may have been lucky, but the ruler who lived through the famines of 792-793 and 806 might have been surprised to be told so.8 If volcanoes caused bad weather, they certainly didn’t cause all of it, nor even perhaps the worst of it. This is something the authors of this article willingly admit, not least because their proxy for volcanic activity is located to the west of the most likely volcanoes, in Iceland, and the area they’re studying is to the east, though the Gulf Stream makes that much less of an objection than it sounds.9 Nonetheless, when the recent ash-cloud closed the Atlantic to air travel, I personally didn’t notice any shortfall in local autumn apples in the UK, did you? And so on.

Map of volcanically-linked climate anomalies of the Frankish period with dates

Map of relevant events with dates from their p. 875

When one looks more closely at the chronology, in fact, this gets rather odder. There are acknowledged problems with the chronology here; the texts, though subjective, are at least reasonably chronologically precise, and it’s useful to see it all together, because it means that even when things with chronology as shaky as the Irish Annals are being deployed, they’re being correlated with unconnected texts that give one some confidence in the dates. Not so the ice-core, unfortunately; that was sampled every two and a half years and the possible error of each sample is somewhere between one and six years.10 When one notices, then, that the volcanic deposition evidence that correlates with the 763-4 ‘event’ came from the slice for 767, obviously that possible error is important; either the sample’s dating must be emended, or the bad weather was well in force before the volcano did its stuff. The authors seem too comfortable about this for my liking and I agree with them very much that it would be nice to get a new core with the more precise dating that is now possible.11 That would also refine cases like bad winters in 855-856 and 859-860 which correlate with deposition spikes in 854, 856 and 858. It does fit quite nicely but whether or not, as the authors prefer, this was one long volcanic event, the fact that it apparently got better in the middle again monkeys with any simple causation from volcanic eruption to economic and climatic distress. I do think this article shows that something was going on here that deserves to be considered, and I am myself still very much of the persuasion that such factors do need to be considered as explanations for social change, but despite the extra precision attempted here I still don’t think we have anything as simple as A causes B causes C here, and I don’t honestly see how we get it, however much the technology may improve.

1. Michael McCormick, Paul Edward Dutton & Paul A. Mayewski, “Volcanoes and the Climate Forcing of Carolingian Europe, A.D. 750–950” in Speculum Vol. 84 (Cambridge MA 2007), pp. 865-895.

2. There’s lots of examples of freezing rivers (and occasionally seas!) in the article; the second harvest of grapes is something that repeatedly comes up in Gregory of Tours’s Histories, though it’s never good: see Gregory of Tours, The History of the Franks, transl. Lewis Thorpe (Harmondsworth 1974, many reprints), VII.11 or IX.5.

3. McCormick’s and Dutton’s work on such matters is in fact encapsulated in the same volume, in the forms of M. McCormick, “Molecular Middle ages: early medieval economic history in the twenty-first century” and Paul Edward Dutton, “Observations on Early Medieval Weather in General, Bloody Rain in Particular”, both in Jennifer R. Davis & McCormick (edd.), The Long Morning of Medieval Europe: new directions in early medieval studies (Aldershot 2008), pp. 83-97 & 167-180 respectively. On the methodology, see McCormick, Dutton & Mayewski, “Volcanoes”, pp. 867-878 and esp. 876-878.

4. Ibid. pp. 880-881, citing “The Chronicle of Theophanes Confessor: Byzantine and Near Eastern History, A.D. 284–813, trans. Cyril A. Mango, Roger Scott, and Geoffrey Greatrex (Oxford, 1997), pp. 600–601″ and “Nikephoros, Patriarch of Constantinople, Short History 74, ed. and trans. Cyril Mango, Corpus Fontium Historiae Byzantinae 13 (Washington, D.C., 1990), pp. 144–49, here pp. 144, lines 1–16, and 147″, along with full edition refs for Theophanes and some discussion of the connection between the sources.

5. McCormick, Dutton & Mayewski, “Volcanoes”, and their refs at e. g. pp. 879 (blight), 882 (impossibility of planting), 883 (death of beasts), 885 (more blight and death of beasts, also freezing wine).

6. Ibid. p. 867 (“that surely explains the suspension of the major effort by the king to conquer Aquitaine the following summer”) cf. p. 892, quoted below; on debate over Louis the Pious see Heinrich Fichtenau, Das karolingische Imperium. Soziale und geistige Problematik eines Grossreiches (Zürich 1949), transl. Peter Munz as The Carolingian Empire (New York City 1954), Louis Halphen, Charlemagne et l’Empire Carolingien (Paris 1968), transl. as Charlemagne and the Carolingian Empire (Amsterdam 1977) or François-Louis Ganshof, “Louis the Pious reconsidered” in his The Carolingian Empire and the Frankish Monarchy (London 1971), pp. 261-272, versus the various studies in Peter Godman & Roger Collins (edd.), Charlemagne’s Heir: new perspectives on Louis the Pious (London 1990), especially Stuart Airlie’s and Janet Nelson’s.

7. McCormick, Dutton & Mayewski, “Volcanoes”, p. 892.

8. Adriaan Verhulst, The Carolingian Economy (Cambridge 2002), pp. 123-124.

9. McCormick, Dutton & Mayewski, “Volcanoes”, p. 869:

“Those same complexities mean that not every volcanic deposit in Greenland will translate directly into climate impact on the European continent, for instance, if an eruption occurred on Iceland at a moment when atypical atmospheric circulation conditions carried the aerosol westward toward Greenland.”

10. Ibid. pp. 869-870, inc. p. 869, authors’ emphasis:

“The maximum possible absolute dating error for our period in this core is approximately six years. However, within any section of the core, say 100–200 years, the relative internal error is much less, since absolute error accumulates with depth. The closer the annual layer is to a securely identified volcanic event, the more likely the error is zero.”

11. Expressed ibid. p. 891. I discovered after first drafting this a newer paper by one of the same authors and a bunch of others, Francis Ludlow, Alexander R. Stine, Paul Leahy, Enda Murphy, Paul A. Mayewski, David Taylor, James Killen, Michael G. L. Baillie, Mark Hennessy and Gerard Kiely, “Medieval Irish chronicles reveal persistent volcanic forcing of severe winter cold events, 431–1649 CE”, in Environment Research Letters Vol. 8 (Bristol 2013), pp. 24-35, doi:10.1088/1748-9326/8/2/024035, which takes the same essential data over a longer range, using however only the Irish Annals, excluding ‘unreliable’ events but not engaging at all with the difficulties of their year-by-year chronologies, and winds up essentially using those to add precision to dating of events from the same Greenland ice-core sample. I haven’t read this in detail, nor have I read much of the recent work by McCarthy on the Annals that they cite, but their approach to the texts makes me wince pre-emptively even so. Anyway, the article is Open access and can be found here, and it is picked up by the BBC here, bless them linking to the actual article unlike some, whence it was reported by via David Beard’s Archaeology in Europe where I read it, and to whom therefore a tip of the hat!