A problem of concavity

Now that I am returned from all my conferences, I have a few very frantic months left as a numismatist before I demit that noble calling so as to return to medieval history of more traditional sorts. In fact, of course, I will not be leaving the coins completely behind me: almost the first thing I will be doing in my new rôle is to give a guest lecture back at the Barber Institute, as part of my own exhibition there, and then I’ll be going to the International Numismatic Congress in Taormina, and I should just be back from that in time to start teaching the aftermath of the end of Roman rule in the West. And in fact, even then, I shall have enough publication projects in hand what with All That Glitters and a couple of other things to do with the Barber’s collections that it may take a while for anyone to notice that coins are not, in fact, what I work on… In that spirit, therefore, here is something like an informal presentation of the problem my paper at Taormina will be addressing, which I do mainly so as to have a first go at posing the problem in text. Basically, my question is: why did Byzantine coins turn concave?

A tray full of pale gold and billon coins of Emperor Manuel I Komnenos (1143-1180) in the Barber Institute of Fine Arts, Barber Institute of Fine Arts B5704-B5735

A tray full of pale gold and billon coins of Emperor Manuel I Komnenos (1143-1180) in the Barber Institute of Fine Arts, all concave, Barber Institute of Fine Arts B5704-B5735

It is perfectly reasonable for your first reaction to this question to be “What?”, don’t worry. But this is a thing that happened: from the 1050s onwards, more or less the reign of Michael IV (1034-1041), Byzantine precious metal coinage began to be manufactured with a slight dish-shape that became more and more pronounced, and then spread to the lesser metals too. It also went badly downhill in metal quality, and by the reign of Emperor Alexios I Komnenos (1081-1118) the situation was so bad that despite the massive calls on his empire’s much-reduced resources he reset the coinage in the only way one really can in an international precious-metal economy, by accepting the degradation of the existing coins, reclassifying them and introducing a new, 80%-gold denomination, the hyperperon at the top of the tree.1 The old supposedly-gold nomismata became either electrum (gold-silver alloy) or billon (lightly-silvered copper) ‘trachies’, and this meant that the small change was also now concave, though there was also a flat bronze tetarteron that was used especially in what is now Greece.2 Anyway, I digress. The real question is, why adopt the dished design anyway?

A billon trachy of Emperor Alexios I Komnenos, struck at Constantinople in 1092-1118, Barber Institute of Fine Arts B5558

A billon trachy of Emperor Alexios I Komnenos, struck at Constantinople in 1092-1118, Barber Institute of Fine Arts B5558

One thing, and really one thing only is sure about this, which is that it was not an easy thing to do. In the first place, the designs on the dies with which the blank coins were struck were carved in such a way as to keep the design correctly proportioned: it looks straight even though it’s bent, something that becomes very evident when you try to photograph them in such a way that they face you but are still clearly concave. Scanning is better for this because the fall of light emphasises shadow, but with adequate lighting the concavity is quite often visually undetectable in conventional photography. So that was cunning artistry, and not least because the dies themselves, we are fairly sure, were made curved, rather than deforming flat coins by striking them.3 In fact, it seems likely that the flat blanks were first struck with blank dies to curve them, and then the resulting curved blanks were struck with two obverse dies, one for each side of the coin’s design, to ensure a good impression all over the coin’s surface.4 This means that the manufacturers were readier to triple the production process complexity than to make dies that fitted each other snugly, apparently, but we can mainly take from this: there must have been a point to all this, but what?

Electrum nomisma histamenon of Emperor Alexios I Komnenos, struck at Constantinople in 1081-1092, Barber Institute of Fine Arts B5224

Electrum nomisma histamenon of Emperor Alexios I Komnenos, struck at Constantinople in 1081-1092, Barber Institute of Fine Arts B5224

None of the existing ideas seem very satisfactory. They are, roughly:

  1. it made the coins stronger, preventing them snapping;
  2. it made the metal quality of the coins more evident, reassuring people that they were good;
  3. it made the coins stackable in a way that the relatively high-relief flat ones were not;
  4. it brought coins whose low standard had made them much bigger than the older solidi with which they were notionally interchangeable, because gold is denser than anything it might be replaced with, back down to a more acceptable width;
  5. it made the coins better to play tiddly-winks with.5

Now, don’t worry if you’re already laughing at this; I think it is fair to say that thinking about this problem has not been the highest achievement of numismatics as a discipline. But if you’re not quite seeing the problems here, let me set them out for you.

  1. The concavity may make the coins harder to bend, but it makes them far more prone to cracking, because the edges come out so thin, as you see below. And once a coin is cracked, it’s actually in much more danger of snapping; we take a lot of care not to drop these things, in case that fault line should just complete on impact. Yet the practice was maintained for long after that would have been apparent. So, no.
  2. Electrum aspron trachy of Emperor Manuel I Komnenos, struck at Constantinople in 1143-1180, Barber Institute of Fine Arts B5702

    Electrum aspron trachy of Emperor Manuel I Komnenos, struck at Constantinople in 1143-1180, Barber Institute of Fine Arts B5702, nothing a bit of solder wouldn’t fix! (I jest.)

    Billon aspron trachy of Emperor Manuel I Komnenos, struck at Constantinople in 1143-1180, Barber Institute of Fine Arts B5758

    Billon aspron trachy of Emperor Manuel I Komnenos, struck at Constantinople in 1143-1180, Barber Institute of Fine Arts B5758, probably beyond the soldering iron…

  3. The metal quality certainly is more evident, because of those same thin edges, but in that case it would be quite important to maintain that quality. Yet the concave coins went through just the same nosedive of purity again once reformed, and you’d think that even if making them flat again would have been some kind of admission of failure, at least it would have been unclear how badly you’d failed, whereas with the concave coins there’s no hope of concealment.
  4. They just don’t stack, seriously. The manufacture was not regular enough to guarantee anything but the most basic fit. And why on earth would this have been a desirable thing here, when even cultures that use money in strung-together multiples like Chinese cash are still flat? A much better way to do this would have been to cut the designs in lower relief, or just cut them deeper than the surrounding border, so that that became the point of contact between any two coin faces. I find this one actually a silly explanation, sorry.
  5. This seems to me to presuppose a point beyond which coins were just thought too big to use, one which is only obvious if you accept that this practice shows that the Byzantine Empire had passed it. But it had used bigger coins than this before and done nothing similar. So I see no reason to accept this kind of supposed cultural universal, but even if you do, one could have achieved the same result just by making the coins thicker, which would also make them stronger. It would make them harder to strike, in terms of force, but less fragile in manufacture, easier to cut dies for and anyway, brute force was not something any pre-modern state really lacked a supply of.6
  6. In so far as I’m going to take this seriously at all, why would you start with the gold for something that would ordinarily, surely, be played with low-value coins? And why on earth would the emperor care anyway? Still more why would any subsequent emperor not repeal this in the next reform?

So, we don’t have a good explanation. In Taormina I will try to propose one that is at least less bad, and that focuses more on the manufacturing process and its changed characteristics. I have a lot to read still, and I don’t want to give away my unique selling point as yet, although I’ve tried it in the classroom a few times by now, so for now I’ll go no further, but I hope I’ve at least intrigued you with the question! And if you have answers you’d like to offer, I promise due credit if I wind up using yours alongside mine in the paper…

1. On the circumstances leading to this reform see most easily Alex Nobes, “The economic and monetary policy of the Byzantine Empire under Alexios I Komnenos” in Rosetta Vol. 11 (Birmingham 2012), pp. 56-71, online here, but you might wish to compare Michael Hendy, Studies in the Byzantine Monetary Economy c. 300-1450 (Cambridge 1985), pp. 513-517 and Alan Harvey, “Financial crisis and the rural economy” in Margaret Mullett & Dion C. Smythe (edd.), Alexios I Komnenos. Papers on the Second Belfast Byzantine International Colloquium, 14-16 April 1989, Belfast Byzantine Texts and Translations 4.1 (Belfast 1996), pp. 167-184.

2. For the actual coins, the best guide is indubitably Philip Grierson, Byzantine Coins (London 1982), pp. 211-228, esp. pp. 223-228.

3. Simon Bendall & David Sellwood, “The method of striking scyphate coins using two obverse dies, in the light of an early thirteenth century hoard” in Numismatic Chronicle 7th Series Vol. 18 (London 1978), pp. 93-104.

4. David Sellwood, “The Production of Flans for Byzantine Trachy Issues” in D. M. Metcalf & Andrew Oddy (edd.), Metallurgy in Numismatics, Royal Numismatic Society Special Publication 13 (London 1980), pp. 174-175.

5. Strength: as well as the article linked, Cécile Morrisson, “La concavité des monnaies byzantines” in Bulletin de le Société française de numismatique Vol. 30 no. 6 (Paris 1975), pp. 786-788, criticising the work of Hendy cited below, for which reason no doubt Hendy not unjustly responded in Studies in the Byzantine Monetary Economy, p. 510 n. 313, “Neither explanation [that of Grierson mentioned below or Morrisson’s] is totally satisfactory by itself, as neither takes full account of the curious inconsistency of its early usage”, and indeed I could show you flat nomismata contemporaneous with the earliest concave ones right here where I write. Indicator of metal quality: Michael F. Hendy, Coinage and Money in the Byzantine Empire 1081-1261, Dumbarton Oaks Studies XII (Washington DC 1969), p. 6; Alfred R. Bellinger & Philip Grierson (edd.), Catalogue of the Byzantine Coins in the Dumbarton Oaks Collection and in the Whittemore Collection. Volume Three: Leo III to Nicephorus III 717–1081, by Philip Grierson, Part I: Leo III to Michael III (717–867) (Washington DC 1973), pp. 5-7, to which cf. Morrisson, “Concavité des monnaies byzantines”, p. 787, accepted by Grierson, Byzantine Coins, pp. 197-198. I don’t yet have cites for the stacking or tiddly-winks theories, alas; they are much repeated but never with attribution. For the idea that the flans were now too big and had to be reined in, see Franz Füeg, Corpus of the Nomismata from Basil II to Eudocia 976-1067: corpus from Anastasius II to John I 713-976 with addenda; structure of the issues 976-1067; the concave/convex histamena; contribution to the iconographic and monetary history, ed. Italo Vecchia, transl. H. Thomas Hofmänner (Lancaster PA 2014), pp. 103-124 esp. pp. 122-124.

6. This last point, though obvious, I had to have pointed out to me by Dr Rebecca Darley.

4 responses to “A problem of concavity

  1. To prevent counterfeiting, in the same way govts today use watermarks and holograms?

    • Ah, that is indeed roughly where I’m tending. Still, it’s not simple. There have been arguments raised that the method is so hard to get right that no-one else could try, but we deduce this mainly from coins where it’s gone wrong that seem still to have been all right to let out of the mint, so, again, not perfect. But the complication and effort is perhaps a disincentive in itself…

  2. Pingback: Crusaders and money, seen in a different way | A Corner of Tenth-Century Europe

  3. Pingback: Announcing Buried Treasures | A Corner of Tenth-Century Europe

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