A press release is going around about a dietary analysis of Roman gladiator skeletons from Imperial-era Ephesos, headlined "Roman gladiators ate a mostly vegetarian diet and drank a tonic of ashes after training."
While I haven't had time to carefully and thoroughly dissect the publication, which came out last week in PLoS (Losch et al. 2014), it seems reasonably sound. The published C/N isotope ratios are totally in line with what we'd expect from the Roman diet--and also show the variation that we expect to see around the Empire. (I have to confess I'm a bit miffed that they discuss all the C/N isotope studies from around Rome but not Killgrove & Tykot 2013 from Rome itself.)
The Sr/Ca trace element analysis is potentially more problematic. Again, a confession: I don't fully understand the mechanics of the process of trace element analysis, nor the major issues with diagenesis (the chemical deterioration of organic skeletal components, like collagen, that can affect measurement of things like trace elements). I do know that the ability to control for diagenesis has made great advances in recent years, meaning studies like trace Pb analysis are now possible. But if I trust the researchers that they controlled for diagenesis to the best of their abilities, their Sr/Ca results are very interesting.
|Relief of two gladiatrices from Halicarnassus|
All in all, this seems to be a very well-designed study that answers interesting research questions but leaves others open for more research (from other cemeteries or with other methodologies).
My only complaint (you knew a complaint was coming, right?) is that the "only female to be found in the gladiator cemetery" seems to be treated as an anomalous burial rather than, dare I say it?, a gladiator -- or gladiatrix -- herself. (I'm not sure what that conclusion was based on; perhaps some archaeological context?) But, her slightly different diet (higher in millet or millet-consuming animals than the men's diets, and whatever her Sr/Ca ratio was) would be really interesting interpreted against a backdrop of gender differences in gladiatorial games.
Update (10/23/14) - I was asked to comment on this study for a news article in the Biblical Archaeology Review blog, and that led me to this 2008 article in Archaeology Magazine (vol. 61, issue 6) - The Gladiator Diet. It seems to be based on both a 2007 AAPA abstract (PDF here, p. 139) and some then-new isotope results. I couldn't find anything in between the 2008 news piece and the 2014 publication. The time-delay to publication is curious but not abnormal, especially if the authors had to run additional tests for diagenesis.
Update (10/25/14) - I read the article a bit more thoroughly in advance of a comment I gave to NPR's Maria Godoy for her article "Gladiator Gatorade?". Some further thoughts:
- First, although the average gladiator diet shows consumption of C3 resources (wheat and barley) and a N value somewhere between beans and terrestrial meat, there is plenty of variation. There were gladiators who ate a more veggie diet, and those who ate a more meat-heavy diet. This variation, though, is precisely what we see in other Roman Imperial dietary isotope studies. The headline that gladiators were vegetarian is not at all right.
- Second, the Sr/Ca ratios are indeed much higher for the gladiators than for the contemporaneous people. This is strong evidence for the gladiators' consuming a lot of calcium from a source that doesn't show up in the isotopes -- while ash-drink (likely made from poplar wood, which has a particularly high Sr/Ca ratio and is abundant at Ephesos) is a definite possibility, the authors admit they can't exclude something slightly more mundane, like dairy.
- Third, the discussion of the "only female from the gladiator cemetery" is confusing. Based on the sample number, she was from a nearby cemetery context that included other females. Her C ratio suggests she ate more millet (or animals foddered on millet) than the other locals, and her S ratio also makes a strong case for her being nonlocal. Her Sr/Ca ratio is not as high as the male gladiators'. If she is from the gladiator cemetery, this is really very interesting -- she's from somewhere else, recently arrived, and not taking a Ca supplement. I'm still not sure why the authors exclude her from being a gladiatrix, nor why they call her the only female in that cemetery. I suspect I'd have to delve into the archaeological context to find out more.
- Finally, the authors' full discussion of diagenesis is quite good, and I am convinced that there is a significantly higher Sr/Ca ratio in the gladiators. However, I am not convinced by the bone turnover discussion -- they try to control for physical activity, but they don't take into account things like pathology -- nor their conclusions from it about when the gladiators died. Still, it's an interesting direction in which to push the data, and I hope that eventually we will be able to confirm this kind of hypothesis when we know more about bone turnover and diagenesis.
Burton JH, & Wright LE (1995). Nonlinearity in the relationship between bone Sr/Ca and diet: paleodietary implications. American Journal of Physical Anthropology, 96 (3), 273-82 PMID: 7785725.
Killgrove, K., & Tykot, R. (2013). Food for Rome: A stable isotope investigation of diet in the Imperial period (1st–3rd centuries AD) Journal of Anthropological Archaeology, 32 (1), 28-38 DOI: 10.1016/j.jaa.2012.08.002.
Lösch S, Moghaddam N, Grossschmidt K, Risser DU, & Kanz F (2014). Stable Isotope and Trace Element Studies on Gladiators and Contemporary Romans from Ephesus (Turkey, 2nd and 3rd Ct. AD) - Implications for Differences in Diet. PloS one, 9 (10) PMID: 25333366.