A while back, while wandering through a dusty old bookstore in Santa Fe, I came across an old copy of Edward Gibbon’s Decline and Fall of the Roman Empire. There was no date in it, so no indication of when it was written. I suspect around 1880, but there is no way to be sure.
In the time since I had picked up these old volumes in a book store, I had gotten my Ph.D. in paleoclimatic reconstruction and archaeology. The idea of the Roman Empire being a victim of climate change had come up here and there, but I had never seen any argument that was convincing. In my studies, I had found that those civilizations which occupied single-environmental zones — such as the Ancestral Pueblo/Anasazi of the US Southwest or Maya of the Mesoamerican jungles — tended to be the most vulnerable. The Roman Empire, at its height, stretched from Britain to Morocco to Egypt to Turkey. It, climatically, had spread its bets. A bad year in Gaul (France) might be a good year in Carthage (Tunisia).
Still, the idea that something had happened to climate has been one that Edward Gibbon himself reflected on in in his first footnote to Chapter LXIX :
1 The abbe Dubos, who, with less genius than his successor Montesquieu, has asserted and magnified the influence of climate, objects to himself the degeneracy of the Romans and Batavians. To the first of these examples he replies, 1. That the change is less real than apparent, and that the modern Romans prudently conceal in themselves the virtues of their ancestors. 2. That the air, the soil, and the climate of Rome have suffered a great and visible alteration, (Reflexions sur la Poesie et sur la Peinture, part ii. sect. 16.)
If we go to the abbe Dubos’ own words:
“ Ce qui prouve encore qu’il est survenu une altération physique dans l’air de Rome et des environs, c’est que le climat y est moins froid aujourd’hui qu’il ne l’étoit au temps des premiers Cesars, quoique le païs fut alors plus habité et mieux cultivé qu’il ne l’est à présent. Les annales de Rome nous apprennent qu’en l’année quatre cent quatre-vingt de sa fondation, l’hyver y fut si violent que les arbres moururent.”
Which very roughly translates to (my words):
“Furthermore, this proves that a physical alteration has occurred in the air of Rome and the environs; the climate is less cold there than it was at the time of the first Cesars, The country was then more inhabited and better cultivated than it is at present. The annals of Rome tell us that in the year four hundred and eighty of its foundation the winter was so violent that the trees died.”
To be fair, the Abe Dubos is not a modern mind, and neither is Gibbon. To them, climate was connected to behavior. Cold climates created hearty people who could handle adversity better than those in more gentile climates. A colder Rome would have been more virtuous than a warmer Rome.
We have the benefit of laughing at this — because we have scientific data to indicate the history of climate. But, do we even need to explain climatic influences here? The fall of Rome — the Western Empire at least — is a pretty open and shut case according to Gibbon, his predecessors, and successors: It was barbarians
In 376 A.D., tens of thousands of Therving Goths, led by Alavius and Fritigern, appeared on the banks of the Danube petitioning for entrance into the Roman Empire as refugees. They were running away from something called the Huns. Then-Eastern Emperor Valens decided to let them in, thinking he could resettle them on the border as a buffer to help guard the borders from what was coming. However, his empire was ill-able to handling such a large refugee crises, and his generals prevented access to food without paying a high price. As starvation set in, the Goths revolted, and marched south. Valens rode up and met them in 378 A.D. at Adrianople — today’s Edirne in Turkey — where the Roman suffered a catastrophic defeat. Valens himself fell in battle. The Goths dug in, and became a permanent presence between the Eastern and Western halves of the Empire. The following years saw both alliances and conflict between the two sides. Relations broke down completely after the year 400 A.D., culminating in the sack of Rome in 410 A.D. After this Roman hegemony was finished, though various institutions of the Western Roman Empire would limp along as hordes of Huns, Franks, Alemanni, Gepids, Sclavoni, Vandals, Alans, and others would roam, largely shaping the linguistic boundaries of Europe that would last to the present day.
So it was the barbarians, right? Well, that was too easy an answer for Gibbon, because for the barbarians to prosper, the Romans had to fail. Gibbon pointed to the replacement of civic virtue by a Christian after-Earth heaven and the increasing reliance on mercenaries for protection as they reason for the Empire’s decline. But even if we took that thesis as fact (and there are good reasons not to), what was in it for the Barbarians? Why did they move in such large numbers, and continue doing so long after there wasn’t a Rome to bully around?
After letting Gibbon’s books gather dust for years, I decided it was a problem worth tackling. There is a large and deep relationship between the movement of barbarians and the development of Roman civic society — one that existed centuries before the Empire’s collapse, and for centuries after as well. In fact, the development of Western civilization in Europe is inexorably tied to climate changes. But — and this is a giant, neon-flashing but — it is not a determinative relationship. This is not climate determinism, but rather climate instigation. The reactions of individuals to those changes, and the secondary and tertiary choices that emerge from those decisions, is what ultimately decided the fate of the Empire.
Last week, I published my findings in Scientific Reports
I will follow this post up with 3 other posts, because the story is quite a bit complicated. We will trace our way through first the climatic engine of Europe that has predominated during the warm, interglacial cycle we call the Holocene. This will highlight the climatic events which affected the proto-Germanic, Celtic, and Samartian tribes at the periphery of the Roman world. The next piece will take a more granular look at the history inside Rome, and how its society responded to each climatically-driven migration. Finally, we’ll take a step back and see what we can learn from this.
There are two broader points I’d like to make now to keep in mind as we go through the climate and the history. The first is that our division of the artificial and the natural is — well, artificial. Ancient societies were agrarian — around 98% of the workforce had to be farmers to support cities and armies. And farmers are very, very, very dependent on long, stable periods of climate. When climate goes south, farmers grow less food, and people start making important decisions that can impact the longevity of both themselves and their society. Much of the history of any civilization is written as if it were an exclusively political saga — this is because the primary historical writers in their ancient times saw the world in those terms. Our ability to tell the natural side of the story dates to 1924, when Arthur Douglass, working in Chaco Canyon in northwestern New Mexico, discovered that tree rings record past rainfall events. From then on, scientists have gotten better and better at writing the natural history that played alongside human history. But there’s a lot we don’t know 100% for sure— what changes in climate are important to humans? Are those reliably recorded by things like tree rings, or are other proxies better? Are the primary effects drought, or are they secondary, like say a horde of barbarians invading?
The second point is that we are biased toward human-caused explanations. The collapse of the Roman Empire is more attractive as a story about the incompetence of Honorius and the malevolence of Attila the Hun. But it is also plausible that all Emperors were more or less as incompetent as Honorius, and Attila would have happily worked as a web designer if he was afforded the opportunity. Instead, events pushed them together, and the mobile Attilas were better positioned to succeed in changing conditions. In other words, we need to step back and consider the bigger picture. This necessarily means setting the personalities aside, and looking at the climatic incentives for actions. Again — this is not a determinative factor — but it is a push that can start an avalanche.
This is also an experiment — as a scientist I spend most of my time gathering data, analyzing the data, and writing overly-technical works that get published in specialty journals. I’d like to see how a long-form read of the different components goes as far as communicating these findings. The article itself is open-access, meaning that even as a layperson you can go read it in all its technical glory. But here, I will lay out the evidence, the arguments, and the history in a (hopefully) more accessible way.
