A Roman "Aureus" minted by Emperor Septimius Severus in 193 CE. At nearly 8 grams, the Aureus was truly an imperial coin - the embodiment of Rome's wealth and power. (image from Wikipedia).
In this post, I argue that precious metal currency was a fundamental factor that kept together the Roman empire and gave to the Romans their military power. But the Roman mines producing gold and silver peaked in the first century CE and the Romans gradually lost the capability of controlling their resources. In a way, they were doomed by "peak gold."
When I heard for the first time that the Roman Empire fell because of the depletion of its silver and gold mines, I was skeptical. Compared to our situation, where we are facing the depletion of fossil fuels, the Roman case seemed to me to be completely different. Gold and silver don't produce energy, they don't produce anything useful. So, why should the Roman Empire have fallen because of something we might call "peak gold"?
And yet, as I delved into the matter, I noticed how evident was the correlation of declining gold and silver availability with the decline of the Roman Empire. We have scant data on the production of Roman mines, mainly located in Spain, but it is commonly believed that production peaked at some moment during the first century CE (or perhaps early 2nd century CE). Afterwards, it rapidly dwindled to nearly nothing, even though gold mining never completely stopped (1).
As you can see in the figure, the loss of precious metal production was reflected in the silver content of the Roman currency. The Romans didn't have the technology needed to print paper bills, so they just debased their silver currency, the "denarius," by increasing its copper content. By mid 3rd century, the denarius was nearly pure copper: "fiat money" if there ever was one. During that period, gold coins were not debased, but they basically disappeared from circulation. (graph above from Joseph Tainter (2)).
As I argued in a previous post, the progressively dearth of precious metals correlates well with the various events that took place during the declining phase of the empire and with its eventual disappearance. Of course, correlation doesn't mean causation but, here, the correlation is so strong that you can't think it is just a question of chance. With time, it appeared clear to me that there were also clear links between several factors in the collapse of the Empire.
In general, complex systems tend to fall in a complex manner and the Roman Empire did not simply fall because of the lack of its primary energy source which, at that time, was agriculture. Energy (and power) is useless without control and for the Romans controlling the energy generated by agriculture requires capital investments for troops and bureaucracy. Both were affected by the decline of the production of precious metals. In time, the reduced military effectiveness of the empire disrupted the ability of controlling the agricultural system. That condemned the Empire to collapse.
This is a hugely complex story that can't possibly be exhausted with a mere blog post. Nevertheless, the problem is very general and it can be condensed in a single sentence: "power is nothing without control" So, I believe it is possible to lay down in a relatively short space the main elements of the interplay between gold, military power, and food in Roman times. Let me try.
- The Romans and gold
Ultimately, what creates and keeps together empires is military force. The Roman Empire was so large and so successful because it was, possibly, the mightiest military force of ancient times. The Romans had been so successful at that not because of special military innovations. The recipe for their success was simple: they paid their fighters with precious metal currency. The combined technology of gold mining and coin minting had allowed the Romans to create one of the first standing armies in history. Still today, we call our enlisted men "soldiers", a term that comes from the Roman word "Solidus;" the name of the late empire gold coin.
Not only money could create a standing army, it could also swell it to large sizes. Enlisting in the legions - the backbone of the army - was reserved to Roman citizens, but anyone could enlist in the "auxilia", "auxiliary" troops. In the figure, you see Roman auxilia (recognizable by their round shields) presenting the severed heads of Dacians to Emperor Trajan during the Dacian campaign of the 2nd century CE. Normally, Romans were not supposed to cut off enemies' heads, it was seen as uncivilized, but the auxilia were notoriously a little unruly (note how the Emperor, on the left, looks perplexed). But, by the time of the Dacian wars, theauxilia had become a fundamental part of the Roman army and they were to remain so for the remaining lifetime of the Empire.
Gold and silver were essential elements in the hiring of troops for the Romans and that was especially true for foreign ones. Put yourself in the caligae (sandals) of a German fighter. Why should you put your framea (lance) in the service of Rome if not because you were paid? And you wanted to be paid in serious money; copper coins would not do. You wanted gold and silver currency that you knew could be redeemed anywhere in Europe and especially in that gigantic emporium of all sorts of luxury goods that was the city of Rome, the largest of the ancient world. And, by the way, where did these luxury items come from? Mostly, were imported. Silk, ivory, pearls, spices, incense, and much more came from India and China. Importing these items was not just an extravagant hobby for the Roman elite, it was a tangible manifestation of the power and of the wealth of the empire; something that was an important factor in convincing people to enlist in the auxilia. But the Chinese wouldn't send silk to Rome in exchange for worthless copper coins - they wanted gold and they obtained it. Then, that gold was lost forever for the Empire which, basically, could produce only two things: grain and troops, neither of which could be exported at long distances.
This situation explains the gradual military decline of the Roman empire. With the decline of the precious metal mines, it became more and more difficult for emperors to recruit troops. The lack of a strong central power caused the empire to become engulfed in civil wars; with the army mainly engaged in fighting chunks of itself and the empire splitting in two parts: the Eastern and the Western. During this phase, the number of troops was not reduced, but their quality strongly declined. After the military reform by Emperor Diocletian during the third century CE, the Roman army was formed mainly of limitanei; not really an army but a border police unable to stop any serious attempt on the part of foreigners to puncture the borders. To keep the empire together, Emperors relied on the "comitatenses" (also with other names) mobile crack troops which would plug (or try to plug) the holes in the border as soon as they formed.
The combination of limitanei and comitatenses worked in keeping the barbarian out of the Empire for a while. But the hemorrhage of gold and silver continued. So, during the last decades the empire, the paradigmatic Roman troops were the "bucellarii" a term that means "biscuit eaters". The name can be taken as implying that these troops fought for food. Of course that may not have been always true, but it is a clear indication of the dearth of money of the time. There are also reports of troops paid in pottery and in some cases with land - the latter use may have been a factor in creating the feudal system that replaced the Roman empire in Europe.
In a way, as we see, the Romans were doomed by their "peak gold" (and also "peak silver). By the loss of their precious metal supply, the Romans lost their ability of controlling their troops and as a result of their resources. And power is nothing without control.
But the Roman empire did not fall just because it was invaded by foreigners or because it split in multiple sectors. It experienced a systemic collapse that wasn't just a military one: it involved the whole economy and the social and political systems as well. To understand the reasons of the collapse, we need to go more in depth in the way the Roman economic system worked.
- The Romans and energy
The energy of the Roman Empire came from agriculture; mainly in the form of grain. At the beginning of their history and for several centuries onward, it seems that the Romans had little or no problems in producing enough food for their population. That makes sense considering that in Roman times the population of Europe was less than one tenth of what it is today and hence there was plenty of free space for cultivations. Reports of food problems in the Empire appear only with the 1st century CE and truly disastrous famines appear only with the 5th century CE - when the Western Roman Empire was already in its terminal phase. "Peak food", apparently, came much later, about 3-4 centuries later than "peak gold".
The very existence of a "peak food" for the Roman empire is somewhat puzzling: agriculture is, in principle, a renewable technology that had been able to feed the Roman population for several centuries. During the last period of the empire, there is no evidence of a population increase; on the contrary, it is clear that it declined. So, why couldn't agriculture produce enough food?
The problem is that producing food doesn't just involve plowing some land and sowing crops. Agricultural yields depend on the vagaries of the weather and, more importantly, agriculture has the tendency of depleting the land of fertile soil as a result of erosion. To avoid this problem, the ancient had a number of strategies: one was nomadism. From Caesar's "De Bello Gallico" we learn that, as late as in the 1st century BCE, European populations still practiced a nomadic life style. They would do that in order to find new, pristine land and planting crops in the rich soil that they could produce by slashing and burning trees. That was possible because continental Europe, at that time, was nearly empty of people and entire populations could move unimpeded.
The Romans, instead, were a sedentary population and they had the problem of soil depletion. As population grew, it became a larger and larger problem, especially in a mountainous region such as Italy (3). In addition, some urban centers - such as Rome - became so big that they were impossible to supply using just local resources. With the 1st century BCE, the situation led to the development of a sophisticated logistic system based on ships that carried grain to Rome from the African provinces, mainly Libya and Egypt. It was a major task for the technology of the time to ensure that the inhabitants of Rome would receive enough grain and just when they needed it. It required large ships, storage facilities and, more than all, a centralized bureaucracy that went under the name of "annona" (from the Latin world "annum", year). So important it was this system, that Annona was turned into a full fledged Goddess by imperial propaganda (you can see her in the image above, on the back of a coin minted at the time of Emperor Nero - from Wikipedia). For us, turning bureaucracy into a divine entity may appear a bit farfetched but, perhaps, we are not so far away from that.
Despite its complexity, the Roman logistic grain system was successful in replacing the insufficient Italian production and it permitted to feed a city as large as Rome, whose population approached (and perhaps exceeded) one million inhabitants during the heydays of the empire. But it was not Rome alone which benefited from the annona and the system could create a relatively high population density concentrated along the shores of the Mediterranean sea. It was this higher population density that gave to the Romans a military edge over their Northern neighbors, the "barbarians", whose population was limited by a lack of a similar logistic system.
But what actually moved grain from the shores of Africa to Rome? In part, it was the result of trade. For instance, grain shipping companies were in private hands and they were paid for their work. But grain itself didn't move because of trade: the provinces shipped grain to Rome because they were forced to. They had to pay taxes to the central government and they could do so either in currency or in kind. It seems that grain producers paid usually in kind and Rome didn't ship anything in return (except in terms of troops and bureaucrats). So, the whole operation was a bad deal for provinces but, as usual in empires, opting out was not allowed. When, in 66 CE, the Jews of Palestine decided that they didn't want to pay taxes to Rome any more, their rebellion was crushed in blood and Jerusalem was sacked. In the end, it was military power that kept the system under control.
But the system that fed the city of Rome appears to have rapidly declined and finally collapsed during the 5th century CE. We have some evidence (3) that it was in this period that erosion turned the North African shores from the Roman "grain belt" into the desert we see nowadays. Possibly, the disaster was unavoidable, but it is also true that warfare does a lot of damage to agriculture and this is surely true for the North African region, object of extensive warfare during the last period of the Roman Empire. More in general, the strain to the economic system generated by continuous warfare may have led producers to overexploit their resources, privileging short term gains to long term stability. Were it not for these events, it is likely that the agricultural productivity of the land could have been maintained for a much longer time. But that was not the case.
With the North African land rapidly turning into a desert, King Genseric of the Vandals (see his face on a "siliqua" coin in the figure), ruling the region, halted the shipping of grain to Rome in 455 CE, then proceeding to sack the city in the same year. That was the true end of Rome, whose population shrunk from at least a few hundred thousands to about 50,000. It was the end of an age and never again would the North African shores be exporters of food.
- The fall of the Roman empire
Complex systems tend to fall in a complex manner and several interlocked factors played a role together first in creating the Roman empire, then in destroying it. At the beginning, it was a technological innovation, coinage of precious metals, that led the Romans to develop a military might that allowed them to access a resource which would have been impossible to exploit otherwise: the North African agricultural land. But, as it is often the case, the exploitation mechanism was so efficient that eventually it destroyed itself. Lower productivity of the precious metal mines reduced the efficiency of the Roman military system and this, in turn, led to fragmentation and extensive warfare. The increasing needs of resources for war were an important factor in destroying the agricultural system whose collapse, in turn, put an end to the empire.
The dynamic interplay of the various elements involved in the growth and the fall of the empire can be seen in the figure below, from a previous essay of mine. In the diagram, the source of energy is agriculture, but it is just an element of a complex system where various entities reinforce or dampen each other.
The diagram is patterned after the one originally created by Magne Myrtveit for our society described in the 1972 "Limits to Growth" study. This, as other studies of the same kind, provide a nice, aggregated view of the trajectory of an economic system which tends to overexploit the resources it used. As models, however, they are not completely satisfactory in the sense that they don't include the question of control. It is a cost which needs to be paid and the gradually declining flow of resources makes it difficult. As a result, empires rarely collapse smoothly and as a whole, but rather tend to fragment and engage in internecine wars before actually disappearing. That was the destiny of the Roman Empire which experienced the general rule that power is nothing without control.
The Romans and us
It has always been fashionable to see the Roman Empire as a distant mirror of our civilization. And, indeed, we see that the points of contact are many. Just think of the sophisticated Roman logistic system: the navis oneraria which transported grain from Africa to Rome are the equivalent of our super-tankers transporting crude oil from the Middle East to Western countries. And think how China and India are playing today exactly the same role they were playing in the remote Roman times: they are manufacturing centers which are gradually soaking the wealth of the empire that we call, today, "globalization".
This said, there is also an obvious difference. The Roman energy system was based on agriculture and hence it was theoretically renewable, at least until the Romans didn't overexploit it. Our system is based on fossil fuels, which are obviously non renewable resources. Hence, we tend to be more worried about the depletion of our energy resources rather than that of gold and silver which - it seems - we could safely remove from our financial system without evident problems.
Still, there remains the fundamental problem that power is useless without control. The control system of the globalization empire works on similar principles as the older Roman one. It is based on a sophisticated financial system which, eventually, works because it is integrated with the military system. In the globalized army, soldiers, just like the Roman ones, want to be paid. And they want to be paid with a currency that they can redeem with goods and services somewhere. The dollar has, so far, played this role, but can it play it forever?
Eventually, everything that humans do is based on on some form of belief of what has value in this world. The Romans saw gold and silver as stores of value. For us, there is a belief that bits generated inside computers are stores of value - but we may be sorely disappointed - not that there will ever be a "peak bits" as long as there are computers around, but surely a major financial collapse would not just impoverish us, but most of all it would disrupt our capability of controlling the energy resources we need so desperately.
So, when oil pundits line up oil reserves as if each barrel were a soldier ready for battle, they tacitly assume that these reserves will available for use of the global empire. That's not necessarily true. It depends on the degree of control that the empire will be able to exert on producers. That depends on the financial system which may well turn out to be the weak link of the chain. Without control, power is useless.
The Roman empire was lost when the financial system ceased to be able to control the military system. When the Romans lost their gold, everything was lost. In our case, it may well be that we will lose our ability to control the military system before we actually lose our ability to produce energy from fossil fuels. If the dollar loses its predominance in the world's financial system, then producers may be tempted to keep their oil for themselves or, at least, not so enthusiastic any more in allowing the Empire to access it. What's happening today in Ukraine may be a first symptom of the impending loss of global control.
1. "Mining in the Later Roman Empire", J.C Edmondson, The Journal of Roman Studies, 79, 1989, 84,http://www.jstor.org/stable/301182
2. Tainter, Joseph A (2003. First published 1988), The Collapse of Complex Societies, New York & Cambridge, UK:Cambridge University Press, ISBN 0-521-38673-X,
3. "The Roman Empire: Fall of the West; Survival of the East", James F Morgan, Bloomington 2012