There are many theories of why Rome fell. A German historian, Alexander Demandt, counted more than 220 explanations, and a few dozen more have been proposed since he published his book in 1984.
Recently, this question again entered public consciousness, when Arron Banks, insurance multi-millionaire and a big donor to the anti-immigration UK Independence Party, opined on Twitter that “the Roman Empire was effectively destroyed by immigration.”
The classicist Mary Beard thought that this was “not just bunkum, but dangerous bunkum”, and fired back: “i think you all need to do a bit more reading in Roman history before telling us what caused the fall of Rome. Facts guys!” This lead to a “Twitter storm”, and you can read about the aftermath, from Beard’s point of view on her blog.
But it should be noted that Beard never even hinted what she thought was the cause of the decline and fall of the Roman Empire. When I twitted this observation, I was immediately challenged to point to the explanation that I favor. Fair enough. I can’t fit it in 140 characters, but I believe an 800-word blog post should suffice.
First, what is “the Fall of Roman Empire”? What are we trying to explain? Let’s rephrase this question in cliodynamic terms. In other words, we need to quantify and pay attention to dynamics (how quantities change with time).
There is no question that Roman Empire reached its peak under the “five good emperors”. There are literally dozens of quantitative measures for imperial might that all agree with each other: territorial extent, overall population, internal peace and political stability, economic activity proxied by shipwrecks and the amount of industrial pollution, monument building, production of literature and art … After the death of the last “good emperor” in 180 all these indicators headed south. Together they tell us a much more quantitative and nuanced history than an artificial binary construct of “the Fall of Rome”. As a single example, here’s the trajectory of the volume of imports of particularly fine ceramics from Africa to Italy:
If we follow these trajectories, we will learn that there were peaks and valleys. For example, a key indicator, social and political instability, went up after 180 and stayed high to the end of the third century. However, there were several peaks on top of this elevated level, recurring at roughly 50-year intervals. Such dynamical richness doesn’t fit the narrative of a “collapse.”
Most of the fourth century was relatively peaceful, but then the western half really disintegrated. The center of gravity moved east, to Byzantium, which experienced its own decline in the seventh century. Which was followed up by more cycles.
Thus, a much better question is not why Rome collapsed, but why the Roman Empire experienced those massive waves of social and political instability, accompanied by political fragmentation, population decline, and (later) dramatic loss of literacy, disappearance of monumental buildings, decrease of economic activity etc.
Let’s focus on the first of these instability waves, which followed after the last “good emperor” died. Why did it happen? Any particular event, especially one of such complexity and scale, has multiple causes. There were human errors and outright villainy. Factors peculiar to the “here and now” (such as the geography of the Italian peninsula, the arrival of the Antonine plague, climate change) also shaped the trajectory. Finally, the outbreak of massive political violence was driven by more fundamental social forces that are at play in all complex, state-level societies. Yes, the infamous “Laws of History.”
Think of astronomers studying the Solar system. A particular planet has many peculiarities – its size, color, presence or not of atmosphere, how far it is from the Sun, whether its orbit is nearly circular or more elliptic, and so on. But in addition to all that wonderful diversity, all planets also obey Newton’s Laws. So what’s the equivalent of Newton’s Laws for the dynamics of political instability in large-scale complex societies?
The short answer is the structural-demographic theory.
A somewhat longer answer, suitable for a blog: Growing political instability is first and foremost a result of elite overproduction leading to excessive intra-elite competition and conflict. This main driver is supplemented by mass mobilization of non-elites resulting from popular immiseration and by failing fiscal health of the state. A really long answer is in Chapter 7 of Secular Cycles (for the crisis of the third century in Rome) and in an article by David Baker (for what happened after that).
Once again, all kinds of additional factors played a role, but if you are interested in general principles, understanding why empires decline and fall, then the structural-demographic theory is your best friend.
Here’s the reference to Demandt’s book if anybody cares to read about the 220 theories (and reads German):
Demandt, Alexander. 1984. Der Fall Roms: die Auflösung des römischen Reiches im Urteil der Nachwelt. Munich: Beck.