I want to start with the observation I offer whenever I am asked (and being a Romanist, this happens frequently) “why did Rome fall?” which is to note that in asking that question we are essentially asking the wrong question or at least a less interesting one. This will, I promise, come back to our core question about diversity and the fall of Rome but first we need to frame this issue correctly, because Rome fell for the same reason all empires fall: gravity.

An analogy, if you will. Imagine I were to build a bridge over a stream and for twenty years the bridge stays up and then one day, quite unexpectedly, the bridge collapses. We can ask why the bridge fell down, but the fundamental force of gravity which caused its collapse was always working on the bridge. As we all know from our physics classes, the force of gravity was always active on the bridge and so some other set of forces, channeled through structural elements was needed to be continually resisting that downward pressure. What we really want to know is “what force which was keeping the bridge up in such an unnaturally elevated position stopped?” Perhaps some key support rotted away? Perhaps rain and weather shifted the ground so that what once was a stable position twenty years ago was no longer stable? Or perhaps the steady work of gravity itself slowly strained the materials, imperceptibly at first, until material fatigue finally collapse the bridge. Whatever the cause, we need to begin by conceding that, as normal as they may seem to us, bridges are not generally some natural construction, but rather a deeply unnatural one, which must be held up and maintained through continual effort; such a thing may fail even if no one actively destroys it, merely by lack of maintenance or changing conditions.

Large, prosperous and successful states are always and everywhere like that bridge: they are unnatural social organizations, elevated above the misery and fragmentation that is the natural state of humankind only by great effort; gravity ever tugs them downward. Of course when states collapse there are often many external factors that play a role, like external threats, climate shifts or economic changes, though in many cases these are pressures that the state in question has long endured. Consequently, the more useful question is not why they fall, but why they stay up at all.

And that question is even more pointed for the Roman Empire than most. While not the largest empire of antiquity, the Roman empire was very large (Walter Scheidel figures that, as a percentage of the world’s population at the time, the Roman Empire was the fifth largest ever, rare company indeed); while not the longest lasting empire of antiquity, it did last an uncommonly long time at that size. It was also geographically positioned in a space that doesn’t seem particularly well-suited for building empires in. While the Mediterranean’s vast maritime-highway made the Roman Empire possible, the geography of the Mediterranean has historically encouraged quite a lot of fragmentation, particularly (but not exclusively) in Europe. Despite repeated attempts, no subsequent empire has managed to recreate Rome’s frontiers (the Ottomans got the closest, effectively occupying the Roman empire’s eastern half – with a bit more besides – but missing most of the west).

The Roman Empire was also, for its time, uncommonly prosperous. As we’ll see, there is at this quite a lot of evidence to suggest that the territory of the Roman Empire enjoyed a meaningfully higher standard of living and a more prosperous economy during the period of Roman control than it did either in the centuries directly before or directly after (though we should not overstate this to the point of assuming that Rome was more prosperous than any point during the Middle Ages). And while the process of creating the Roman empire was extremely violent and traumatic (again, a recommendation for G. Baker, Spare No One: Mass Violence in Roman Warfare (2021) for a sense of just how violent), subsequent to that, the evidence strongly suggests that life in the interior Roman Empire was remarkably peaceful during that period, with conflicts pushed out of the interior to the frontiers (though I would argue this almost certainly reflects an overall decrease in the total amount of military conflict, not merely a displacement of it).

The Roman Empire was thus a deeply unnatural, deeply unusual creature, a hot-house flower blooming untended on a rocky hillside. The question is not why the Roman empire eventually failed – all states do, if one takes a long enough time-horizon – but why it lasted so long in such a difficult position. Of course this isn’t the place to recount all of the reasons why the Roman Empire held together for so long, but we can focus on a few which are immediately relevant to our question about diversity in the empire.

Bret Devereaux, “Collections: The Queen’s Latin or Who Were the Romans, Part V: Saving and Losing and Empire”, A Collection of Unmitigated Pedantry, 2021-07-30.