Historians are still arguing about why and how (and even when) the Roman Empire fell — and by extension why, how and when the “Middle Ages” and “Europe” (ie, northwestern Europe as we understand it) began.

One theory is that the answer is to be found, somewhat surprisingly, not in northwestern Europe but on the opposite side of the former Roman Empire. This story-line involves Muhammad, Islam and the Arab conquests in the century after Muhammad’s death in 632. The stages of those conquests you see in the map above.

In this post, I want to introduce that thesis to you and the one it tried to replace.

I do this not in order to endorse either thesis, but in order to celebrate the elegant and imaginative beauty of the thought processes of the two historians who produced them.

These two thinkers are

• Edward Gibbon and
• Henri Pirenne,

and I am hereby including them into my pantheon of the world’s greatest thinkers.

(Which reminds me: Scientists and philosophers are currently over-represented on my list, so I am also retroactively including the historians Herodotus, Polybius, Livy and Plutarch. Thucydides is already on the list.)

And at the end of the post, I’ll ponder what this eternal debate about Rome tells us about intellectual theorizing in general.

My source, besides the books of Gibbon and Pirenne, is Philip Daileader’s excellent lecture series on the Early Middle Ages.

I) Edward Gibbon

Gibbon was a typical specimen of the Enlightenment. He hung out with Voltaire, considered religion (and especially Christianity) a load of superstitious poppycock, trusted in human reason and was enamored by the classics.

Being a man of independent means, he was able to devote all his time and energies to investigating what he considered the great mystery of antiquity. Why did the Roman Empire fall?

The result was an epic work of beautifully written English prose called The Decline and Fall of the Roman Empire. The first of its six volumes came out in the year of America’s Declaration of Independence.

The book was so powerful that its thesis turned into what we would call a meme. Ask any semi-literate person today why the Roman Empire fell and he is likely to answer something like this:

Barbarians invaded → Rome fell

Gibbon’s thesis in more detail

In brief, Gibbon believed that the Roman Empire was

1. in part a victim of its own success, having prospered so much that its citizens had become soft, and
2. in part a victim of Christianization, which replaced the pagan warrior ethic with an unbecoming concern for the hereafter.

As Gibbon famously said, Rome’s

last remains of military spirit were buried in the cloister.

This corrosion of morals or values, according to Gibbon, left the Western Roman Empire (Diocletian had divided it into two halves, east and west, for administrative purposes) vulnerable to the blonde hordes from the north.

And thus, federations of Germanic tribes crossed the Rhine and Danube and ransacked the Roman Empire, eventually sacking Rome itself and deposing the last (Western) Roman emperor in 476.

The Ostrogoths and Lombards took Italy, the Visigoths took Spain and the Franks took Gaul (→ Francia, France).

Within a few generations, one Frankish family, the Carolingians, seized power. Under Charlemagne (= Carolus Magnus, Karl der Grosse, Charles the Great), the Carolingians then united much of western Europe, an area that happens to overlap almost perfectly with the founding members of the European Union.

In the nice round year of 800, Charlemagne, the king of Francia, became a new Emperor. He sparked a small cultural and economic recovery (the “Carolingian Renaissance”), but his descendants bickered about inheritance, and the Carolingian empire split into what would become France, the Low Countries and Germany.

And there we have it: “Europe”.

II) Henri Pirenne

Like Gibbon, Henri Pirenne was a man of his time. But that time was the late nineteenth and early twentieth century. Historians now felt that “moral” explanations of history were a bit woolly and preferred to think in terms of impersonal, and primarily economic, forces rather than great individuals or events.

And this led Pirenne, a Belgian (and thus a Carolingian heir), to a very different, and extremely original, thesis. The title of his monumental book, Mohammed and Charlemagne, essentially says it all.

The Pirenne thesis begins with a view that, first of all, nothing noteworthy “fell” in 476. Who cares if an emperor named, ironically and aptly, “little Augustus” (Romulus Augustulus) was deposed in that year? Roman civilization went on exactly as before. To most Europeans, nothing whatsoever changed.

That civilization was

1. urban
2. Mediterranean and
3. Latin in the West

The Germanic tribes in fact came not to destroy but to join this civilization. They had entered the Roman Empire long before 476 to live there in peace, but were forced repeatedly to move and fight. When they eventually deposed the Romans, the Barbarians settled in the Roman cities and gradually adopted Latin (which was by this time, and partially as a result, branching into dialects that would become Catalan, Spanish, French etc).

Most importantly, the Mediterranean (medius = middle, terra = land) remained the center of this world, and trade across its waters enriched and fed all shores, north and south, east and west.

So what changed?

What changed was that Muhammad founded Islam, united the Arabs and then died. Suddenly, the Arabs poured out of the desert and conquered everything they encountered.

Look again at the map at the very top. In effect, the Arabs conquered the entire southern arc of the former Roman Empire until Charles Martel (Charlemagne’s grandfather) stopped them near Poitiers in France.

The Arabs thus split the Mediterranean in two. Suddenly, the “Mediterranean” was no longer the center of the world, but a dividing line between two worlds.

Ingeniously, Pirenne then inferred the rest of his thesis from archaeological finds: In the years after the Arab conquests, papyrus (from Egypt) disappeared from northwestern Europe, forcing the northerners to write on animal hides. Locally minted coins disappeared, too. Gone, in fact, was everything that was traded as opposed to produced locally.

The Arabs, Pirenne concluded, had blockaded and cut off northern Europe from the rest of the world. Europe thus became a poor, benighted and involuntarily autarkic  backwater.

This, finally, amounts to the “fall” of Roman civilization in northwestern Europe. Roman cities, administration and customs disintegrated. Europe becomes a small and isolated corner of the world.

It is within this then-forgettable corner that the Carolingians rise and create “Europe”. As Pirenne famously said:

Without Islam, the Frankish Empire would have probably never existed, and Charlemagne, without Muhammad, would be inconceivable.

III) So who was right?

I promised to ponder what this debate might say about intellectual theorizing in general. Well, here goes:

1) Nobody needs to be wrong

As it happens, neither Gibbon nor Pirenne have ever fallen out of favor. Both are still considered to have got much of their interpretation right. The caveat is merely that their theses are considered … incomplete.

We encountered such a situation when talking about Newton and Einstein. Einstein in effect proved Newton “wrong”, and yet we have never discarded Newton, just as we won’t discard Einstein when somebody shows his thinking to have been incomplete.

2) Progress = making something less incomplete

Although both Gibbon’s and Pirenne’s theses were incomplete, they add up to an understanding that is less incomplete, so that others can make it even less incomplete.

This, in fact, is what has been happening. Subsequent historians have wondered why, if their theories were true in the West, the Eastern Roman (ie, Byzantine) Empire did not fall for another millennium.

Regarding Gibbon: The East, too, faced Barbarian invasions (from the same tribes). And the East was even more Christian than the West. So something must be missing in Gibbon’s explanation.

Regarding Pirenne: The East, too, was cut off from the south by the Arab conquests (though perhaps not as much).

IV) One possible omission: depopulation

So, even though both Gibbon and Pirenne, may well have been right, that there had to be at least one more factor: disease.

Perhaps it was smallpox arriving from China, and later plague. Perhaps it was something else. (The theory of massive lead poisoning is now discredited. Again: They had lead pipes in the East and the West.)

Whatever the disease(s), the population of the Roman Empire collapsed. And the West, which had fewer people than the East to begin with, became largely empty.

Its cities were deserted. Rome’s population was 1 million during the reign of Augustus but 20,000 by the time of Charlemagne. People used the Roman baths of northern cities as caves. New city walls were built with smaller circumferences than older city walls.

Fields and land lay fallow, too. We know this because taxes were levied on land (not labor), and tax revenues fell due to agri deserti, “abandoned fields”.

Viewed this way, both the Germanic invasions that Gibbon focussed on and the Arab invasions that Pirenne focussed on were perhaps not a cause but a symptom of the fall of Rome. It seems likely that the Germans and Arabs showed up because there were few people blocking their way, and conquered for that same reason.

If we ever find out the complete answer, it will be because Gibbon and Pirenne pointed us in the right direction.