After continuous conflict during the 570s and 580s, the Roman emperors found it increasingly difficult to pay their soldiers, a problem triggering unrest that was in turn exploited by the Iranians. In 602, they launched an open-ended offensive to seize as much Roman territory as possible, eventually annexing Syria, Palestine, and Egypt and advancing on the capital itself. In 626, a coordinated assault by Iranians and Avars on Constantinople was thwarted only by its massive fortifications and Roman sea power, and demonstrated just how vulnerable the empire had become.13
Not even the unlikely defeat of the Sasanians by last-ditch Roman campaigning and alliance-building was enough to hold off the empire’s near-terminal contraction by more than a few years. In short order, bold Arab advances into areas that had been ravaged by war for a generation led to the loss of Syria, Palestine, and Egypt (636–642). Arab raids into Anatolia commenced without delay, followed by a massive naval buildup to challenge Roman command of the seas. In 655 a large Roman fleet was defeated: the first major naval setback since an isolated disaster involving the Vandals almost 200 years earlier, it heralded the end of what the Romans had long considered “our sea.”
By then, Roman capabilities had been degraded to such an extent that Arab progress was curbed more by internal strife than by effective resistance. In the 660s, the Umayyad caliphate renewed operations with the goal of capturing Constantinople itself. The capital survived four years of seasonal naval blockades in the 670s only thanks to the deployment of a primitive version of napalm. In the meantime, the Arabs steadily advanced west of Egypt and took Roman Carthage near the end of the century. Annual raids into Anatolia were renewed in the 690s, coinciding with the rise of Bulgar power in the Balkans.
After an Arab land invasion in 717 had resulted in the loss of major cities in western Asia Minor, another failed blockade of the capital in the following year finally put an end to attempts to destroy the inner core of the empire, even if deep incursions continued into the 740s. At that point, all that was left of the Roman empire was Anatolia west of the Taurus and bits of the southern Balkans, Italy, and the surrounding islands. Sicily had only been saved by a Berber revolt against the Arabs in 740. Even after some recovery from the mid-ninth century onward, the Roman rump state—Byzantium—never again rose above the status of a midsize regional power.14
To make matters worse, Roman decline from the 540s into the eighth century coincided with the first appearance of pandemic bubonic plague in western Eurasia. In wave after wave for more than two centuries, this disease decimated populations that were expected to provide men and funds for the war effort.15
Given this near-apocalyptic onslaught from all directions, the failure of imperial restoration in Europe is not hard to explain—and certainly much easier to account for than the fact that the empire managed to survive at all, if only by a thread. Between the mid-sixth century, the high-water mark of reconquest, and the early eighth century, its territory shrank by about 60 percent, from 1.5 million to 600,000 square kilometers. Effective army strength halved from around 150,000 men in the 550s to 80,000 by the 770s. Fiscal attrition was even more severe: state revenue fell by four-fifths or more between the mid-sixth and the early eighth century. The reason that the latter exceeded the loss of territory and military strength by so much may be sought in the fact that the lost provinces had also been among the richest. A more generalized economic decline coupled with the demographic consequences of the plague also contributed: archaeological evidence points to de-urbanization and the contraction of surviving urban sites, as well as a dwindling of trade in bulk goods.16
In view of all this, there is no realistic scenario in which Roman campaigns could have continued after 540 in a way that would have resulted in durable imperial restoration. Too many obstacles arose in rapid succession. Even if the subjugation of the Ostrogoths had been handled more adroitly and the domestic problems of the Visigoths had been exploited more effectively, the Franks posed a formidable challenge, and new peripheral groups from Lombards to Slavs and Avars and later Bulgars were arrayed along an extended continental frontier, ready to probe the empire’s defenses. The Sasanian revival ended what had been an anomalously long period of peace between two powers that had traditionally been locked into expensive conflict. Renewal of this conflict in turn opened the door to opportunistic competitors, enabling the freshly united Arabs to punch well above their weight. In addition, environmental forces from plague to climate change undermined the empire’s ability to marshal the resources required to maintain its existing positions.
There is simply no moderate rewrite of history that would even remotely succeed in changing the overall trajectory of the Roman empire from near collapse to comprehensive restoration. To achieve this goal, the history of large parts of Europe and West Asia would need to be rewritten, and, moreover, so would natural history. As favorable as circumstances might have seemed when the eastern empire embarked on its ambitious westward expansion, with the benefit of hindsight we can see that this expansion occurred in the twilight of what had been an exceptionally fortuitous break from serious challenges.
It is true that some of the later setbacks were highly contingent: above all, the early Arab victories that set in motion their seemingly unstoppable advance across the Levant and North Africa might well have been averted. However, the Roman position in Europe was vulnerable to so many different competitors that longer-term outcomes could not simply be altered in favor of durable empire by modifying individual details. Between Franks, Lombards, Slavs, Avars, and Bulgars, there were simply too many moving parts and an overall redundancy in challengers to make this a defensible counterfactual strategy. At no time did the eastern empire dispose of the military manpower that had allowed late Republican and early monarchical Rome to penetrate and hold on to large parts of Western Europe. In sum, the chances of rebuilding anything resembling the mature Roman empire in Europe had been minimal.
This is important above all because the western Mediterranean campaigns represented the earliest determined attempt to restore a more hegemonic version of empire in Europe: close in time to the fall of the western Roman empire, it was therefore in some ways also the most promising. As already noted, political fragmentation had not yet progressed far. Swift victories over the Vandals—echoed by the Arabs’ later success against the Visigoths—showed that at least some of these Germanic successor regimes, sustained by fairly small coalitions of conquerors, were shallow, brittle, and consequently vulnerable to decisive strikes by a more sophisticated imperial power that commanded the seas. With few exceptions, Roman institutions of governance had not yet eroded beyond salvaging.
That the persistent congruence of adverse forces over many generations made it impossible to exploit these otherwise favorable circumstances dramatically reduced the likelihood that the Roman empire would ever be more or less fully restored. And although a more benign environment might have made it much easier to capitalize on these advantages, such a counterfactual environment is hard to create in any plausible manner: too much real-life history would have to be abandoned in the process.
The most straightforward path to imperial unity—the restoration of a preexisting edifice of rule that had fissioned only a few generations earlier—was thus solidly blocked. Any later path would need to follow a more arduous route through the creation of new governmental structures, a more demanding exercise made even more daunting once we recall the exceptional and not always replicable starting advantages Rome had initially enjoyed. The setbacks of late antiquity raised the bar for Roman-style empire in post-Roman Europe very high indeed.
THE EIGHTH CENTURY: THE ARAB CONQUESTS
With little hope of a genuinely Roman restoration of the empire on anything close to its original scale, conquest by external powers that were able to build on existing Roman institutions was the second-best option. Had the Sasanian empire and its Avar allies succeeded in taking Constantinople, long-term control over the eastern half of the former Roman empire
would have been a plausible outcome. At the same time, it is much more difficult to envision further advances into Europe. The Sasanian center of gravity was solidly set in Iran. Any attempts to penetrate Europe would have entailed considerable logistical challenges, comparable to the problems the similarly configured Achaemenid empire had encountered more than a millennium earlier.17
Operations might well have stalled in the Balkans in the face of Slav and especially Avar resistance, and campaigning in North Africa was unlikely to yield more than ephemeral gains akin to the subsequent Umayyad conquests in the Maghreb. The real-life serial defeats of the Sasanian military at the hands of Romans, Göktürks, and Arabs between 627 and 641 leave little doubt that the Sasanian forces lacked the wherewithal to establish control over the principal European territories once held by the Romans: Italy, the Iberian peninsula, and Gaul.
This leaves the Arabs as the only credible contenders. Far less tied to a developed core, they enjoyed great mobility that gave them an advantage in projecting power more widely beyond their region of origin. The explosive nature of their expansion was astounding. In 629 the great war between Rome and the Sasanians had finally ground to a halt, and the two powers had once again divided control of the eastern Mediterranean, Mesopotamia, and Iran between them. Within the next thirteen years, the Arabs seized the Roman territories in Palestine, Syria, northern Mesopotamia, and Egypt, overran Sasanian southern Mesopotamia, and crushed Sasanian resistance in western Iran.
Although their advance slowed down considerably afterward, it nonetheless continued for several generations. Eastern Iran and the Maghreb were subdued during the second half of the seventh century. As already mentioned, the caliphate also built up sufficient naval assets to challenge Roman supremacy at sea and attack Constantinople. In the 710s, Arab-led forces invaded the Iberian peninsula and destroyed the Visigothic kingdom, and took over the Indus Valley more than 6,000 kilometers to the east. In the following decades, they launched several raids into Gaul and pushed into Central Asia, where they defeated a Chinese-led army in 751—the first military encounter between East and West Asian states (figure 5.3).18
FIGURE 5.3 The Umayyad caliphate, c. 750 CE, and later successor states.
The resultant empire was very large: it covered as many as 11 million square kilometers, if arid zones are included, and up to 40 million people. Just as Rome had once controlled 80 percent of all Europeans, the Umayyad caliphate laid claim to 80 percent of the inhabitants of the Middle East and North Africa region, the same proportion as the Achaemenids had ruled in a less populous era and a considerably larger one than that controlled by the Ottomans later.19
Yet none of this had any palpable effect on European state formation: the caliphate failed to project power more deeply into Europe, and its unity ended shortly after its expansion had reached its limits. By 900, the caliphate had de facto fractured into nine major and several smaller polities that greatly differed in terms of their internal cohesion. The reasons for this outcome can be explored from two angles—by asking why the Arabs initially succeeded as they did, and why they were unable to advance further or at least maintain political integrity.
I already noted that when the eastern Roman empire embarked on its reconquest of the western Mediterranean in the 530s, unusual circumstances had made it seem more formidable than it would soon turn out to be. The same qualification applies in even greater measure to the new empire of the Arabs. Thus, the rapid pace of their initial gains owed more to exceptionally favorable geopolitical circumstances than to any intrinsic military or organizational superiority. With respect to both speed and stability, the Arab conquests were the exact opposite of Rome’s halting expansion that had been solidly undergirded by cohesive might.20
In the late sixth century, the centralization of Roman and Sasanian military power led to the disbanding of client states at these empires’ respective Arabian frontiers. This removed the previous cordon sanitaire and placed the full burden of defense on their professional armies. Once the Arabian peninsula pooled its manpower under the leadership of the Prophet and the first caliph, these empires were directly exposed to their attacks, which could hardly have occurred at a worse time. For close to three decades, the Roman and Sasanian empires had been locked into all-out war. In the Roman Levant, the Persian occupation had caused major disruptions, and although the Sasanians had formally made peace in 628, the Roman authorities had only just begun to reestablish control when the Arabs appeared on the scene a few years later. Conditions were even less settled across the border in the Sasanian domain: defeat by the Romans had triggered four years of civil war, which ended right before the Arabs first invaded.
The shocks of these preceding conflicts had created an enormous power vacuum that the Arabs eagerly exploited. Hugh Kennedy, a leading authority on their early conquests, offers a sobering counterfactual: “If Muhammad had been born a generation earlier and he and his successors had attempted to send armies against the great empires in, say, 600, it is hard to imagine that they would have made any progress at all.” And even once the two empires had fought each other to mutual depletion, Arab success remained highly contingent. Early resounding victories against Roman and Persian forces may well have been of crucial importance in making subsequent expansion possible by boosting confidence and encouraging other Arabs to join in.21
Their good fortune continued at least in part. Roman North Africa, now only tenuously connected to the imperial center, was hard to defend and, burdened by heavy taxation, perhaps not too reluctant to change masters. The forces that ventured into the Iberian peninsula went up against a usurper who had just split the Visigothic kingdom, thus unwittingly paving the ground for Arab-Berber conquest. Wherever resistance was more determined, by contrast, the Arabs faltered: Constantinople in particular tenaciously held on.
Overall, their conquests had been greatly facilitated by serious dislocations among their opponents: what had long been the principal components of two large empires had been turned into a congeries of exposed peripheries. And on top of everything else, by the time the Arab expansion commenced, the plague had ravaged the densely populated regions of the Middle East and Europe for almost a century. Resistance had been weakened by depopulation and attendant fiscal attrition. The Arabs’ avid slave-taking may well have been driven by labor shortages.22
The peculiar mode of organization of the conquering power helped it make the most of these rare opportunities. The Arab forces consisted of war-trained men, loyal to kin and tribe, and now also to their new religion. Often hardened Bedouin, they were highly mobile and able to cover large distances without slow supply trains. Their initial footprint was light, or at any rate less heavy than that of the centralizing high-maintenance empires they replaced. Their leaders demanded tribute but little else; destruction or terror remained rare.
The Arab forces settled in isolation from the local population in newly founded garrison cities, a strategy that helped them maintain cohesion and reduce friction with civilians. Thin on the ground—unlike Germans, Arabs did not resettle en masse—they did not push for religious conversion: their conquest societies were open, allowing allies to join. Islamization was slow and driven by benefits rather than compulsion. In the Christian Levant, the large Miaphysite and Nestorian communities were finally free to practice their creeds without high-handed interference from orthodox Constantinople.23
Moreover, the psychological impact of the Arab blitzkrieg must not be underrated. To them and to outsiders alike, the pace and scale of their triumphs reflected God’s will: in the 680s, the Nestorian monk John Bar Penkaye marveled that
only a short period of time passed before the entire world was handed over to the Arabs; they subdued all fortified cities, taking control from sea to sea, and from east to west—Egypt, and from Crete to Cappadocia, from Yemen to the [Caucasus], Armenians, Syrians, Persians, Byzantines and Egyptians, and all the areas in between: “their hand was upon everyone” as the prophet says.24
As the empire grew, this resulted in the emergence of effectively separate domains controlled by different forces. The two principal parties were the army of Syria (in what used to be the eastern Roman provinces) and the armies of Basra and Kufa in Iraq (in what used to be the western part of the Sasanian empire). Additional regional entities formed in due course: the army of Egypt, which later supported operations in the Maghreb and the Iberian peninsula, the army of Khorasan in Iran, and forces on the northern frontier (or Yazira). Tax revenues were largely retained within these regions and expended in the first instance on their garrisons and, at least for a while, even on the descendants of the original invaders.
This constellation precipitated interregional rivalries that were further complicated by tribal divisions within the various armies. The Umayyad caliphs, based in Damascus, relied primarily on the army of Syria. The first civil war, fought not long after the initial conquests (656–661), was in large part a struggle over supremacy and privilege between different groups in Syria and Iraq. At the same time, both armies experienced frictions between northern Arab and Yemeni elements, as well as between those whose presence preceded the conquests and later arrivals.
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