Commentary on the National Geographic Article: "Roman Walls" (NatGeo Sept. 2012)

The following is my analysis and critique an article appearing in the September 2012 edition of National Geographic magazine.  This represents part of a much larger project on how societies respond to deep political-economic, socio-cultural, and environmental change.  The Roman Empire--in its various manifestations--provides a rich source of case studies on how a society expands, collapses, encounters change, and subsequently adapts to new realities.  And in so doing, it also helps to alter those same realities. I am asserting here that, embedded deep in this history are some important lessons for modern, fossil-fuel-based civilization, as well.  -- Blaine

Source: http://ngm.nationalgeographic.com/2012/09/roman-walls/curry-text

Andrew Curry has written a very thought-provoking article in the September 2012 edition of National Geographic magazine.  The topic: the massive Roman imperial project known as Hadrian’s Wall.  He starts off by noting the concerted international effort (spearheaded by the United Nations) to preserve the wall; and from there he quickly moves to pose the question that drives the rest of his article:

The international effort may help answer a surprisingly tricky question: Why did the Romans build the walls? To protect a regime besieged by barbarians, or simply to establish the physical edge of the empire?

As I read this article, I couldn’t help but have the feeling that the author’s question was as much about us modern folk today, as it was about military policy-makers in ancient Rome.  The issue of walls has become highly relevant (for Americans as well as others) again, as issues of massive demographic shifts become resurgent: keeping “them” out; protecting “our homeland”; halting “terror”; drawing “lines in the sand,” etc.  Each of these metaphors can conjure up images of a society’s desire to build “a wall” of both self-definition and self-imposed security, as a bulwark against encroaching “foreign” elements. 

At the risk of clarifying the obvious, walls have the capacity to keep people in as well as keep people out.   Likewise, they can say just as much about the people defined as “inside” as they do about those on the “outside.”  Indeed, concepts of “inside” and “outside” exist in symbiosis.  You can’t have a concept of one without some concept of the other. 

This, in turn, gets to fundamental issues of human perception.  Indeed, just as we can perceive things in physical space, we can likewise conceive of things in conceptual or theoretical space.  In constructing a physical wall, Emperor Hadrian was also making an explicit—or “concrete”—statement about the concept of Empire itself.  Indeed, he helped to both limit the Empire’s expansion, and, in the process he also helped Romans to more finely delimit (or frame) the very concept of their own Empire.  Implicitly, perhaps unconsciously, Hadrian was also putting a wall around the imperative toward the classic problem of “imperial overreach.”  Furthermore, as any good student of public administration or public policy knows all too well, solid solutions to one set of complex, large-scale social problems tend to—with a certain amount of lag time—bring on a whole new set of problems.  Such is the Sisyphean nature of the human condition, writ large.      

Walls Define Limits—Both Physical and Conceptual

Barbarians (non-Romans) were often used to construct large-scale projects on the periphery of the Roman Empire.  This scene depicts one such project in the British Isles.


In the case of the adept leader, Hadrian, he had to contend with a well-established Roman Army, deeply entrenched in its own traditions, and its self-perception of how war and conquest should be pursued. 

The new emperor’s policies ran up against an army accustomed to attacking and fighting on open ground. Worse, they cut at the core of Rome’s self-image. How could an empire destined to rule the world accept that some territory was out of reach?

In short, the Romans were starting to enter a more mature phase in their collective thinking and outlook.  They were confronting the same sets of factors that all growth-oriented imperial structures and/or economic systems must inevitably face: the very real prospect of diminishing marginal returns to growth or expansion.  This is the Peter Principle, writ large: things simply grow and expand until they are stretched beyond their normal carrying capacity.  

This is one of the classic definitions of the term “overshoot.”  Growth-oriented systems overshoot their ability to function normally.  Systemic instability is the natural result of overshoot.  And with such instability is the concomitant threat of collapse, if not outright destruction.[1]  My relatives from North Carolina had an elegantly simply phrase for this concept: if referring to a person, they would simply state that “so-and-so had gotten too big for his britches.”  Scholars and intellectuals often prefer other terms or phrases, however.  Either way, the concept is fundamentally the same. 

Scholars today ask a key question that must have crossed the minds of Roman soldiers shivering through long watches in the English rain: What were they doing there in the first place? The scale of the wall and its system of ditches, ramparts, and roads suggest that the enemy could be deadly.

The Resource Extraction Game: Imperial Maintenance versus Overreach 

Prototype of Roman bathhouse: a small model of such a bathhouse could consume roughly 250,000 trees per yer (for fuel).  The city of Rome alone had over 900 documented bathhouses.  The implications for environmental degradation would obviously be huge, for the Italian Peninsula and beyond.   

The reasons for occupying far-flung territories should not be too difficult to figure out.  Roman soldiers were occupying lands on the periphery of their empire for the same reasons that Empires have almost always sought to occupy: they were facilitating the extraction of relatively cheap natural resources, to fuel their own growth and development.  First and foremost among these resources: the land itself in tandem with the “commodities” or “inputs” which grew atop it—most especially people and timber.  Both people (as both slaves and potential future soldiers) and timber (as both construction material and fuel) represented concentrated forms of energy which, if handled properly, could be used and leveraged by the imperial system, to fuel still more growth. 

The culture of the Roman Imperial Army up to this time was merely a refraction of this longer term symbiotic process of resource extraction, growth in systemic complexity and sophistication, and subsequent physical expansion of Imperial domain.   Again, I emphasize the very human concept of “culture” here, because human beings have a tendency to configure their shorter-term social arrangements around longer-term systems of matter and energy extraction.  Once again, in the realm of human culture, form follows function.   Furthermore, a disruption in one area can easily lead to disruptions in the other.  This would be clearly demonstrated in the Empire’s Crisis of the Third Century, the subsequent radical reforms of Diocletian, Constantine and others, and the gradual collapse and transition of the western branch of the Empire, toward the end of the 5^th century, CE. 

Would the astute Emperor Hadrian have likely had a clear vision of what lay ahead for the Empire over the next several decades?  Probably not.  But, his administrative behavior does suggest that he correctly saw that the Empire would have to change its course, starting with military policy, if it was to survive in some form in the future.     

Military bases were often ad hoc installations set up to watch rivers and other key supply routes. The Latin word for frontier, limes (LEE-mess), originally meant a patrolled road or path. We still use the term: Our “limits” comes from limites, the plural of limes.

Roman guard post in northern Europe, as depicted in the film, Centurion.  Such posts were established in order to defend resource extraction points, and supply lines, on the Empire's periphery.  

The Gradual Shift from a Philosophy of Expansion to "Defense-in-Depth"

The Roman Empire circa 125 CE, around the time of Hadrian.  This expansive empire was essentially fueled by a combination of wind, sunlight, rain-fed agriculture, which was then used to feed human and animal muscle power.  

This defensive concept of border patrols would be “perfected” roughly a century and half later, by another astute Emperor-General, Diocletian.  In the late third century, he would label this strategy “defense in depth.”  Any foreign (so called “barbarian”) elements that breached the Imperial border or wall might expect to be temporarily “successful” in pillaging Roman villages or towns deeper within the Empire; however, on their way back out they could likewise also expect to meet well-armed Roman troops ready to face them, block their departure, and possibly annihilate them.  In this regard, Hadrian may be seen as a possible early co-author to the “defense-in-depth” strategy.  The author writes further:

The Roman frontier, in other words, is better seen not as an impervious barrier sealing Fortress Rome off from the world but as one tool the Romans used to extend influence deep into barbaricum, their term for everything outside the empire, through trade and occasional raids.

In other words, the Romans, like many societies which followed after them, used their walls and the “borders” which they supposedly defined as but one means to demarcate their world from the world of outsiders—the barbarians who skirted their boundaries.  Mind you, viewed in isolation, such a border could not keep out a determined and well-equipped foreign army.  The physical border was also conceptual, however.  It was a physical manifestation of an idea: Rome and its boundaries, Rome and its limits. 

The author goes on to make a point which, for me, works better as a rhetorical device than as an actual conveyor of information.  In explaining how those societies bordering on the Empire were eventually able to challenge it, he wrote the following:

While Rome looked the other way, barbarian tribes grew bigger and more aggressive and coordinated. When troops were pulled from across the empire to beat back the Persians, weak points in Germany and Romania came under attack almost immediately.

It was not so much that the Romans chose to “look the other way” as much as they simply did not have the resources (either human or material) in the west, to keep up with changing social, political, and environmental circumstances. 

In the east, it was a somewhat different story: there, the Empire was better endowed with physical resources.  It was significantly richer, in an objective material sense.  Likewise, albeit with fits and starts, eastern Roman leadership showed greater flexibility in adapting itself to evolving social, environmental, and military conditions.  Eastern leadership was less wed to the nostalgic love of the older Roman foot soldier, based on the time-honored legion system.  Instead, in the east, leaders were more willing to adapt to themselves to the more sophisticated, high-speed (and, for the Empire, more expensive) style of warfare that the new horse-mounted archers represented.  But this would mean abandoning much of the “classic” notion of direct, hand-to-hand combat (for which the old legions were so famous, and feared) in favor of newer, long-range artillery fire from fast-moving horse archers.  This was a direct result of Roman leadership taking stock of their losses at the hands of the Huns, in particular, and subsequently deciding to learn how to fight like them. 

This analysis of the dynamic interplay between fixed and mobile military assets is missing from Curry’s analysis altogether.  As such, this remains one of the most glaring weaknesses in his otherwise solid analysis.  The other is, unfortunately, in his conclusion.  Here, the author seems to fall into the same intellectual trap that many historians—both professional and amateur—have fallen into since the time of Edward Gibbon: namely, that with the collapse of the Empire on the Italian Peninsula the entire Roman Empire somehow also mysteriously vanished.  The author writes as follows: 

The empire would never be safe inside its shell again. Pressures on the frontiers finally became too great. Cities across the empire began building their own walls; the emperors scrambled to fight off regular invasions. The costs and chaos were crippling. Within two centuries an empire that once dominated an expanse larger than today’s European Union was gone.

This is historically incorrect, however.  It wasn't gone.  It was merely contracted and transformed.  Contrary to popular intellectual mythology, the Roman Empire did not vanish after the year 476, CE.  Roman civilization would continue on for almost another 1,000 years—based out of the Empire’s eastern capital, at Constantinople (a.k.a., “New Rome”).  There, a continuous and unbroken line of Roman emperors would be crowned, appointed, designated, blessed, baptized, scandalized, and gossiped about (and, in some cases “violently replaced”) just as had always been the case, over previous centuries.  And, just has always been the case, these more eastern-oriented (or "Oriental") Romans would continue to adapt and innovate over long periods of time—learning from both friend and foe alike—in order to survive, and sometimes even thrive.

In this broader context, Emperor Hadrian’s Wall represents just one node in a much larger matrix of long-term experimentation in Roman military, leadership, and resource management styles.  It would be successful for a while, and then, Roman Imperial leadership would have to change strategies yet again, in order to promote the Empire’s long-term prospects of viability.  

By all objective measures of chronology, the Romans were on the whole highly successful.  Furthermore, it may well be that that message of long-term adaptability is the message that Roman civilization might bequeath to us, today, in the early 21^st century.  Such a statement assumes, of course, that there would be people in our era willing and able to listen to such historical echoes.  I am here proposing that we should re-examine the more complete picture (involving a rigorous assessment of both the "Occidental" and "Oriental" Rome) regarding Empire's contribution to world history.  Beyond this, I am also proposing that this be viewed as a kind of "living history," with a highly relevant message of adaptability and sustainability for 21st century civilization.  However, the big challenge now, as with many issues, is in how we choose to frame the situation.  This, in turn, leads us to the challenge of historiography.           

The Final “Barbarian” Invasion: Exactly What—or “Who”—Destroyed the Roman Empire, and Why? 

The Roman Forces under Gen. Belisarius depicted attacking the Vandals in North Africa, circa 533 CE.  This was 1 of 3 major theaters of operation at that time (Persia, Africa, and Italy) known collectively as "The Wars of Justinian" (see the contemporary historian, Procopius, for detials).  These overlapping military campaigns were designed to re-establish the original boundaries of the old Roman Empire.  Something close to this was eventually achieved by the Emperor Justinian for a brief period: however, it was achieved at an astronomical cost in terms of both blood and treasure.   

The Empire was not ultimately destroyed because of some breach of a physical wall.  Nor, as stated previously, was it destroyed because of the Roman Army-backed coup of Odovacer in 476, CE. The last or final act of destruction against the Roman Empire would prove to have more long-term consequences than anything which the Goths, Gepids, Alans, or even the notorious Huns would be capable.  The final, destructive invasion of the Roman Empire came neither by land nor by sea.  

The final invasion of the Roman Empire came initially via 18^th century historical textbook (some would even say as early as 17^th century history books).  It was waged by pen- and paper-wielding western European historians who—for a host reasons—sought to excise the Latter Roman Empire from a larger western European cultural and historical narrative.   

Around this time, a massive project of historical re-framing and re-writing began.  From that time going forward, the surviving portion of the Roman Empire, which had done such an outstanding job at adapting and adjusting to changing world circumstances, would be retroactively re-labeled—by foreigners, no less.  

It would be called “The Byzantine Empire” by these foreigners, the early modern western European historians.  In short, one could argue that the Romans had become the victims of their own success: they had actually become too good at adapting and adjusting to rapidly changing global circumstances.  They had moved their capital city many times, sometimes having more than one at the same time.  They had had anywhere from 1 to 4 concurrent, recognized Emperors. They gradually changed their language.  They gradually changed their religion.  In spite of all this, however, they never ceased being  “Roman.”  However, an eastern-tilting, Asian-influenced Roman Empire may have not been a terribly “convenient” truth, at a time when a more western-oriented, more Eurocentric narrative was in the process of being constructed. 

Let me be painfully clear here: there was never an actually-existing “Byzantine Empire.”  The name “Byzantine Empire” was made up, and applied here as an alternate form of post facto historical entry.  This was a change in label for what had always, previously been known as the latter phases of (indeed, arguably, the latter “half” of) the one and only “Roman Empire."    

Conclusions: History versus Historiography 

Emperor Constantine (center, circa 325 CE): he is generally regarded as having launched the Roman Empire's "Byzantine" phase in the early 4th century.  This would best be described as the "Christian" phase of the Empire.  This period of the Empire's history has often been mistakenly referred to as a distinct "Byzantine Empire," and a successor state to the Roman Empire.  Neither the Romans nor any of their contemporary neighbors ever referred to there being an actually-existing "Byzantine" entity during this period, however.  The Byzantine Empire was a historical fiction-made-real, created by western European historians, consciously seeking to re-label the latter phases of a continuously-evolving, somewhat more Asian-leaning Roman Empire.   

Why is this point (on “historiography,” or the portrayal of history) so important?  Consider the following points: 

·         Like all Empires, the Roman Empire was a multi-national, multi-lingual, and culturally diverse enterprise

·         The “Byzantine” label has been a source of much confusion for students for decades, if not centuries, in terms of how it relates to “Roman” civilization.

·         The “Byzantine” label often has the effect of  cutting off discussion of the “evolved” Roman Empire arbitrarily.

·         Given the above points, the “Byzantine” label can block students or casual readers from understanding the profound nature of an Empire’s ability to adapt to long-term structural change, over nearly 10 centuries.

·         By de-tangling the latter historical phases of the Roman Empire from its now-dysfunctional “Byzantine” label, we would be portraying a people as they had never ceased in portraying themselves—as Roman.  The Christian Church did not somehow cease to be called "Christian" after its formal merger with the Empire; therefore, by what leap of logic did the Roman Empire somehow cease to be "Roman?"        

These points are, in turn, important because they would give us a far broader panorama of actual Roman history.  Furthermore, as we struggle with our own contemporary issues of long-term sustainability and viability (ranging from the political, to the economic, to the cultural, to the environmental), we could look upon Roman civilization, writ-large, in a similar and even more-relevant light today.

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[1] Collapse is not necessarily the same thing as destruction.  Collapse is simply a contraction, and consolidation of functions which can be less complex and/or less frequent.  Of course, the ultimate collapse is would the death or destruction of a system.  Where all forms of destruction are collapses, not all collapses result in destruction.  Indeed, collapse can often take place so as to avoid destruction.  .   

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THE ORIGINAL ARTICLE APPEARS HERE:

Bouncing along a dusty Bavarian logging road, archaeologist Claus-Michael Hüssen keeps his eyes on the tree line to the left, searching for some familiar landmark in the thick forest. Suddenly he pulls the van over and gets out, pausing to pack tobacco into his pipe and consult a 1:50,000-scale survey map.

Head down, pipe in hand, Hüssen—a researcher with the German Archaeological Institute—crosses the road and wades through the thick underbrush. Fifty yards from the road, he nearly misses a low dirt mound about three feet high and six feet across. Littered with flat white stones, it runs in an unnaturally straight line along the forest floor.

Nearly 2,000 years ago this was the line that divided the Roman Empire from the rest of the world. Here in Germany the low mound is all that’s left of a wall that once stood some ten feet tall, running hundreds of miles under the wary eyes of Roman soldiers in watchtowers.

It would have been a shocking sight in the desolate wilderness, 630 miles north of Rome itself. “The wall here was plastered and painted,” Hüssen says. “Everything was square and precise. The Romans had a definite idea of how things should be.” Engineering students measuring another stretch of wall found one 31-mile section that curved just 36 inches.

Hüssen faces north, the Roman Empire at his back. Two hundred yards away, just past a narrow meadow torn up by wild boars and a rushing stream, the next hill rises like a green wall. “Here’s the border,” he says, “and on the other side is a wonderful view of nothing.”

A stunning network of walls, rivers, desert forts, and mountain watchtowers marks Rome’s limits. At its peak in the second century A.D., the empire sent soldiers to patrol a front that stretched from the Irish Sea to the Black Sea as well as across North Africa.

Hadrian’s Wall, in England, probably the best known segment, was named a UNESCO World Heritage site in 1987. In 2005 UNESCO established a combined site with the 342-mile German frontier. Preservation experts hope to add sites in 16 other countries. The international effort may help answer a surprisingly tricky question: Why did the Romans build the walls? To protect a regime besieged by barbarians, or simply to establish the physical edge of the empire?

The question isn’t just academic. Defining and defending borders is a modern obsession too. As politicians have debated building a wall between the United States and Mexico and troops face off across the land-mine-strewn strip of ground between the two Koreas, the realities the Roman emperors faced are still with us. Understanding why the Romans were obsessed with their borders—and the role their obsession played in the decline of the empire—might help us better understand ourselves.

From around 500 B.C., Rome expanded continually for six centuries, transforming itself from a small Italian city-state in a rough neighborhood into the largest empire Europe would ever know.

The emperor Trajan was an eager heir to this tradition of aggression. Between 101 and 117, he fought wars of conquest in present-day Romania, Armenia, Iran, and Iraq, and he brutally suppressed Jewish revolts. Roman coins commemorated his triumphs and conquests.

When he died in 117, his territory stretched from the Persian Gulf to Scotland. He bequeathed the empire to his adopted son—a 41-year-old Spanish senator, self-styled poet, and amateur architect named Publius Aelius Hadrianus. Faced with more territory than Rome could afford to control and under pressure from politicians and generals to follow in the footsteps of his adoptive father, the newly minted emperor—better known as Hadrian—blinked. “The first decision he made was to abandon the new provinces and cut his losses,” says biographer Anthony Birley. “Hadrian was wise to realize his predecessor had bitten off more than he could chew.”

The new emperor’s policies ran up against an army accustomed to attacking and fighting on open ground. Worse, they cut at the core of Rome’s self-image. How could an empire destined to rule the world accept that some territory was out of reach?

Hadrian may simply have recognized that Rome’s insatiable appetite was yielding diminishing returns. The most valuable provinces, like Gaul or Hadrian’s native Spain, were full of cities and farms. But some fights just weren’t worth it. “Possessing the best part of the earth and sea,” the Greek author Appian observed, the Romans have “aimed to preserve their empire by the exercise of prudence, rather than to extend their sway indefinitely over poverty-stricken and profitless tribes of barbarians.”

The army’s respect for Hadrian helped. The former soldier adopted a military-style beard, even in official portraits, a first for a Roman emperor. He spent more than half of his 21-year reign in the provinces and visiting troops on three continents. Huge stretches of territory were evacuated, and the army dug in along new, reduced frontiers. Wherever Hadrian went, walls sprang up. “He was giving a message to expansion-minded members of the empire that there were going to be no more wars of conquest,” Birley says.

By the time the restless emperor died in 138, a network of forts and roads originally intended to supply legions on the march had become a frontier stretching thousands of miles. “An encamped army, like a rampart, encloses the civilized world in a ring, from the settled areas of Aethiopia to the Phasis, and from the Euphrates in the interior to the great outermost island toward the west,” Greek orator Aelius Aristides noted proudly, not long after Hadrian’s death.

That “outermost island” was where Hadrian built the monument that bears his name, a rampart of stone and turf that cut Britain in half. Today Hadrian’s Wall is one of the best preserved, well-documented sections of Rome’s frontier. Remnants of the 73-mile barrier run through salt marshes, across green sheep pastures, and for one bleak stretch not far from downtown Newcastle, alongside a four-lane highway. Miles of it are preserved aboveground, lining crags that rise high above the rain-swept countryside.

More than a century of study has given archaeologists an unparalleled understanding of Hadrian’s Wall. The wall, perhaps designed by Hadrian himself on a visit to Britain in 122, was the ultimate expression of his attempt to define the empire’s limits.

In most places the stone wall was an intimidating 14 feet tall and 10 feet wide. Traces of a 9-foot-deep ditch running the length of the wall are still visible today. In the past few decades excavations have uncovered pits filled with stakes between ditch and wall, one more obstacle for intruders. A dedicated road helped soldiers respond to threats. Regularly spaced gates were supported by watchtowers every third of a mile.

A couple miles behind the wall, a string of forts was evenly spaced half a day’s march apart. Each fort could house between 500 and 1,000 men, capable of responding quickly to any attacks. In 1973 workers digging a drainage ditch at Vindolanda, a typical frontline fort, uncovered piles of Roman trash under a thick layer of clay. The wet layer held everything from 1,900-year-old building timbers to cloth, wooden combs, leather shoes, and dog droppings, all preserved by the oxygen-free conditions.

Digging deeper, excavators came across hundreds of fragile, wafer-thin wooden tablets covered in writing. They provide day-to-day details of life along Hadrian’s Wall: work assignments, duty rosters, supply requests, personal letters. There is even a birthday party invitation from one officer’s wife to another, the earliest surviving example of women’s handwriting in Latin.

The tablets suggest that watching over the “wretched little Britons,” as one Vindolanda writer describes the locals, was no picnic, but the fort wasn’t exactly a hardship post. Some soldiers lived with their families—dozens of children’s shoes, including baby booties, are among the footwear recovered. And the wall’s patrollers ate well: Bacon, ham, venison, chicken, oysters, apples, eggs, honey, Celtic beer, and wine were on the menu. There was even garum, a fermented fish concoction that was the Roman version of Worcestershire sauce. Homesick soldiers received care packages too. “I have sent you ... socks ... two pairs of sandals and two pairs of underpants,” writes one concerned correspondent.

Scholars today ask a key question that must have crossed the minds of Roman soldiers shivering through long watches in the English rain: What were they doing there in the first place? The scale of the wall and its system of ditches, ramparts, and roads suggest that the enemy could be deadly.

Yet reports from Vindolanda hardly portray a garrison under pressure. Aside from a few scattered clues—like the tombstone of luckless centurion Titus Annius, who was “killed in the war”—there are no direct references to fighting anywhere on the British frontier. The big building project to the north isn’t even mentioned. “You get a sense something’s up. Colossal amounts of supplies are being ordered,” says Andrew Birley, director of excavations at Vindolanda and Hadrian biographer Anthony Birley’s nephew. “But they don’t refer to the wall itself.”

If the walls weren’t under constant threat, what were they for? By bringing the sheer scope of the Roman frontier into focus, the effort to create a multinational UNESCO heritage site may help answer the question. Ever since British antiquarians organized the first scientific excavations along Hadrian’s Wall in the 1890s, historians and archaeologists have assumed Rome’s walls were military fortifications, designed to fend off barbarian armies and hostile invaders.

For decades arguments focused on tactical details: Did soldiers stand along the wall to rain spears and arrows down on invaders or sally forth to engage the enemy in the field? The trenches of WWI—and the deadly back-and-forth battling of WWII—did little to change the prevailing view of the ancient frontier as a fixed barrier separating Rome from hordes of hostile barbarians.

Archaeologists studying the frontiers in the 1970s and ’80s later found that the Iron Curtain dividing Europe had shadowed their view of the distant past. “We had in Germany this massive border, which seemed impenetrable,” says C. Sebastian Sommer, chief archaeologist at the Bavarian State Preservation Office. “The idea was here and there, friend and foe.”

Today a new generation of archaeologists is taking another look. The dramatic, unbroken line of Hadrian’s Wall may be a red herring, a 73-mile exception that proves an entirely different rule. In Europe the Romans took advantage of the natural barriers created by the Rhine and Danube Rivers, patrolling their waters with a strong river navy. In North Africa and the eastern provinces of Syria, Judaea, and Arabia, the desert itself created a natural frontier.

Military bases were often ad hoc installations set up to watch rivers and other key supply routes. The Latin word for frontier, limes (LEE-mess), originally meant a patrolled road or path. We still use the term: Our “limits” comes from limites, the plural of limes.

Outposts on rivers like the Rhine and Danube or in the deserts on Rome’s eastern and southern flanks often resemble police or border patrol stations. They would have been useless against an invading army but highly effective for soldiers nabbing smugglers, chasing small groups of bandits, or perhaps collecting customs fees. The thinly manned walls in England and Germany were similar. “The lines were there for practical purposes,” says Benjamin Isaac, a historian at Tel Aviv University. “They were the equivalent of modern barbed wire—to keep individuals or small groups out.”

Isaac argues that the frontiers resembled certain modern installations more than thick-walled medieval fortresses: “Look at what Israel’s building to wall off the West Bank. It’s not meant to keep out the Iranian army, it’s made to stop people from exploding themselves on buses in Tel Aviv.” Warding off terrorists may not have motivated the Romans, but there were plenty of other factors— as there are today. “What the United States is planning between itself and Mexico is substantial,” says Isaac, “and that’s just to keep out people who want to sweep the streets in New York.”

More archaeologists are endorsing that view. “Isaac’s analysis has come to dominate the field,” says David Breeze, author of the recent Frontiers of Imperial Rome. “Built frontiers aren’t necessarily about stopping armies but about controlling the movement of people.” The Roman frontier, in other words, is better seen not as an impervious barrier sealing Fortress Rome off from the world but as one tool the Romans used to extend influence deep into barbaricum, their term for everything outside the empire, through trade and occasional raids.

For centuries emperors used a mix of threats, deterrence, and outright bribery to secure peace. Rome negotiated constantly with tribes and kingdoms outside its frontier. Diplomacy created a buffer zone of client kings and loyal chieftains to insulate the border from hostile tribes farther afield. Favored tribes earned the right to cross the frontier at will; others could bring their goods to Roman markets only under armed guard.

Loyal allies were also rewarded with gifts, weapons, and military assistance and training. Friendly barbarians sometimes served in the Roman army; after 25 years, they retired as Roman citizens, free to settle anywhere in the empire. Vindolanda alone was home to units recruited from what are now northern Spain, France, Belgium, and the Netherlands. Iraqi bargemen once sailed England’s rivers under the banner of Rome, and Syrian archers watched over the bleak countryside.

Trade was also a foreign policy tool: The Roman-Germanic Commission in Frankfurt, part of the German Archaeological Institute, has a database of more than 10,000 Roman artifacts found beyond the limes. Weapons, coins, and goods like glass and pottery show up as far away as Norway and modern-day Russia.

Roman foreign policy wasn’t all carrots. Revenge was also a favorite tactic, and the legions were eager to take the fight beyond the frontier.

They spent seven years avenging one disastrous defeat suffered in A.D. 9 in Germany. The historian Tacitus explains that when victorious on the battlefield, General Germanicus “took his helmet off his head and begged his men to follow up the slaughter, as they wanted not prisoners, and the utter destruction of the nation would be the only conclusion of the war.”

Hadrian lashed out at troublesome populations too. In 132 he suppressed a Jewish revolt in a ruthless, protracted campaign. One Roman historian claimed the fighting left half a million Jews dead and added, “As for the numbers who perished from starvation, disease, or fire, that was impossible to establish.” Survivors were enslaved or expelled. The name of the province was changed from Judaea to Syria-Palaestina to wipe away all traces of the rebellion.

Word of such brutality surely made Rome’s enemies think twice before crossing the line. To the Romans, slaughter and genocide were an important part of keeping the empire secure. “The Pax Romana isn’t simply won after a series of battles,” says Newcastle University archaeologist Ian Haynes. “Rather, it’s asserted over and over in brutal ways.”

Just as Hadrian’s Wall shows the Roman frontier at its strongest, an abandoned fortress on the Euphrates River vividly captures the moment the borders began to collapse. Dura-Europos was a fortified city on the frontier between Rome and Persia, its greatest rival. Today Dura sits about 25 miles from the Syrian border with Iraq, an eight-hour bus ride through the desert from Damascus. It first came to light in 1920, when British troops fighting Arab insurgents accidentally uncovered the painted wall of a Roman temple. A team from Yale University and the French Academy put hundreds of Bedouin tribesmen to work with shovels and picks, moving tens of thousands of tons of sand with the help of railcars and mine carts. “At times it was like the Well of Souls scene from Indiana Jones,” says University of Leicester archaeologist Simon James.

Ten years of frenzied digging uncovered a third-century Roman city frozen in time. Fragments of plaster still cling to mud-brick and stone walls, and the rooms of palaces and temples—including the world’s oldest known Christian church—are tall enough to walk through and imagine what they looked like when they had roofs.

Founded by Greeks around 300 B.C., Dura was conquered by the Romans nearly 500 years later. Its tall, thick walls and perch above the Euphrates made it a perfect frontier outpost. The northern end was walled off and turned into a Roman-era “green zone” with barracks, an imposing headquarters for the garrison commander, a redbrick bathhouse big enough to wash the dust off a thousand soldiers, the empire’s easternmost known amphitheater, and a 60-room palace suitable for dignitaries “roughing it” in the hinterlands.

Duty rosters show at least seven outposts reported to Dura. One of the outposts was staffed by just three soldiers; another lay nearly a hundred miles downstream. “This was not a city under constant threat,” James told me when I visited, before the political situation in Syria deteriorated and made excavation impossible. We sat amid the ruins and watched orange gas flares from Iraqi oil wells flicker on the horizon. “Soldiers here were probably busier policing the locals than defending against raids and attacks.”

The quiet didn’t last. Persia emerged as a major threat along the empire’s eastern border a half century after the Romans seized Dura. Beginning in 230, war between the rivals raged across Mesopotamia. It was soon clear the frontier strategy that had served Rome for more than a century was no match for a determined, sizable foe.

Dura’s turn came in 256. Working with a Franco-Syrian team of archaeologists interested in the site’s pre-Roman history, James has spent ten years unraveling the walled city’s final moments. He says the Romans must have known an attack was imminent. They had time to reinforce the massive western wall, burying part of the city—including the church and a magnificently decorated synagogue—to form a sloping rampart.

The Persian army set up camp in the city cemetery, a few hundred yards from Dura’s main gate. As catapults lobbed stones at the Romans, the Persians built an assault ramp and dug beneath the city, hoping to collapse its defenses. Dura’s garrison struck back with tunnels of their own.

As fighting raged on the surface, James says, a squad of 19 Romans broke through into a Persian tunnel. A cloud of poison gas, pumped into the underground chamber, suffocated them almost instantly. Their remains are some of the oldest archaeological evidence of chemical warfare. James believes the bodies, found 1,700 years later, stacked in a tight tunnel, were used to block the tunnel while the Persians set it on fire.

The Persians failed to topple Dura’s wall but eventually succeeded in taking the city, which was later abandoned to the desert. Surviving defenders were slain or enslaved. Persian armies pushed deep into what had been Rome’s eastern provinces, sacked dozens of cities, and overpowered two emperors before capturing a third, the hapless Valerian, in 260. The Persian king, Shapur, reportedly used Valerian as a footstool for a while, then had him flayed and nailed his skin to a wall.

The crisis was a turning point. Around the time Dura fell, the careful balance of offense, defense, and sheer intimidation along the frontier fell apart.

For nearly 150 years the border had helped Rome ignore a painful reality: The world beyond the walls was catching up, in part thanks to the Romans themselves. Barbarians who served in the Roman army brought back Roman knowledge, weapons, and military strategy, says Michael Meyer, an archaeologist at Berlin’s Free University.

While Rome looked the other way, barbarian tribes grew bigger and more aggressive and coordinated. When troops were pulled from across the empire to beat back the Persians, weak points in Germany and Romania came under attack almost immediately.

Hadrian’s legacy was doomed. “The tragic point of their strategy is that the Romans concentrated military force at the frontier,” Meyer says. “When the Germans attacked the frontier and got in behind the Roman troops, the whole Roman territory was open.” Think of the empire as a cell, and barbarian armies as viruses: Once the empire’s thin outer membrane was breached, invaders had free rein to pillage the interior.

The inscription on a five-foot-tall altar uncovered in Augsburg by German workers in 1992 is a sort of epitaph for Hadrian’s grand idea, noting that on April 24 and 25,A.D. 260, Roman soldiers clashed with barbarians from beyond the German frontier. The Romans prevailed—barely.

Their commander set up an altar to Victory. Reading between the lines reveals a different picture: The barbarians had been raiding deep into Italy for months and were heading home with thousands of Roman captives. “It shows the border is already collapsing,” says the German Archaeological Institute’s Hüssen.

The empire would never be safe inside its shell again. Pressures on the frontiers finally became too great. Cities across the empire began building their own walls; the emperors scrambled to fight off regular invasions. The costs and chaos were crippling. Within two centuries an empire that once dominated an expanse larger than today’s European Union was gone.