In the year 376, tens of thousands of Goths arrived on the left bank of the Danube seeking entrance into the Roman Empire.  The petitioners included women, children, and the aged plus perhaps twenty thousand warriors.  They had loaded up their wagons to carry all the provisions and household goods that they could bring with them.

The Rhine and the Danube formed the natural boundaries of the Roman Empire in Europe but there was plenty of cross-border activity.  Some of this was friendly, as when Roman garrisons purchased supplies from their Germanic neighbors.  Yet, many people living on the German side of the rivers were tempted to raid the richer Roman side.  The Romans would cross a river now and then to punish the offenders while practicing rough diplomacy by rewarding favored leaders over troublemakers.

In the past, the Goths had lived far to the east.  In the third century, Goths living north of the Black Sea had raided Roman territory on the sea’s south shore.  In the century that followed, the Goths moved west.  In the 360s, Roman armies crossed the Danube to conduct punitive raids on miscreant Goths north of the river.

This was not the first time that non-Romans had sought entry into the Empire.  When the Romans granted a right of entry to foreigners, they did so with tight controls.  The price of admission was the draft of a designated number of young men into the army and the dispersal of the rest of the population to locations chosen by Rome.  The migrants were not permitted to retain a separate identity within the Empire.

The entrance of the Goths into the Roman Empire in 376 did not follow this pattern.  The Romans admitted half of the Goths as a group.  (Two different political groupings– the Tervingi and the Greuthungi – had sought entry.  Only the Tervingi were admitted.)  These Goths rolled into the Balkans and started living off the land.

Roman propaganda presented their arrival as a godsend.  By admitting the Goths, the (eastern) emperor Valens would gain the Goths’ manpower and their wealth.  Why, then, did the emperor admit only one of the clans, leaving the other to fend for themselves on the far side of the Danube?  (The Greuthungi forced their way across anyway.) The official Roman account of the incident omitted the detail that the main body of the eastern army was off in the desert fighting the Persians.

The entry of the Goths onto Roman territory was a turning point.  After 376, there would be at least one foreign force operating inside the Roman Empire against the will of the government.  It’s one of those odd coincidences that exactly one hundred years later the last western emperor would be deposed.

Were Rome’s borders leaking because of internal rot that disabled the Empire?  Or was the catastrophe the result of happenstance and a thick slice of bad luck?  Should we look to internal factors or external events to explain the one-hundred-year span that began with Goths on the Danube in 376 and ended with the dissolution of the central imperial government in the west in 476?  Edward Gibbon is the foremost example of the “internal rot” school.  Peter Heather is a contemporary historian who can meet Gibbon on his own ground as he makes a strong case – I think an overwhelming case – that outside factors are the chief explanation for the collapse.

Gibbon begins his history around 200 AD and concludes it with the fall of the Eastern Roman Empire when Ottoman Turks took the city of Constantinople (Istanbul) in 1453.  When I got to the last western emperor in 476, I put Gibbon aside for a while.  I may return later to read through to the bitter end in 1453.  When I stopped reading, my Kindle showed I was 30% of the way through the entire work.  That’s one measure of the monumental size of the project that Gibbon took on when he began his study in the mid-1760s.  The first volume of his masterwork was published in 1776, the last in 1788.

Three features in particular characterize the work: his use of sources; his writing style; his stern judgment upon the character of the individuals whose lives he chronicles.  He used primary source material whenever it was available.  He appears to have read everything, ancient and modern, primary and secondary, that there was to read on his subject.  It’s a measure of the educational level of his contemporary audience that he will sometimes quote extensive passages in Latin without offering a translation.  He didn’t think his readers needed one.

His style is distinctive, notable for its detached, Olympian posture.  He makes the elements of his sentences do extra work in a way that is all his own.  Four examples:

Speaking of the Greeks (a people he refers to as Grecians, just as George W. Bush did):

They had too much taste to relinquish their language, and too much vanity to adopt any foreign institutions.  Still preserving the prejudices, after they had lost the virtues, of their ancestors, they affected to despise the unpolished manners of the Roman conquerors, whilst they were compelled to respect their superior power and wisdom.

 

His evaluation of a Roman matron who was married to one emperor and the mother to another:

 

Her amiable qualities never made any deep impression on the dark and jealous temper of her husband; but in her son’s reign, she administered the principal affairs of the empire, with a prudence that supported his authority, and with a moderation that sometimes corrected his wild extravagancies [sic].

 

Comparing the respective importance of iron and precious metals to human progress:

 

Money, in a word, is the most universal incitement, iron the most powerful instrument, of human industry; and it is very difficult to conceive by what means a people, neither actuated by the one, nor seconded by the other, could emerge from the grossest barbarism.

 

Finally, a small joke.  Speaking of an emperor (Gordian II) who came to the throne as a young man and was murdered for his trouble:

 

Twenty-two acknowledged concubines, and a library of sixty-two thousand volumes, attested the variety of his inclinations; and from the productions which he left behind him, it appears that the former as well as the latter were designed for use rather than for ostentation.

 

He must have chuckled as he sharpened his quill after writing that one.

 

Gibbon was a man of strong opinions who did not only report events.  He keeps the reader advised of his evaluation of the moral qualities of the actors upon the historical stage.  On his view, the empire began to fall when it adopted Christianity as the state religion in the first half of the fourth century.  Funds that might have been devoted to public works and to social improvement instead supported the state-sponsored church.  Taxation to pay for the state religion diverted funds away from the army, while the fighting spirit that had formerly fueled Rome’s expansion was wasted on civil war and excessive love of luxury.  The public spirit that had built a massive empire dissolved into the pursuit of office for private gain and dissipation.

Peter Heather can answer each of these points, but the biggest difference between the two comes from a more fundamental question.  Where Gibbon asks why the Roman empire collapsed, Peter Heather asks how did it last as long as it did.  At a time when there were no telecommunications, when the horse provided the fastest available ground transport, when banking, credit, data management, and administration were in primitive conditions, the Roman empire ruled some 70,000,000 people in Europe, Africa, and Asia.  It included all of Europe west of the Rhine and south of the Danube plus modern England and Wales.  Rome ruled northern Africa, including Egypt, from the Mediterranean south to the desert.  In Asia, the empire included modern Turkey, Armenia, Syria, Israel, Jordan, Sinai, and part of Iraq.

Heather estimates that the civilian administrators who managed the Roman Empire numbered perhaps 6,000 at their peak in the fifth century.  At the time the Goths crossed the Danube, the army might have been as large as 600,000 men, although some estimates are as low as 400,000.  Something less than one percent of the Empire’s population managed to protect and administer a vast domain using technology little better than what was available to the Babylonians.

Heather’s thesis is that this enterprise might have continued indefinitely.  In the third century, Rome faced a challenge from a revived Persian Empire.  Significant military losses had caused Rome to reform its finances and to rebuild its military.  Those efforts had been a success.  In the fourth century, the Roman army’s record against Persia had improved, although Persia was still a threat and won some important victories.  According to Heather, when the Goths arrived on the Danube in 376, the Roman Empire was in decent shape to withstand the emerging threat of large numbers of Germanic peoples on the move.

He does not believe that Christianity played a role in bringing down the Roman Empire.  The funds that were devoted to Christian endeavors had previously been spent on pagan temples and monuments.  Economically, Rome was as prosperous in the fifth century as it had ever been.  There was an agricultural boom going on in many parts of the Empire.  (That information is derived from archaeological studies that were not available to Gibbon.)

The empire enjoyed the deep loyalty of the elites who benefited from Roman citizenship.  Rome was a one-party state where violent death was the standard method for dealing with political opposition.  Throughout the empire’s history, with no established constitutional method for transferring power, there were frequent bloody struggles to get or to keep power.

Still, most of the Roman elite sought prestige, acclaim, and wealth rather than political power.  High-born Romans who could suppress a thirst for political power could enjoy a life of spectacular wealth, leisure, and refinement.  This upper ten percent or so saw Roman civilization as a model of how life should be lived.  They saw themselves as an example to the rest of humankind.  Before the conversion to Christianity, elite Romans believed they had been selected by the gods to achieve this mission.  After the conversion, they believed that it was God who had picked them.  It was the same ideal either way, and the change in the deity’s identity doesn’t appear to have been debilitating to the everyday functioning of Roman society.

On this view, Roman civilization was a success because it was able to deliver to its elites a version of the good life that they all shared.  While it was a one-party state that used violence to maintain political power, it did not require force to maintain the devotion of the elites who controlled the empire’s wealth.  There was no reason in 376 to think that things were going to start to unravel.  According to Heather, what brought the western empire down were forces acting outside the Empire’s borders plus some bad luck.

The Huns got the process rolling in the 370s.  Originally from the Steppe, the Huns began moving west in the middle of the fourth century.  They impacted Rome even when they were hundreds of miles east of the empire’s border.  In fact, Heather’s thesis is that the Huns did less damage when they were Rome’s neighbor – roughly the mid-430s to the mid-450s – than in the decades when they were moving towards Rome and in the brief period after 453 when Hunnic power collapsed.

It was the Huns who drove tens of thousands of Goths to the Danube at a moment when the eastern Roman army was off fighting Rome’s main enemy, Persia.  Now that hungry Goths were inside the Empire, the Roman plan was to temporize for the short term and then destroy the Goths in battle or by ambush and attrition as the opportunity arose.  The Roman plan to destroy the Goths was to have reached its climax in August 378.  The Goths were busy consuming the production of a large area of the Balkans, administered by the eastern empire.  They needed food and took it from the yeoman farmers of the Roman Balkans.

The eastern emperor, Valens, had made peace with Persia so that he could bring Roman military power to bear against these troublesome Goths.  By this time the Goths had wandered south and east to the vicinity of the town of Hadrianople.  The Roman plan was to catch the Goths in a vice.  Valens brought his army into the vicinity of the town of Hadrianople, facing Goths to the west.  The western emperor, Valens’s nephew Gratian, was to have brought an army from the western empire to the same location, attacking the Goths from the east.  But Gratian had been delayed by a disruption on the Rhine.  He was on his way, but Valens didn’t know where he was.

Valens faced a tough decision.  Half of his military advisors thought he should wait for Gratian.  The others thought an immediate attack was advisable.  This was the finest professional army the world had known to that point in time.  Yet the intelligence available to them was not good enough to support a decision either way.

The situation reminds me of what George A. Custer faced on the day before the Battle of the Little Bighorn.  He knew that his side had massive reinforcements available in the vicinity, but he wasn’t sure where they were and he didn’t have an easy way to communicate with them.  The enemy was directly in front of him.  He didn’t want them to get away.  He was sure his forces were superior.  He underestimated the size and quality of the force he faced.

The deciding factor may have been that Valens didn’t want to share the glory of the coming victory with his nephew.  On August 9, 378, he marched his army 12 miles in the hot sun to attack the Goths.  The terrain did not allow the Romans room to deploy their most effective tactics.  The Goths were thicker on the ground than the Romans had expected.  The eastern Roman army was routed.  Valens died in the course of the massacre of the troops under his command.

Rome and the Goths made peace in 382.  The Goths remained a coherent and viable nation inside the Empire.  In fact, when the end came, the first non-Roman king of Italy, the man who deposed the last emperor, was a Goth, although not from the branch of the Gothic nation that won at Hadrianople.

Even after Hadrianople, no one on the Roman side figured that the Goths were the thin end of a wedge that would lead to the collapse of the western empire.  Contemporary Romans continued to believe that the biggest threat to the empire came from Persia, not from the Germanic peoples of Europe.

After two tribes of Goths became a permanent feature of Roman political life, troubles boiled up every thirty years or so.  The period 405 to 410 saw the unfolding of four separate calamities.  Another wave started in the 430s and continued to the mid-450s.  A last Roman effort in 468 to retrieve the situation failed, leading to the end of imperial government in the west when the last German thrust came in 476.

That’s not to say that things were calm between outbreaks.  There were frequent civil wars over succession.  Provincial armies would rebel when they felt they were being disrespected by the central authority.  The power that went with the imperial purple attracted many who were willing to risk everything to gain it.  Heather’s argument is that these political crises strained the Empire but were not enough to bring it down.

The powerful point that seals his argument is this: the Eastern Roman Empire survived for a millennium after the fall of the west, during which it practiced Christianity as a state religion while facing crises of succession and challenges to the legitimacy of the emperor of the day, just as the western empire had done.  The eastern empire did not possess moral qualities superior to those of the west.  If internal rot was the cause of the collapse, why did the eastern empire survive?  I don’t know if Heather is the first historian to make this point. It was a palm-to-forehead moment when I first read it.

The story of the unraveling can be told without reference to any internal moral decay.  The catastrophe can be explained as the unfolding of the fortunes of war and the twists and turns of international politics and diplomacy.

As the fourth century ended, the Huns again shifted further west.  They engaged directly with the eastern empire in the Caucasus and they put fresh pressure on the Germanic peoples to the west.  If you were in the path of the Huns, your options were flight or surrender.  The Germans who escaped from the Huns produced another set of crises for the western empire in the second half of the first decade of the fifth century.  In 405, a Gothic army invaded Italy from the northwest – not the Goths who entered in 376 – and laid siege to Florence before they were done in by a Roman counterattack.  Tens of thousands of Vandals, Suevi, and Alans poured over the Rhine at the end of 406.  They had a merry time consuming whatever wasn’t nailed down in Gaul.  Then, to stay out of the way of the Roman army, the Vandals and their friends crossed the Pyrenees and settled for a time in Spain.  They divided the peninsula among themselves.  Meanwhile, Burgundians moved into a pleasant slice of eastern Gaul.

The capstone of the troubles of the “aughts” of the fifth century was the sack of Rome by the Goths in 410.  These were the Goths who had crossed the Danube in 376.  The two polities had formed into one supergroup, known as the Visigoths, that also included the remnants of the Gothic invaders of 405.  They had never been happy with the peace settlement of 382.  In 410, they were still looking for a permanent place to call their own and they were still being put off by the Roman government.

The Visigoths, united under a king named Alaric, had a long list of demands that they gradually whittled down in an effort to get the Roman government to grant them a place to settle.  They tried playing the Roman Emperor, sitting in Ravenna, against the Senate, still sitting in Rome.  When Alaric couldn’t get a decision out of either of them, he threatened to sack the City of Rome itself.  When the government failed to respond, the Goths moved into the city and looted it.

Both Gibbon and Heather agree that this was not a sack in the usual sense of the term.  There was minimal loss of life.  Christian Goths would lead nuns to safety before ransacking their churches.  The sack was part of a larger negotiation by which Alaric was attempting to find a permanent home for his people.  Alaric died in 411. The Goths had to wait until 418 for their long-desired permanent home.  They were settled in southwestern Gaul.  No doubt remnants of Gothic blood flow in the veins of the vintners and wine merchants of Bordeaux.

Even though the sack of Rome in 410 did not feature heavy doses of murder and assault, unlike the previous sack in the year 390 B.C., 800 years earlier, or the one that was coming in 455, the event demonstrated to contemporaries that the threats to the western empire had grown significantly from the problem presented by the arrival of the Goths in 376.  After the sack, the emperor of the day sent a letter to Britain telling its citizens that they could no longer look to the Roman army to defend them.  Britain was gone or going, Spain wasn’t producing any tax revenue, large segments of Gaul were under foreign control, and parts of Italy had been damaged by two different Gothic attacks.  Things threatened to spin out of control.

A political and military leader named Flavius Constantius helped pull things together against the odds.  He created an alliance with the Visigoths and with their help he started to reconquer the Iberian Peninsula from the Vandals, Suevi, and Alans.  He unfortunately died in 422, leaving a leadership vacuum in the west that lasted into the 430s.

His success against the Vandals and their friends led to the next major crisis.  The survivors of the Roman counterattack joined with the Hasding Vandals, who had avoided an encounter with Roman troops, to form a new Vandal supergroup.  They decided that their hold on Spain was insecure and couldn’t last.  They decamped to North Africa in 427.

Meanwhile, the last great hero of the western empire, a man named Flavius Aetius, came to power in 433.  He effectively recaptured Gaul for Rome.  With the Vandals and friends mostly out of Spain, things were once again looking up for the western empire.

As the 430s closed and the 440s opened, the next round of crises arrived right on schedule.  The Vandals had been granted land in the western provinces of Roman Africa, where, it was hoped, they wouldn’t create any more trouble.  They wanted more.  They moved east in the late 430s and in 439 captured the city of Carthage.  This was the second city of the western empire, a massive port that supplied grain to Rome.  With Carthage gone, the west would starve.

The two halves of the empire planned an invasion to dislodge the Vandals.  A huge armada of naval and land forces was assembled in Sicily in 441 to invade Africa and reclaim Carthage.  The attack had to be called off.  The Huns had arrived on the Hungarian plain and were invading the Balkans.  It would take some 25 years to organize another expedition.

The Huns were approaching the peak of their power.  They were under new leadership from two brothers, Attila and Bleda, who had inherited power from their uncle around 440.  As Heather explains it, a Hunnic leader got and kept power by leading his troops to fresh conquests, receiving tribute from conquered peoples, and distributing a large share of the goods to his followers.  Every success resulted in more people within the Hunnic tent.  To keep the leaders of the new members of the club happy, more conquests were needed.

That may explain why the Huns kept moving west.  Their early victims would have been farmers and shepherds out on the Steppe.  There is only so much lucre to be gained from people who earn their living that way.  The peoples of the area north of the Black Sea would have offered better value.  When the Huns encountered the Roman Empire, first in the east, later in the west, they had hit the motherlode.

The key to the Huns’ success was the design of the bow that was their principal weapon.  They used a recurve design – the tips of the bow pointing away from the archer – but this had been in use for millennia.  Their bows were exceptionally long, ranging from 130 cm (51 inches) to 160 cm (63 inches).  The Huns were mounted archers. A bow that long cannot be used from horseback – the horse’s neck would get in the way.  The Huns found a brilliant solution.  Their bows were asymmetric.  The lower half had a much smaller arc than the upper.

This design allowed a mass of Huns to fire arrows from horseback at a distance.  The enemy’s weapons could not reach them, while the Huns could rain down masses of arrows on their victims.  Eventually, the opposition broke in panic under the stress produced by the flood of arrows.  Once the enemy had broken ranks, the Huns could run in on horseback and pick off individuals or small groups.

By 445, Atilla had eliminated his brother and was the sole ruler of a vast territory.  He had many more mouths to feed than before, but he had found a way to bring thousands of pounds of gold into the Hunnic empire every year.  The eastern empire was prepared to deliver massive quantities of gold, 21,000 pounds in some years – that would be $400,000,000 at 21st-century gold prices – to buy peace.  Atilla distributed that gold to stay in power.  Gold appears in Germanic graves in significant quantities during this period.

Atilla’s record against the western empire was mixed.  He sometimes allied with Rome to attack other groups.  Sometimes he attacked Roman assets.  His army invaded Italy on one occasion, Gaul on another.  The western Romans held their own in battle against Atilla.  They ended his reputation as an invincible force.

Atilla died suddenly in 453.  His sons were not able to keep his enterprise together.  Hunnic power began to collapse.  Heather believes that the Hunnic empire did more damage to Rome by collapsing than it did during the short period when it was Rome’s neighbor.  With the Huns no longer around to control them, the formerly subject peoples were now free to join forces and go on the road to attack Rome.  While the Roman contenders for political power continued the merry game of assassination, civil war, and treachery to determine who would control the high offices of the empire, new waves of Goths, Franks, Alemanni, and others invaded the west.  The Vandals made a visit to Italy and sacked Rome in 455.  Unlike the sack of 410, this one was done with malicious intent.  The Vandals cemented their future place in the English language by looting, plundering, and assaulting at will.

But even after all of this mayhem, the Roman empire was able to function and had a decent shot at a comeback.  The expedition to regain Carthage that was postponed in 441 was laid on in 468.  Some 1,100 vessels, every ship the Romans, east and west, could find, were ready to sail.  Some 50,000 troops were on board.  The plan was to sail to a point near Carthage, form up on land, invade, and retake the city.

The flotilla arrived off a body of land known as Point Bon.  The Roman commander, Basiliscus, chose that spot because it was close to Carthage, leaving the troops a short march to retake the city once they had landed.  In hindsight, a location further away might have been preferable.  An invasion that close to Carthage allowed the Vandals to keep track of Roman dispositions.

Even so, all might have been well.  The Roman navy was positioned on the east side of the Gulf of Tunis.  The prevailing winds in that area at that time of year are easterly.  The wind would allow the Romans to maneuver at will, and would hold off any opposing forces of the Vandals.  As Heather notes, with Carthage and north Africa back in the Roman fold, the western empire might have gone on for centuries.  It would not have been the overpowering force it had been in, say, 350, but it would have been a serious contender for power.

The possibility of Rome’s survival floated away on a changing wind.  A northwest wind, unusual at that time of year, began to blow the Roman ships toward shore.  Roman sailing vessels were square-rigged; the only way they could move into the wind was by oar.  Most vessels weren’t equipped with galleys for rowers.  Even those with galleys had to surrender to an unfavorable wind when the strength of the rowers gave out.

While the Romans were sorting things out, the Vandals used the wind at their backs to launch fire ships into the middle of the Roman fleet.  A wooden sailing vessel has no defense against fire.  The invasion fleet was wrecked in a matter of hours.  The operation was called off.  There was nothing left for the western imperial government to do but wait for the end.

It was another branch of the Goths, the Ostrogoths, who delivered the final blow.  Oddly, the final stroke was a legal maneuver.  The Ostrogothic king, Odoacer, appeared before the Roman Senate with a clever proposal.  He arranged for the Senate to send a letter to the eastern Roman emperor, stating that it had proven cumbersome to have two emperors, one in Italy, the other at Constantinople.  For the future, the Senate would recognize the eastern emperor as the sole imperial authority.  Italian affairs could be managed by an official based in Rome.  They had recognized Odoacer as the King of Italy and they suggested that the emperor do the same.

The last emperor in the west was named Romulus, the same as Rome’s first king, who founded the city in 753 BC according to legend.  Known as Romulus Augustulus (“little Augustus”), the last western emperor was allowed to retire to a castle controlled by the new king.  The date of his death is not known but there is no record of his assassination.  Roman emperors were not replaced peacefully as a rule.  It appears that Odoacer did not think killing Romulus to be worth the trouble.

Odoacer collected the imperial crowns and robes, boxed them up, and shipped them off to the emperor in Constantinople.  The western empire assigned its assets for the benefit of creditors while remaining subject to the technical control of the now sole emperor.  The emperor signed off on the deal and that was that.

Central government ended but some aspects of the Roman way of life continued.  Some, but not all.  The Roman way of life was lived in cities, and the cities started to empty.  The population of the city of Rome fell from over a million (possibly 1.5 million) in the fourth century to 20,000 in the sixth.  Rome had been the first city to achieve a population that large.  The second city to do so was London in the nineteenth century.

But in other places, parts of the Roman way of life continued.  Small villages that were away from the main invasion routes survived.  In some more heavily populated districts, local and regional Roman elites found a way to stay in place.  When there was land left over after the head man of the local invasion force had paid off his followers, Roman landowners could retain a foothold.

Roman law was still applied in many cases and local Roman elites could supply the knowledge and the literacy to help administer government.  Roman coin still circulated.  Churches continued Roman religious traditions and practices.  Henri Pirenne is a historian who argues convincingly that the Mediterranean orientation that was a principal feature of Roman civilization remained after the fall of the central government and continued until Arab invasions closed off the Mediterranean in the seventh and eighth centuries.

Indeed, some historians go further and claim that nothing really “fell” in the late fifth century, that all that happened is that one elite replaced another.  There is precedent for that kind of “fall”.  The Norman invasion of England in 1066 is the prime example.  Several thousand Anglo-Saxon landowners were dispossessed and replaced with a like number of Normans, but the underlying population remained unchanged.

Heather is firm that something more complicated happened in fifth-century Rome.  Many archaeological sites reveal a destruction layer that can be dated to this period.  There is abundant historical and archaeological evidence that significant numbers of Germanic peoples (and others – the Alans were Iranian) crossed the rivers and settled on Roman territory.

One of the real pleasures of reading Professor Heather is his willingness to show his work.  He uses his clear conversational writing style to explain and evaluate the nature of the documentary and physical evidence that underlies his conclusion.  He has a fine sense of humor combined with a deep understanding of the way Roman society operated.  He doesn’t appear to be grinding an axe or advocating an ideology.

In the introduction to “Empires and Barbarians” he gives us a tour of some of the intellectual history that has colored the way historians and anthropologists have studied human migration.  The earliest work in the field was conducted in the nineteenth century by a German archaeologist named Gutav Kossinna.  Herr Kossinna believed that when the archaeological record revealed a significant change – when for example evidence of agriculture is found in a layer above remains left by hunters – the explanation was that agriculturists had invaded space previously occupied by hunters and had eliminated the people that were there when they arrived.  As Heather notes, an equally good explanation might be that hunters had adopted farming without anyone invading, or that farmers moved into ground occupied by a hunting culture and the two lived side by side for a time until the hunters adopted the farming way of life or were gradually replaced.  And so on.

The invasion theory was popular among German academics, so much so that when in the 1930s and 1940s the Germans again took up the old habit of crossing rivers to conduct military operations, they often rearranged boundaries and place names to correspond to their understanding of the lessons taught by archaeology.

After the second world war, academics wanted to disclaim any association with the invasion hypothesis.  Where Kossinna saw a “movement of peoples” his successors saw “elite replacement.”  Kossinna saw migrants leaving an empty spot on the earth at the point where their migration began and destroying or overwhelming the population they encountered in the place they selected for settlement.  The horror that resulted from the implementation of this theory during the National Socialist period of German history led the post-war generation to an interpretation where populations remained largely stable with only the very top slice of the social pyramid undergoing change.

The truth seems to be that the German migrations of the fourth and fifth centuries were not transfers of elites in the manner of 1066.  They were movements of groups that could include up to 100,000 or so individuals, men and women of varied ages and conditions, of whom perhaps 20% were warriors.  At the same time, these were not proto-nations.  Groups formed and re-formed on the fly as they faced opportunities and challenges – from the Romans or the Huns depending on the situation at the time.  Although they did a great deal of destruction and killing, they did not simply wipe out the populations that were in place at their destinations.

Heather also notes that it was the increase over the course of centuries of the complexity and sophistication of German political organization that gave the invaders a chance for success.  It wasn’t internal rot but internal Roman strength that created this final problem for Rome.  Rome set the Germanic peoples a challenge that they were able to meet only after centuries of contact with Rome.  Even so, they needed luck to succeed.  Change a decision by the Roman leadership at Hadrianople in 378, let the African command keep a closer eye on the Vandals as they moved across northern Africa in the 430s, pick a day for retaking Carthage when the prevailing easterly winds held at Point Bon in 468, and the western empire might have endured in some form for centuries.

Sources:

Edward Gibbon, The History of the Decline and Fall of the Roman Empire.  https://www.amazon.com/gp/product/B01H23KONK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Peter Heather, The Fall of the Roman Empire, A New History. https://www.amazon.com/gp/product/B0044KLOXO/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Peter Heather, Empires and Barbarians, The Fall of Rome and the Birth of Europe. https://www.amazon.com/gp/product/B0035KD36U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1