Two questions commonly asked by members of the public are “why did the Romans leave Britain?” and “why did the Roman Empire collapse?”. It is quite easy to give a short answer to the first question, along the lines of “they didn’t leave”, or the slightly longer version “most of them didn’t leave”.

However the only possible short answer to the second question is “there is no short answer”. In fact, it has been estimated that at least 200 different theories have been put forward to explain the end of the Empire.

Having struggled to answer this question myself on many occasions, I decided to do a bit of research. My intention was to produce a brief history of the end of Empire, starting as most such accounts do in 376 and ending with the fall of the Empire in 476. However, my first attempt at this ‘brief’ summary quickly ran to eight pages, so I decided a different approach was called for.

Firstly, I have described below three key events, together with the long term outcome that resulted from them. These illustrate the nature of what was happening and the threats that the Romans faced. Secondly, I have summarised three key reasons why the western Empire collapsed. As far as I can make out (not being a professional historian!) most of the many theories for the end of the western Empire are either variants of one of these, or combinations of them. Though I’m not sure where the one about lead poisoning fits in!

What happened – three key events

The battle of Hadrianople: 09 August 378

In 376, two tribes of Goths crossed the lower Danube into eastern Roman territory. They had both requested permission from the eastern Emperor Valens, and he had granted permission for one of the two groups. Unfortunately through a combination of insufficient troops (Valens was campaigning in Persia) and poor management by the Roman general on the spot the Goths promptly revolted.

It was not until 378 that Valens was able to bring sufficient troops to the Balkans. He requested assistance from the western Emperor Gratian, who obliged but was delayed. Eventually Valens fought the Goths at Hadrianople with Gratian still at least a day’s march away. It is thought that he underestimated the strength of the Goths, and also perhaps that he didn’t want to share the glory with Gratian.

In any case, the battle was a disaster for the Romans. Valens and his army had marched a considerable distance in the summer heat before the battle, but nevertheless were making reasonable progress despite the Goths starting fires that sent heat and smoke onto the Roman lines. The turning point was the sudden (perhaps fortuitous) appearance of the Gothic cavalry on the Roman’s left wing. This caused sufficient confusion and panic for the Romans to be defeated with heavy losses. Valens himself was killed.

From this point on, this group of Goths remained in Roman territory, uniting and becoming what we now know as the Visigoths. They were always looking to achieve a stable deal with the Romans that involved proper recognition for them and land on which to settle. At times they reached peace deals and fought as allies of the Romans. At other times they used military force (including sacking the city of Rome in 410) as part of an attempt to secure a better deal. Ultimately, the Romans never brought them fully under their control. The Visigoths ended up in south-western France and Spain, where they established a Visigothic kingdom after the end of Roman rule.

The Rhine Invaders: 31 December 406

From 406 onwards, several groups entered the Roman empire by force. The first of these was another group of Goths who, though defeated and drafted into the Roman army, eventually rebelled and teamed up with the Visigoths.

The most significant group, however, was a large mixed group of Vandals, Alans and Suevi, who crossed the Rhine into France on New Years Eve 406. They wreaked havoc in Gaul for a couple of years. Initially the western field army was unable to respond due to a shortage of numbers. The lack of a swift response from the centre encouraged a rebellion in Britain, who proclaimed Constantine III as Emperor. He crossed into Gaul in 407 to deal with the Rhine invaders, taking the majority of the British field army with him, never to return. This was effectively the end of Roman rule in Britain (410 is the traditional date) and within a generation Britain had reverted to an Iron Age pre-Roman society.

Constantine III was successful enough to force the Rhine invaders down into Spain where they took control of the Roman provinces. The Empire then began to recover, first eliminating Constantine III and re-establishing central control in Gaul. They then achieved considerable success in subduing the Rhine invaders in Spain. The remaining Rhine invaders then effectively united under Vandal rule and crossed to North Africa in 429. By 440 they had taken control of the Roman provinces in Africa (though not Egypt), thereby depriving the west of a significant source of tax revenues.

As a footnote, the Burgundians followed the Vandals, Alans and Suevi across the Rhine in 411, settling around Mainz. They would later expand their territory and move south into the Rhone Valley, an area that still bears their name. Later on the Franks moved into northern Gaul, establishing a Frankish kingdom which gave the country its modern name.

Attila the Hun invades: 441

Having re-established some semblance of order in Gaul and Spain, the Romans’ next move was to retake the North African provinces from the Vandals. This would restore tax revenues from the province, thereby bolstering the Roman ability to fund further campaigns against the other groups still occupying parts of the western Empire. A joint western and eastern army was assembled ready to sail to North Africa in 441. However, they never sailed, because of the actions of a well-known figure – Attila the Hun.

The Huns had been settled by the Romans in Pannonia (modern Hungary) in the late 420s and early 430s as part of a deal for their support in dealing with the situation in Gaul and Spain. Attila became leader of the Huns in the late 430s, and adopted a much more aggressive attitude towards the Romans. He invaded the Balkans in 441, and it was a direct result of this invasion that the Roman expedition to North Africa was abandoned. He extracted a deal involving payment of 700 lb of gold per year from the eastern Empire which, after a further invasion in 447, was increased to 2100 lb of gold per year.

Attila then turned his attentions to the west. In 451 he invaded Gaul, reaching Paris and Orleans. However, he was defeated and forced to withdraw. In 452 he tried again, this time invading Italy and reaching Milan. This time it was disease and lack of supplies that forced his withdrawal. Attila died soon after in 453 and his Hunnic Empire unravelled remarkably quickly afterwards. The most significant group to emerge from the wreckage of the Hunnic Empire was yet another group of Goths who became known as the Ostrogoths.

The Romans made two further attempts to retake North Africa, in 461 and then again in 468. The first failed when the Vandals crossed to Spain and destroyed the Roman fleet before it could sail. The second didn’t do much better, the Vandals destroying a large part of the Roman fleet off the coast of North Africa before any troops could land.

After this the western Empire simply ran out of steam. Eventually in 476 Odovacer, an Ostrogoth who had joined the Roman army and risen to become a senior officer, took control of what was left of the western Empire (effectively Italy). He decided there was no point having an emperor, and sent the last western Emperor Romulus Augustulus into retirement. He also symbolically sent the ceremonial robes of state back to the eastern Emperor Zeno for safekeeping as they were ‘no longer required’ in the west.

Why did the western Empire collapse – three key reasons

External threat

It is undoubtedly true that the western Empire was invaded on numerous occasions by external forces. Each of the three key events above represents an invasion, firstly by the Goths, then the Vandal/Alan/Suevi coalition, then by the Huns. It is also pretty much certain that the root cause of all of these mass movements was the gradual westward movement of the Huns. This first triggered the migration of the Gothic tribes that resulted in their request to enter the Empire in 376, then the Rhine invasions of 406 onwards and then established the Huns themselves in Pannonia from where they could invade the Empire.

A good case can therefore be made that these migrations represented such a huge influx of ‘barbarians’ into the Empire that the Romans simply couldn’t cope. As a result the Romans gradually lost territory and the associated revenues in a vicious circle.

It is possible to overstate this case, however. For example, the threat from Attila, despite his reputation, never really became something the Romans could not deal with in the long term. It did however prove sufficient to divert the Romans from the task of retaking Africa from the Vandals in 441, and this had a longer term impact.

For an excellent book which comes down firmly in the ‘barbarian invasion’ camp I thoroughly recommend Peter Heather’s “The Fall of the Roman Empire: A New History” (ISBN 0330491369).

One idea that persists is that the Roman army’s use of ‘barbarian’ mercenaries lead to a decline in the effectiveness of the core Roman army and also provided the opportunity for the mercenaries to rebel. However the Romans had used non-Roman forces almost from the start of the republic (just think of the Alae in the Polybian army, and the Auxiliaries in the late Republic / early Imperial era) and there is no reason to suppose they were less able to control such forces in the later Empire. There were also plenty of precedents for groups of refugees being accepted into the Empire.

Internal decay

There are many variations on the theme of internal decay. It is impossible not to mention Edward Gibbon’s famous work “The Decline and Fall of the Roman Empire”. Gibbon’s view was that the Christianisation of the Roman Empire took away their warlike spirit, though there seem to me to be many examples throughout history demonstrating that religion and warfare can thrive together.

Another version of this theory is that the expansion of the central bureaucracy was at the expense of local, civic pride. The evidence often quoted in support of this is that there was a marked decrease in dedications by local ‘nobility’ across the empire. However it is perfectly possible that this was simply due to the reduced need for new building work once a town had acquired the full complement of civic buildings.

A far more powerful case can be made for the view that political instability at the very top was a major factor in the decline of the empire. Adrian Goldsworthy argues this case in his book “The Fall of the West: The Death of the Roman Superpower” (ISBN 0-300-13719-2).

The problems in the 3rd Century AD stemmed from chronic and, at times, almost continuous struggles for the succession to the throne. This was a result of several factors. Firstly, in such a large Empire, it was difficult for any one person to assert their personal authority and influence at all times and in all areas. This meant that it was always possible for a rival in one particular part of the Empire to claim that he would look after the interests of that area better than the existing Emperor. If he could claim the backing of the local army or (more usually) was the commander of that part of the army, he could then assert that claim by force.

Secondly, once the system of succession that worked so successfully in the 2nd Century had broken down, it proved extremely difficult to restore it. This was largely because it could only be established by nominating close relatives, and many of these proved unsuited to the task (just look at Commodus, where the rot first began).

Diocletian recognised these twin difficulties and as a result he established the tetrarchy, or ‘rule of four’. In this system there were two senior rulers (‘Augustus’), one in the east and one in the west, each with a deputy (‘Caesar’) who was in effect the nominated successor to the respective ‘Augustus’. This foreshadowed the split into Eastern and Western empires a century later. The tetrarchy may have been good in theory, but in practice it did not survive after Diocletian’s death. Constantine and others saw to that.

Goldsworthy argues that the endless assassinations, rebellions and usurpations left emperors concerned primarily with their own survival. He identifies this as the root cause of the failure of the empire to deal with the threats that were facing it. Certainly there were times, particularly following the death of a strong emperor or general, that the Romans directed their efforts at each other rather than dealing with the intruders on their territory.

Whilst instability at the top was a problem, it is not possible to conclude that the split into eastern and western Empires contributed directly to the fall of the west. As late as 468 the eastern Empire was devoting significant resources to the assistance of the west.

Economic decline

The economic difficulties that the Empire undoubtedly faced from the 3rd Century onwards are often given as the reason the Empire ultimately fell. There was undoubtedly inflation in this period, best evidenced by Diocletian’s price edicts which were almost certainly widely ignored. Archaeological evidence from Britain also shows a decline in activity in the 4th Century. However it is possible to overstate the significance of this, as at the same time the senatorial classes continued to live well off their estates in Gaul for example.

Ultimately, in the absence of detailed statistics regarding the Roman economy we can only speculate how much this contributed to the cause of the Empire’s fall. Personally I find it hard to see economic problems as the root cause, but much easier to see them as a symptom that things were going wrong.

Conclusion

In summary:

• From 376 onwards, large groupings of ‘barbarians’ existed within the Empire but were not under central control.
  
  
• From the 400s onwards these groups caused significant reductions in tax revenues as the Romans lost control (temporarily or permanently) of territory. These losses seriously impaired the Empire’s ability to raise troops and resources.
  
  
• Internal instability, most notably the Emperor’s personal insecurity, hampered the Empire’s ability to respond to these groups.

The loss of tax revenues and the internal instability meant that the Roman response was never sufficient to reverse the loss of territory. Eventually this vicious circle of decline caused the western Empire to unravel.