If people today know anything about the Roman Empire, it is that it fell. This is without doubt the best-known `fact' about Ancient Rome, just as Julius Caesar is the most famous Roman. Rome's fall is memorable because its empire lasted for so long - more than five hundred years after Caesar's death in Italy and the western provinces, and three times as long in the east, where emperors would rule from Constantinople until the fifteenth century. The Roman Empire was also exceptionally large - no other power has ever controlled all the lands around the Mediterranean - and left traces behind in many countries. Even today its monuments are spectacular - the Colosseum and Pantheon in Rome itself, as well as theatres, aqueducts, villas and roads dotted throughout the provinces. No other state would construct such a massive network of all-weather roads until the nineteenth century, and in many countries such systems would not be built until the twentieth century. The Roman Empire is often seen as very modern and highly sophisticated - glass in windows, central heating, bath houses and the like - especially by visitors to museums and monuments. This makes Rome's fall all the more remarkable, especially since the world that emerged from its ruin appears so primitive by contrast. The Dark Ages remain fixed in the popular mind, even if the term has long since been abandoned by scholars.

Why Rome fell remains one of the great questions of history. In the English-speaking world `fall' is inevitably coupled with `decline', for the title of Edward Gibbon's monumental work has become firmly embedded in the wider consciousness. No other eighteenth-century history book has remained so regularly in print in various forms and editions until the present day. There have been plenty of other books written on the subject, and some have been more perceptive in their analysis, even if none has ever challenged The Decline and Fall of the Roman Empire as one of the great works of English literature. In later life Gibbon liked to believe that it was his destiny to be an historian and to chronicle the great theme of Rome's fall. He claimed a specific moment of inspiration: `It was at Rome, on the fifteenth of October, 1764, as I sat musing amidst the ruins of the Capitol, while the barefooted fryars were singing Vespers in the temple of Jupiter, that the idea of writing the decline and fall of the City first started to my mind."

Gibbon produced several versions of this story, creating the suspicion that he embellished or even invented the memory. On the other hand it is hard for any visitor with imagination not to think similar thoughts, for past and present seem very close beside the centre of Ancient Rome. The `barefooted fryars' are no longer so obvious, and have been replaced by the ubiquitous hawkers, switching instantly from offering sunglasses to umbrellas whenever the weather changes. Even the crowds of other tourists tramping along the Sacra Via help to give a sense of the bustle and noise of the ancient city, once every bit as busy and active as the modern city that now surrounds it.

Rome is not only a museum, but also a vibrant community, the capital of a modern country and the centre of the worldwide Catholic Church. The reminders of ancient grandeur sit side by side with homes, offices and restaurants. Rome was never abandoned, although it shrank massively in population from the height of the empire in the centuries after its fall. A good number of other modern cities are also built on Roman foundations, something still visible in their grid-shaped street plans. Other Roman cities vanished altogether and those in desert areas produce some of the most romantic ruins visible today. When the Roman Empire fell, life did not simply stop in the lands it had controlled. The context of life certainly changed, sometimes dramatically and quickly, but in other cases much more gradually. As the specialists on the period have long since made clear, the Dark Ages were not wholly dark, although by any reasonable standard they were dark enough in comparison with the Roman period. Many things became more local, such as power and trade, and often the world was a more dangerous place, with raiding and warfare between nearby communities now a real possibility. Quite quickly there was no one with the money or skill to build great monuments such as theatres, aqueducts or roads. In time, it even became difficult to maintain the ones that already existed. Scholars are deeply divided about when, how and why the world changed from the Roman era to the basis of the medieval world that took shape in the following centuries. None doubt that the change occurred.

Gibbon admired the achievements of the Roman Empire at its height, as did all educated Europeans in his day. This in no way reduced his enthusiasm for the modern world, and especially for the constitution of his own country, where the monarch's power was limited and guided by the aristocracy. Gibbon knew that his own country and its neighbours across the Channel all owed their origins to the various barbarian groups that had carved up the Roman Empire. Therefore, in time, good had come from chaos and destruction, and from his perspective the world - or at least the Western world - had in the long run developed along the right lines. This mixed attitude to Rome's fall remains a central part of its fascination. It serves as a warning of mortality. The emperors who built the great arches in the Forum all died like any other human being. Eventually their empire - so rich, so powerful, so sophisticated and so utterly self-confident - also came to an end, its monuments crumbling away into ruin.

The imagery of Ancient Rome has frequently been invoked by more recent states for its associations with the ultimate heights both of power and civilisation. It is never long before talk also turns to Rome's fate. Insiders to the modern great power usually see this as a humbling reminder that everything passes, and perhaps as a warning against complacency and corruption. Outsiders, and especially those resentful of the power of others, tend to prefer the thin comfort of the belief that the current power will eventually fall. Many states have been compared to the Roman Empire. A century ago the most natural comparison would have been with Britain, and then perhaps with France or one of the other great empires of the age. Nowadays, it is inevitably with the United States of America.

The form varies, as does the tone. In recent years the best-selling novelist Robert Harris has written about Roman themes, openly declaring that this was a way of commenting on modern America. The B B C also screened a television series hosted by the former Python Terry Jones called Barbarians, with the theme that the reputations of other nations had been blackened by Roman propaganda. It was highly entertaining stuff, even if the message was somewhat strained - the Greeks would certainly have been most surprised to be considered barbarians, since they were the ones who first coined the term for the rest of the world. In interviews at the time, Jones made clear that the series was drawing a direct parallel with the American superpower, and openly criticised the war in Iraq. For many, criticising Rome has become a way of criticising American policy and culture. Inevitably, this affects their view of both.'

Milder and less detailed criticism is even more common. At certain sorts of parties, the discovery that I am an ancient historian almost inevitably prompts someone to remark that `America is the new Rome.' More often than not this is followed by a smug, of course, they don't see it.' This at least is utterly false, for Americans have been comparing their country to Rome since its foundation. In shaping the new country, the Founding Fathers consciously hoped to copy the strengths of the Roman Republic and avoid its eventual downfall. These days, it is also fair to say that the different university systems tend to make educated Americans broader in the range of their knowledge than the British. Plenty of engineers or medical doctors in America will at some point have taken a course or two in history or even the classics, something which is unimaginable on this side of the Atlantic. This is one of the reasons why Roman analogies remain exceptionally common in the USA, and are routinely made by politicians themselves as well as journalists, political commentators and the wider public. Usually it begins with the assumption that the USA as the sole superpower left in the world is dominant in a way unmatched by anyone since the height of Roman power.

In the summer of 2001 I took part in a two-day seminar organised by the Center for Strategic and Budgetary Assessments, which was US government-funded by the Office of Net Assessments. Six historians were brought to a nice hotel in Washington DC - as one of the older and more distinguished members of the group put it, `They obviously don't realise what academics will put up with.' We then gave papers and discussed the grand strategies of various great powers from history. We were just a small part of a wider series of seminars and research sessions aimed at providing insights about future relations between the USA and the emerging power of China. The talks and discussions were enjoyable and fascinating - it is quite rare in academic circles for conferences to cover such a wide range of periods, including First Empire France, Germany in the First and Second World Wars, and British naval policy in the early twentieth century. Yet it was striking that two out of the six of us had been asked to speak about different periods of Roman history.

It is in fact an odd sensation for an historian to talk to an audience that is actually listening to what you are saying. In the university context, most people tend to be thinking more about what they will say in comment on a paper. The subject matter is also literally of no more than `academic' interest, and however excited and enthusiastic we feel about the topic, this is simply because the hope is always to discover the truth. It is rather humbling to think that at many, many removes, and in the tiniest way, someone may try to shape policy on the basis of your analysis. This naturally focuses the mind in a way no purely academic meeting ever does. It becomes even more important to get at the truth of your subject. At the same time the idea that a government agency is genuinely trying to learn lessons from history is hugely encouraging. Again this is something far more likely to happen in the USA than over here in Britain.

Many people feel that they can see clear similarities between Ancient Rome and the modern world. Comments and questions about this have been overwhelmingly the most frequent during interviews publicising my biography of Julius Caesar. This has been true everywhere, but especially in the USA. Yet the conclusions people draw from these perceived parallels vary immensely and, inevitably, have a lot to do with their own political beliefs. It has always been easy to learn lessons from history, but all too often this is simply the case of using the past to justify modern ideas. Any close look at the Roman Empire will soon reveal massive differences with any modern state, including the United States. None of this means that it is impossible to learn from the past, simply that it must be done with considerable care and a good deal of caution.'

This is not a book about modern America and its place in the world, something which others are far better placed to write. It is a book about the collapse of the Roman Empire, which vanished in the west and was eventually left as little more than a rump in the east. The aim is to understand the history on its own terms and in its own context. Historians do not always make the best prophets. The seminar I mentioned earlier was followed just a few months later by the terrorist attacks of 9/11. I would imagine the report produced after the series of conferences is now gathering dust somewhere as immediate priorities have shifted so profoundly. I am pretty sure someone at the seminar made a brief comment about China not posing the only serious threat and about the continued importance of oil and the Persian Gulf, but I may be imagining it. Certainly, none of us gave the impression that we expected that soon America and its allies would be fighting two major conflicts on land. I for one would certainly never have imagined that British Forces would be back in Afghanistan, on the other side of the old North-West Frontier.

This book is about Rome, an empire long vanished and from a world where the technology and culture were so very different from today. Understanding that world is the only way to understand Rome's fall. Filling the pages with constant references to the present day is unlikely to help achieve this. It is more than a little odd to read studies of the Roman period describing the `shock and awe' of the invasion of Britain in 43. It is even stranger when the discussion of the end of a Roman province provides the opportunity for criticism of Bush and Blair and the war in Iraq.4

The Roman Empire did not fall quickly, but as part of a very slow process, and this should warn us against magnifying current events and their likely consequences on the long-term fortune of countries. Britain has been a fairly depressing place in the last decade or so. Ministers caught out in incompetence, corruption or blatant deceitfulness cling on to power like limpets, first denying everything, before finally apologising and expecting this to be enough. Bureaucracy and regulation continue to grow apace, while the basic efficiency of institutions declines, rendering them incapable of even the apparently simple tasks. Yet while the number of civil servants rises, the size of the armed forces shrinks at the very time they are more heavily committed to serious campaigns. It would be easy to draw parallels with the Roman Empire in the fourth century. The self-righteous tone of so much government legislation certainly chimes with Late Roman imperial decrees, as does the apparent failure of so much of this to achieve its aim. Such comparisons are unlikely to assist our analysis of the Roman Empire, and would be no more than the author indulging himself. Understanding the history must come first.

Only at the very end may we reasonably turn to some parallels and even lessons for the present. Some of these will have more to do with human nature than specific policy. I do not claim that any of these ideas are especially profound or original. That does not mean that they are not important and do not apply to any human institution, whether country or company. We should still be thankful that many aspects of the Roman experience are most definitely not mirrored in our own day. Public life is not violent and political rivalries in Western democracies do not explode into civil war.

However, there is perhaps one lesson worth learning from our own times. On an almost nightly basis our television screens carry grim pictures of violence in Iraq and other war zones. Just a few days ago there was the especially sickening incident where initial reports suggested that two young women with Down's Syndrome were employed to carry bombs into a crowd. The explosives were detonated by remote control, murdering their bearers as well as the other victims. Inevitably with attacks where the bombers themselves die it is difficult afterwards to establish the precise facts. However, as usual, these victims were mainly ordinary civilians, not in any way connected with the government or America and its allies. Such dreadful incidents should remind us of the capacity of some human beings to slaughter people who are their neighbours.

Media attention must inevitably focus on such atrocities. They are news, in the way that peaceful daily life is not. What we need to remember is that violence and ordinary life coexist. Frequent targets of suicide bombers or mortar and other attacks are crowded market-places, where people go to buy food and other necessaries. Just a few streets away from an attack, daily routines will be going on much as normal. People go to work and children go to school, people cook and eat, sleep in their beds and do such ordinary things as getting married. Life goes on, because there is really no alternative. Some people will flee, but for many this is not possible. Violence makes all of these things more difficult, and the threat of it spreads fear far beyond the number of direct victims. Yet life will still go on. It is well worth remembering this when we consider the collapse of Roman authority, the end of imperial rule and the barbarian invasions. Perhaps then we will be less impressed when aspects of Roman culture appear to have survived or that occupation by an invader did not result in the flight or extinction of all existing communities.

Looking at the fall of the Roman Empire seemed the logical next project for me after completing the book on Caesar. In some ways it is a departure, for in the past I have mostly studied and written about earlier periods of Roman history. Even after spending the last few years working on this book I still see myself as something of an outsider to the field. I hope that this grants a perspective that is sometimes lost by the period specialist. The work of many others has made it possible for me to write this book. Since it became fashionable a generation or so ago the literature on the later Roman period is now vast and includes some of the most innovative and impressive scholarship seen in any aspect of the study of the ancient world. Newcomers to the field are therefore able to plunder from an array of studies into almost every aspect of the history of these centuries. From the beginning I must acknowledge my debt to these historians and archaeologists, many of whose works are listed in the notes and bibliography. At the same time, the main reason why I wanted to write this book was a dissatisfaction with quite a few of the conclusions and assumptions made in these works. There is no generally accepted explanation for the fall of the Roman Empire in the west in the fifth century. `Fall' is not a fashionable word with a surprising number of the scholars working on the period, and many talk instead of such things as `transformation', accepting that there was change, but casting it in a gentler light. A few voices have been raised against this rosy portrait, but any suggestion of decline still seems tantamount to heresy. The empire of the fourth century in particular is regularly depicted as essentially sound, perhaps even stronger and more efficient than the world of Augustus or Hadrian. I simply do not believe this, and hope to show that it makes no sense whatsoever in the light of the evidence, let alone sheer common sense. In addition, the reasons for the collapse of Roman power deserve an explanation, and oddly the most important factor tends to be dismissed.

An academic study would summarise and list the arguments and analysis of all major contributors to the debate on a subject. Such material is meat and drink to historians and an essential tool of their trade. It is also deathly dull to everyone else. Only rarely will any scholar be mentioned by name in the main text of this book. References to their work may then be found in the endnotes. The overwhelming majority of readers will rightly ignore these, but they are there to help anyone wishing to read more or for those wishing to follow the trail that led me to the conclusions presented here. These and the bibliography are not exhaustive and, somewhat unfairly, usually list only those works in English, since many foreign texts will only be readily available to the few readers with access to a good university library.

In the second century AD the Roman Empire was the overwhelmingly dominant power in the known world. It seems reasonable enough to call it the superpower of its time. The term is meant in only the most general sense. I do not intend to define words like `superpower', `power', or even `empire'. Such rigid labelling is common, but in my opinion rarely instructive. At the seminar mentioned above I remember one scholar for whose work I have immense admiration baldly stating that the British Empire was not really an empire. Doubtless what he meant was that it did not share all of its characteristics with other empires, but it is difficult to see what is gained by such strict definition. No such artificial labelling is necessary to show that by the end of the sixth century the power, prosperity and size of the Roman Empire had been massively reduced.

Similarly I have made no real use of the modern terms `Byzantium' and `Byzantine', and the emperors who ruled from Constantinople are referred to as Roman even when they no longer controlled Italy and Rome itself. This was how they knew themselves. The accuracy of terms like `Germanic' and `tribe' are now hotly debated. I have made use of them because no better alternatives are available. Similarly, the word `barbarian' is sometimes convenient. None of these terms should be interpreted too rigidly.

This book spans more than four centuries and cannot hope to describe the entire history of the period in equal detail. It would easily be possible to expand each of the chapters into a work of similar length to the entire book. Once again, more detailed studies are cited in the endnotes. I have tried to maintain a coherent narrative, although it is sometimes convenient to concentrate on events in one area before dealing with things happening elsewhere. Some issues, such as religion, law and wider society, are dealt with very briefly for reasons of space. This is not because such issues were unimportant, but simply because they were of minor significance for the slow rotting of Roman power. Avery high proportion of our surviving sources are Christian, and it would be very easy for this book to turn into a history of the Church in these centuries. Once again, this would in itself be interesting, but it would be a digression from our real theme. The focus must always be on the factors and events that led to the eventual fall of the empire, and this is the story that this book attempts to tell. It is undoubtedly one of both decline and fall.

Before proceeding it is only right for me to thank the many people who helped me to write this book and listened patiently to my ideas. Some also read various versions of the manuscript and provided very many helpful comments. In particular I would like to thank Geoffrey Greatrex for finding the time amidst his heavy teaching and research load at the University of Ottawa to read all the chapters. Thanks to him I have been pointed to many works that I would not otherwise have found. Both Kevin Powell and Perry Gray were also kind enough to read the text. Each commented in a distinctive way and I can only regret that lack of space made it difficult to include some of their suggestions. Once again Ian Hughes has read and commented on the very first drafts of all the chapters, and has probably been very glad to move into a period more to his taste. Finally, I ought to thank my mother, Averil Goldsworthy, who has proofread almost all of my books in the past and become a little weary of being blanketed with a general thanks to family and friends. All of these have my thanks and have helped to make this a better book than would otherwise have been the case.

I would also like to thank the staff at Orion Publishing, and in particular my editor Keith Lowe, for all their labours in turning a bare text into the finished book. Similar gratitude is owed to Beene Smith and the people at Yale University Press, both for their past work on Caesar and future efforts for this book. Lastly I must thank my agent, Georgina Capel, for once again creating the circumstances in which I could do justice to such a big topic.

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