The end of imperial Rome is no great mystery. The empire was brilliant, proud and cultivated, an elaborately complicated society capable of great cruelty, great beauty, and technical genius of every sort: a society in which we see our own far-away mirror. But it grew rich, fat, decadent, lazy and too big to defend. After slow centuries of decline, in the 5th century the defences crumbled and the barbarian hordes – the opposite of everything the Romans stood for, their dreadful Other – poured in.
Why it happened is a matter of endless scholarly debate. Edward Gibbon started it, and while still revered for the scale of his research (and by many for his diagnosis), dozens of others have added their own interpretations.
But now a vast new exhibition in Venice's most important museum, Palazzo Grassi, at the opposite end of Piazza San Marco from the Duomo, asks us to look at the cataclysmic end through a new pair of spectacles.
Rome collapsed, the barbarians poured in, and the Dark Ages got under way: that's the "1066 and All That-style" breakdown.
But what if the barbarians weren't all that barbaric after all? What if the black/white, good/bad, God's chosen versus axis of evil, neo-conservative type explanation for this historical event is just as much state propaganda as the claim that Saddam Hussein was an hour away from bombarding us all with nuclear missiles?
The new exhibition asks us to consider this revolutionary hypothesis, but it has not been plucked out of thin air. With the exception of the genuinely terrifying Hun, who came roaring across the steppe on their ponies and sacked the city of Aquileia in 452, all the other barbarians beating at the door of Rome had been around for a long time: the Visigoths and Lombards in northern Italy, the Ostrogoths in Spain, the Franks in what is now France and Germany.
Their intercourse with the mighty empire had continued for centuries, war and peace alternating, barbarians brought into the Roman armies, tempted within the pale of empire. In fact, one of the most persuasive explanations for the final collapse was that the Romans had grown too dependent for their imperial defence on treaties with these fickle outsiders.
But what the new exhibition lays finally to rest is the notion that the barbarians were barbaric. True, they were often blond, worshipped their own gods, lacked cities with sewerage systems, heated floors, bathhouses and aqueducts. Often they were nomads. But the idea that they were in some absolute sense less civilised was Roman state propaganda. Crueller than the Romans? Hardly possible. More violent, more militaristic than the most militaristic state in history? Hard to conceive.
Once one steps back from the paranoid them-and-us, self-and-other way of looking at it, one sees that rather than the cataclysmic end of a great civilisation and its replacement by the forces of darkness, something far more compelling and creative was under way: the creation (as the curators of this exhibition put it) of Europe as we know it, welded together by Christianity, and with deeply rooted memories of Roman heritage which make dramatic returns to our collective consciousness every few hundred years: during the Renaissance, for example.
"The Barbarian kingdoms," writes Jean-Jacques Aillagon in the catalogue, "gradually drew a new political map of Europe, dividing it between the Ostrogoths and the Lombards in Italy, the Franks in western Germany, Belgium and France, the Visigoths in Languedoc, Aquitaine and the Iberian peninsula."
He continues: "If Europe was born in Athens, Jerusalem and Rome, many of its roots also lie in the peoples of the north and east of the European continent." The aim of the exhibition, he writes: "Is to reveal the profound and subtle mix between Graeco-Roman and Germanic roots from which European culture stems."
Rome was first sacked by the Visigoths in September AD410. The rulers of the empire had seen the disaster approaching for decades and the capital had been moved to the more easily defended city of Ravenna years before. But the extent of the trauma is hard to exaggerate: the last time Rome had been treated this way was a full 800 years before, when besieged by the Gauls in 390 BC. Supremacy had long been a Roman habit.
The reason we have such difficulty grasping what happened to the Roman Empire in terms of continuity rather than disaster was because the Roman propagandists were very good. The word barbarian came from Greek, and Herodotus spelt out what was wrong with them. "Barbarians can neither think nor act rationally... barbarians are driven by evil spirits... which force them to commit terrible acts... Their lust for gold is immense, their love of drink boundless... They are given to gross personal hygiene [and] run dirty and barefoot... Their reproductive energy is inexhaustible."
And of course that's why they had such big families. And they all wanted to move in. And more and more did so, as demographic disaster within the empire made it ever harder to defend itself from its own resources. Some of them even became emperors, like Magnentius, who lived from AD303 to 353, who usurped the rule of Emperor Constantius but took his life three years later after the Eastern Empire in Constantinople refused to recognise him.
The greatness of Rome involved the ritual defeat, humiliation and enslavement of barbarians. Great works like the Portonaccio sarcophagus, among the 1,700 exhibits in this huge exhibition, shows in gory detail a battle between the two sides from which the Romans would emerge inevitably triumphant. Trajan's column and the triumphal arches of Rome are emblazoned with these victories.
Having defined their world, for the empire's greater glory in such stark terms, an eventual reversal was inevitable. The arrival of the Visigoths at the gates of Rome in AD410 was the beginning of a mighty nemesis for which Romans had prepared for centuries. But all the time they were parading their triumphs and dreading defeat, a quite different process was under way: Roman and barbarian culture were quietly inter-breeding. And finally, as the exhibition organisers spell it out, "together they gave birth to medieval Europe".
Rome and the Barbarians: Birth of a New World, is showing at Palazzo Grassi until 20 July
A West Germanic tribe originally living north and east of the lower Rhine, under the Merovingian dynasty, they founded one of several German monarchies that replaced the rule of the western Roman Empire after the fall of Rome. One group of Franks, the Salians, formed a kingdom on Roman soil recognised by the Romans. In the sixth century, after the collapse of Roman authority, the Franks were united under the Merovingians and ruled almost the whole of what is now France. The Salians were important in helping spread Christianity across Europe.
The Visigoths, the first barbarians to successfully attack Rome in 800 years, are one of two main branches of the eastern German Goth tribes. They were first heard of in Poland in 100BC, then migrated slowly south through Slovakia, stopping at the border of the Roman Empire on the north shore of the Danube, where they asked permission from the Romans to stay. They adopted a sedentary lifestyle, farming and trading with the Romans until they began to be forced southwards by the Huns in about AD300. They won a war against the Romans in AD378 and later became a dominant power in the Iberian peninsula.
The Germanic tribes from northern Europe came into collision with the Romans from the 2nd century BC, when they were reported to be moving into Gaul, Italy and the Iberian peninsula, provoking Julius Caesar to annex Gaul and warn of a growing threat of "Germania Magna" which Rome would have to meet. But the occasional wars with Rome were mixed with trade, military alliances and cultural exchanges typical of the complex Rome-barbarian relationship which the exhibition in Venice documents. The collapse of Roman power in the fifth century meant an intensifying period of migration for the tribes – but also in the longer run a regression to an Iron Age level of culture.
Possibly of Turkic origin, the dreaded Huns first appeared in Europe in the fourth century, having emerged from central Asia. They were first identified near the Black Sea, forcing a large number of Goths to seek refuge within the Roman Empire. The Romans rashly invited them inside their Empire in AD360. Under Attila they set up the Hunnish Empire in the fifth century, stretching from the steppes of central Asia to Germany and from the Black Sea to the Baltic, with an efficient system of taxation, augmented by the plundering of Roman cities in Italy. The Empire dissolved after Attila's death in AD453.
Originally Germanic tribes living in eastern Germany, they invaded parts of what are now Romania and Hungary in AD270, forcing Emperor Constantine to make a treaty with them and give them land. Subsequently they moved to Spain then crossed into northern Africa, captured the Roman city of Carthage and made it their capital. They built up a strong army and navy and in AD455, under their leader Genseric, landed at Ostia, the port of Rome, and sacked and plundered the city for 14 days, the second such event after the attack by the Visigoths in AD410.Thousands of Romans were slaughtered and the Empress and her two daughters taken hostage.
The other great Gothic tribe along with the Visigoths, they migrated into Roman lands in the Balkans, driven by the Huns. The greatest Ostrogoth leader was Theodoric the Great, born around AD454, a refined and highly educated man, brought up as a diplomatic hostage in Constantinople. He took Ravenna in AD496, set up his capital there and attempted to revive the arts and sciences of the Romans. He was also an important force in the spreading of the influence of the Catholic Church, and oversaw the short-lived reunification of the Ostrogoths with their cousins the Visigoths.