In about 2500BC, Britain was invaded by the “Beaker People”. This was a mass migration from continental Europe, which left its clear traces in the distinctive style of pottery beakers used by the newcomers (hence their modern name). In a prehistoric version of ethnic cleansing, the old Neolithic population were driven out. In came a new social order, new techniques of craft and agriculture, and possibly the first alcoholic drink to be consumed in these islands.

At least, that is what we used to be taught. There were always problems with the story as an explanation of cultural change. Why, for example, was it assumed that new styles of pottery necessarily ­indicated an influx of foreigners? After all, the passion for chinoiserie in the 18th century had nothing to do with an influx of Chinese.

But the idea of prehistoric mass migration seemed to be supported by what was observed in a much better documented period of European history. For during the first millennium AD, the face of Europe was changed by a series of invasions or migrations (it’s sometimes hard to tell the difference). As Peter Heather rightly emphasises in Empires and Barbarians, the old Roman empire had been focused on the Mediterranean, with a northern hinterland. By AD1000, that hinterland had become the centre of the new European world — as it remains today.

Responsible for this massive change in geopolitics were various “peoples”, who moved into, or across, Roman territory: Huns, Goths, Saxons, Vikings, Magyars and hosts more. Late-Roman writers have even left us memorable accounts of these hordes on the move. Ammianus Marcellinus, for example, in the 4th century AD, described huge numbers of Goths moving towards the banks of the river Danube and the borders of the Roman empire; they had been driven out of their own homelands, he claimed, by another mass migration — of Huns.

But that too is what we used to be taught. For recently — following archeologists who had come to prefer the “chinoiserie” to the “Beaker” model of cultural change — many historians have challenged any notion that the changing geopolitics of early medieval Europe could be explained by mass movements of “peoples”. For a start, so this new orthodoxy has it, the idea of peoples with a clear identity drastically misrepresents what were in reality fluid and unstable sociopolitical groups. And, if there was some movement, it must have been on a much smaller scale and less systematic than the old model of migration implied.

What about the written evidence of historians such as Ammianus? Quite simply, they were wrong. The Romans had a dread fantasy about organised and mobile groups of barbarians (one that we have inherited). But they could not have had much reliable information about the societies beyond their borders, let alone who was a Hun and who was a Goth.

Heather has a fine track record in rescuing historical babies from being thrown out with the revisionist bathwater. His The Fall of the Roman Empire put a new case for the old view that barbarian invasions were an important factor in the collapse of the Roman empire. Empires and Barbarians partly overlaps with that, reinstating mass migration as an important phenomenon in the first millennium and one key factor in the formation of modern Europe.

This is not merely an attempt to turn back the ­historiographical clock. Heather has no patience with the old “billiard ball” model of migration — in which, as Ammianus saw it, Huns bumped into Goths and so pushed them towards the Roman empire. Instead he has tried to look at the first millennium afresh, using modern theories of migration and its motives. We are not dealing with anything like the vast Rwandan exodus, but many of the claimed movements would fit the patterns observed in recent history: people tend to move from poorer to richer regions; groups with a tradition of migration tend to be more mobile than those without; people tend to migrate to areas about which they have information. All those conditions apply to Ammianus’s Goths moving towards the Danube.

In theory, his argument works well. But, as Heather admits, beyond the theory it is often hard to find conclusive evidence for any of these migrations. Take the wars of Marcus Aurelius in the AD170s against the Marcomanni tribe on the Danube, commemorated on his great column in the centre of Rome (twin of the Column of Trajan). Heather suspects this war was more than “a normal frontier tiff”, but driven by deeper currents of migration. However, the only ancient hint of that comes from a late-Roman historian, who is flagrantly unreliable even by the standards of his time. Archeology, it is true, has revealed changing patterns in barbarian burials and artefacts in the region during roughly the same period — though whether this was caused by population change or not (the “Beaker/chinoiserie” problem) is uncertain. Even if it were, the dating is so vague that we could not tell whether it was a cause or effect of the Marcomannic war.

At one point, in desperation, Heather has to appeal to Aurelius’s column. Surely he would not have put up such a vast monument to celebrate victory in a “frontier tiff”. He would have been a laughing stock. The truth is that Roman emperors were capable of vastly disproportionate celebration of tiny victories. Impressive as it is, the column is very ­fragile evidence indeed for mass German migration.

Empires and Barbarians by Peter Heather
Macmillan £25 pp734

Times Recommends

• Superfreakonomics by Steven D Levitt and Stephen J Dubner
• The Times picks the 50 best paperbacks of 2009
• Vincent van Gogh’s letters show the soul of the artist