A thorough, educational and thought-provoking — if massive and occasionally overwhelming work about the "barbarian invasions" that wracked Europe for more than a half century, coinciding with the fall of Roman hegemony in the West, the rise of successor kingdoms, and then those kingdoms' own struggles against future waves of barbarian invaders. Heather's book is one part history and one part disputation, weighing with voluminous evidence into an academic debate that has fiercely divided the field of Late Antique and Early Medieval studies: is the standard story of barbarian invasions causing the fall of Rome actually true at all?

The revisionist theory holds that the conventional tale of hordes of barbarians moving, families in tow, across vast expanses of Eurasia and leaving the Roman Empire shattered in its wake has little basis in reality. Populations remained relatively constant, with only small numbers of new people moving, and changes in material culture observed in archaeology reflecting cultural change rather than the replacement of one people by another. This argument has the virtue of having been true in at least some times and places, the best-documented of which is the Norman invasion of England in 1066: William the Conquerer's army was relatively small, and simply replaced the old Anglo-Saxon aristocracy with new Norman aristocracy. Life then continued as normal, with a French-speaking elite and Anglo-Saxon-speaking peasantry gradually, over the centuries, developing a common culture.

Heather's book, in documenting the history of the so-called "barbarian invasions," is responding to this thesis, which he says has attained the status of orthodoxy in some parts of the field. He readily acknowledges some of the revisionist points, and critiques the traditionalist view of "nations on the march" for going too far and being too subjugated to 19th Century political concerns. But Heather is convinced that barbarian migration actually does and did happen, and draws on a wide array of historical accounts, archaeological evidence, studies of modern migrations and more to try to convince you, the reader, too.

At the root of Heather's case are arguments based on agricultural economics: complex societies with division of labor and a dedicated warrior caste require an agricultural surplus to support non-farming citizens. In one fascinating aside, he notes that the Germania area that Rome's borders never subsumed had notoriously thick and unproductive soil in antiquity, making it incapable of supporting a large society. Rome never conquered Germania not because it didn't want to, but because by the standards that mattered, Germania couldn't produce enough to justify conquering it. This drawback was only gradually solved as agricultural technology advanced (in particular better plows that could turn the soil), which enabled the area to support larger populations — to the detriment of the Roman frontier.

Using both contemporary observations and archaeological finds (midden-heaps and graves from certain places and times are laden with ornate luxury goods and tools, while others are spare), Heather meticulous documents where we can conclude that migrations happened, where the evidence is sketchier, and where we can be pretty sure that a supposed "invasion" was only a relatively small number of people. This being ancient history, he's forced to fall back on the old "we must suppose" standby more often than a history fan might like, but there's really no way around it and Heather never oversells his evidence. You'll come away better informed about both the facts and the historiographic arguments concerning the surprisingly relevant question of Rome's fall (if you can soldier through more than 600 occasionally dense pages). ( )