The work is divided into three parts. Part 1 traces the reign of Marcus Aurelius through the Crisis of the Third century to the rise of Diocletian. In many ways the reign of Marcus Aurelius was the height of the empire left by Augustus, but the generations that followed witnessed a painful transformative process. Part II begins with Diocletian's attempts to rebuild from the rubble, reorganizing the empire into a new entity. It ends with the political split of the empire between East and West. Part III then details the sordid legacy of the Western Empire as emperors fought rivals, and barbarian warlords fought Roman generalissimos who were themselves often of barbarian extraction. The West increasingly loses ground until it is a patchwork of barbarian kingdoms loosely carrying on Roman traditions. Part III ends with the rise of the Islamic invaders who in turn dismember the outer realms of the surviving Eastern empire.
Goldsworthy's book is largely in response to the most recent scholars, such as Peter Heather, who paint a picture of a vibrant later empire only torn apart by Germanic supertribes and a reborn Persian superpower. Goldsworthy disagrees on both fronts. He claims there is no sufficient evidence to paint the later empire as being as prosperous or as strong as Augustus' Principate. Nor does he see the Persians or various barbarian tribes as being especially larger or more organized opponents than what confronted the earlier emperors. Instead Rome's greatest enemy was itself. The constant civil wars fought after Marcus Aurelius destabilized Roman society and weakened the borders, allowing otherwise weak enemies to exploit Roman instability.
The later emperors cared more about mere survival than about imperial welfare at large, which led to deleterious reforms. Senators were excluded from military command so as to no longer threaten the emperor, but ironically this opened the power struggle to a much wider and far less predictable strata of society below them, namely Equestrian officers and bureaucrats. Furthermore, the split between the civil bureaucracy and the military forces, and the increasing division of both into smaller units, was designed to prevent any one official from having the resources to overthrow the emperor. But this also had the effect of reducing the empire's ability to quickly marshal the necessary resources to oppose foreign invasion. The result was of course an increasing trickle of foreign foes who were allowed to occupy the land, thus depriving the West of needed tax revenue, which in turn weakened the army and bureaucracy, and so encouraging more infiltration and forced settlement.
The tale of western Roman collapse is a long and depressing epic, but Goldsworthy tells it expertly. The prose is enchanting: intelligent but direct and always engaging. Where some saw his Caesar biography as rather needlessly verbose, the author manages in this work to condense about four hundred years of Roman history into as many pages. The books also contains various maps and illustrations, charts and tables, and several pages of photographs. The last hundred pages is populated by a chronology, glossary, bibliography, end notes and an index. This is an excellent narrative for the general reader interested in late antiquity, whether or not one fully agrees with the author's conclusions.