Why Rome Fell

2 Diocletian Hammer of the Aristocracy

The Emperor Septimius Severus (r. 193–211) is famously said to have advised his two sons, Caracalla and Geta, shortly before his death: “Be harmonious (between yourselves), enrich the soldiers, scorn all others.” (Cassius Dio, 77.15). Caracalla soon got rid of his brother and behaved arrogantly toward most other people though, in 212, by the Constitutio Antoniniana, he extended Roman citizenship to all free male inhabitants of the empire. As his father had advised, his main concern was the army though his extension of citizenship actually had a detrimental effect on military recruitment. The army was made up of legions, recruited from Roman citizens, and auxilia, drawn from peregrini, non-citizen provincials, who became citizens automatically after twenty-five years’ service. After 212, however, there was no longer any incentive for peregrini to enlist, and more “barbarians” were recruited than ever before.

Between Caracalla’s assassination in 217 and the accession of Diocletian in 284, a succession of emperors met a similar fate. The period from 235 to 284 is known as the Crisis of the Third Century when the Roman Empire’s very existence was threatened by a combination of threats, foreign, domestic, military, political, and economic.

Diocletian’s solution stabilized the Empire, at least temporarily. As a military man, his focus was primarily on defense and security. By sharing his power with three other emperors in the so-called tetrarchy ...