Following the work of the great eighteenth-century English historian Edward Gibbon, historians frequently refer to the rulers of the Roman Empire who followed the death of Domitian as the “Five Good Emperors,” those who successfully managed the Empire at its height. For almost a century, emperors appointed their own successors from the most competent members of the younger generation of Roman elites. Not least because none of them (except the last, to disastrous consequences) had surviving direct heirs of their own, each emperor would adopt a younger man as his son, thereby ensuring his succession. Rome prospered during this period under this relatively meritocratic system of political succession. It was under one of these emperors, Trajan, that the empire achieved its greatest territorial expanse.
One of the important aspects of the behavior of the “good emperors” is that they fit the model of a "philosopher-king" first described by Plato centuries earlier. Even though monarchy had been repugnant to earlier Romans, during the period of the Republic, the good emperors tried to live and act according to traditional Roman Romanitas, undertaking actions not only for their own glorification but for the good of the Roman state. The borders were maintained (or, as under Trajan, expanded), public works and infrastructure built, and infighting among elites kept to a minimum.
Trajan’s accomplishments deserve special mention, not only because of his success in expanding the Empire, but in how he governed it. He was a fastidious and straightforward administrator, focusing his considerable energies on the practical business of rule. He personally responded to requests and correspondence, he instituted a program of inexpensive loans to farmers and used the interest to pay for food for poor children, and he worked closely and successfully with the senate to maintain stability and imperial solvency. The fact that personally led the legions on major military campaigns capped his reign in the military glory expected of an emperor following the rule of the Flavians, but he was remembered at least as well for his skill as a leader in peacetime.
The next two emperors, Hadrian and Antoninus Pius, did not win comparable military glory, but they did defend the borders (Hadrian gave up Trajan’s conquests in Mesopotamia to do so, recognizing that they were unsustainable), oversaw major building projects, and maintained Roman stability. Hadrian spent much of his reign touring the Roman provinces, particularly Greece. It was clear by his reign that the emperor’s authority was practically limitless, with both emperors issuing imperial proclamations known as “rescripts” while away from Rome that carried the force of law.
This period of successful rule eventually broke down when the practice of choosing a competent follower ended – the emperor Marcus Aurelius, a brilliant leader and Stoic philosopher (161 – 180 CE) named his arrogant and foolhardy son Commodus (r. 177 – 192 CE) his co-emperor three years before Aurelius’s death. Storm clouds had already been gathering under Aurelius, who found himself obliged to lead military campaigns against incursions of Germanic barbarians in the north despite his own lack of a military background (or, really, temperament). He had, however, been a scrupulously efficient and focused political leader. His decision to make Commodus his heir was due to a simple fact: Aurelius was the first of the Five Good Emperors to have a natural-born son who survived to adulthood. As emperor, Commodus indulged his taste for debauchery and ignored affairs of state, finally being assassinated after twelve years of incompetence.
One last dynasty emerged in the aftermath of Commodus’s death, that of the Severans who ruled from 192 - 235 CE. They faced growing threats on the Roman borders, as Germanic tribes staged repeated (and often at least temporarily successful) incursions to the north and a new Persian dynasty known as the Sassanids pressed against Roman territory to the east. The last Severan emperor, Severus Alexander, died in 235 CE, ushering in a terrible period of military defeat and instability considered in the next chapter.