Edward Gibbon, writing in the 1770s, opened his Decline and Fall of the Roman Empire with one of the most famous sentences in English historical prose: "If a man were called to fix the period in the history of the world during which the condition of the human race was most happy and prosperous, he would, without hesitation, name that which elapsed from the death of Domitian to the accession of Commodus." The period he had in mind is the subject of this chapter: the reigns of Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius — the so-called Five Good Emperors. The phrase itself is older than Gibbon: it comes from Machiavelli, who in the Discourses on Livy (1517) distinguished the Five Good Emperors from the bad ones who preceded and followed them.
The thesis is not new and it is not wrong. The eighty-four years between 96 and 180 were the longest sustained period of internal peace, administrative competence, and territorial expansion in Roman history. They were also — and this matters for the chapter — the period in which the imperial succession was, by exception rather than rule, decided not by accident of birth but by deliberate adoption of the most able available adult. Each of the first four emperors of the period adopted an unrelated adult heir as his successor. The fifth, Marcus Aurelius, abandoned the practice and was succeeded by his biological son Commodus — with results that closed the period.
Nerva and Trajan
Marcus Cocceius Nerva (96–98) was a sixty-five-year-old senator with no military experience, chosen by the Senate to succeed the assassinated Domitian and to provide a transition. His one substantively important act was to adopt as his heir Marcus Ulpius Trajanus, a forty-five-year-old general of Spanish provincial origin, currently in command of the Rhine frontier and therefore in a position to oppose any rival claimant by force. Nerva died of a stroke after sixteen months. Trajan succeeded without contest.
Trajan (98–117) is the only Roman emperor formally voted by the Senate "the Best" (Optimus); the inscription was added to his official titles in 114. He was a soldier-emperor of the older Roman type, more comfortable on campaign than in court. His two major wars were the Dacian Wars (101–106), which conquered the wealthy gold-mining kingdom of Dacia (modern Romania) and added it as a province; and the Parthian War (114–117), which briefly extended the empire to the Persian Gulf, capturing Ctesiphon. The eastern conquests were unsustainable and were abandoned by his successor, but Dacia would remain a province for 165 years and would, by a process the Romans did not anticipate, become a Latin-speaking population whose language has survived to the present day. (Modern Romanian is, of all the Romance languages, the only one descended from the speech of an isolated Latin-speaking population beyond the imperial frontier; the country's name preserves the fact.) Trajan's Column in Rome, completed in 113, records the Dacian campaigns in a continuous spiral relief of 155 scenes; it is the single most detailed surviving record of Roman military practice.
Domestically, Trajan rebuilt the imperial harbour at Portus, built a new forum in Rome larger than all previous fora combined, set up a charitable foundation (the alimenta) that provided grain allowances for poor Italian children, and corresponded extensively with his provincial governor in Bithynia, the lawyer and senator Pliny the Younger. The Pliny–Trajan correspondence (Book X of Pliny's Letters) is the most detailed surviving record of routine imperial administration — and includes the famous exchange about Christians in 112, in which Trajan instructed Pliny not to actively seek them out, not to accept anonymous denunciations, but to punish them if they were credibly reported and refused to recant. Trajan died at Selinus in Cilicia in August 117, returning from the Parthian campaign.
Hadrian
Trajan's adoption of his successor was less clear than Nerva's had been. Publius Aelius Hadrianus — Hadrian — was Trajan's distant kinsman, a forty-one-year-old senator and former governor of Syria; the story circulated that Trajan had not formally adopted him before death and that the adoption document was, in some sense, manufactured by the empress Plotina. Whatever the exact truth, Hadrian took the throne in August 117 and held it for twenty-one years.
Hadrian was, by Roman standards, an unusually intellectual emperor: a Greek-speaking philhellene, an amateur architect, a patron of philosophy, a writer of bad poetry. His reign was marked by an absence of military expansion. He abandoned Trajan's eastern conquests in 117, fixed the empire's frontiers as a deliberate policy, and toured the provinces almost continuously for twelve years, inspecting the army and the civil administration in person — the first emperor to do so on this scale. The major surviving monuments of his reign are the two great frontier works: Hadrian's Wall in northern Britain (begun 122, 117 km long, two-metre wide stone wall with sixteen forts, sixty milecastles, and 158 turrets) and the German Limes (a continuous palisade and ditch from the Rhine to the Danube). They are the most physically visible expression of the Hadrianic policy of consolidation.
In Rome, Hadrian built the new circular temple known as the Pantheon (begun 118, completed c. 126; the unsupported concrete dome of 43.3 m diameter remained the largest in the world until the fifteenth century, and the second-largest until the twentieth); his mausoleum on the Vatican bank of the Tiber (now Castel Sant'Angelo); and the great country villa at Tivoli, with its half-scale reproductions of monuments he had liked on his travels. His one major war — the suppression of the Jewish revolt of Simon bar Kokhba in Judaea, 132–135 — was savagely fought; perhaps half a million Jews were killed, the rebellion's surviving leaders were executed, and the province was renamed Syria Palaestina with the explicit intent of erasing the Jewish association. Hadrian died at Baiae in July 138, aged sixty-two, after a long illness. His adopted heir was the gentle and uncontentious Antoninus Pius.
Antoninus Pius and Marcus Aurelius
Antoninus Pius (138–161) reigned for twenty-three years without leaving Italy, fought no major wars, and made no substantive changes to imperial policy. His reign is the empire at its most stable. The first volume of Decline and Fall has barely twenty pages on it, because so little happened. He is best remembered today through his adopted son and successor.
Marcus Aurelius (161–180) is the most famous of the five emperors because of the Stoic philosophical journal he kept during the last decade of his life — the Meditations, written in Greek for himself and never intended for publication, but preserved by accident and read continuously since the Renaissance. The book is one of the principal surviving documents of Stoic ethics and one of the most-quoted texts in the entire ancient corpus. Marcus also fought, almost continuously after 167, in the long Marcomannic Wars on the Danube frontier — a defensive campaign against Germanic confederations whose pressure on the limes would, in the next century, escalate into the crisis that nearly destroyed the empire. He died on the 17th of March 180, aged fifty-eight, at military headquarters in Vindobona (modern Vienna), probably of plague.
Commodus and the end of the period
Marcus's only surviving son, Lucius Aurelius Commodus, was eighteen at his father's death and had been groomed for the throne for years. He inherited the throne by biological succession — the first time an adult biological son had succeeded a Roman emperor since the reign of Vespasian — and he immediately reversed the policies of his father, making peace with the Germanic tribes on terms his father would not have accepted and returning to Rome to enjoy the spoils.
Commodus's twelve-year reign (180–192) is the standard example, in Roman history, of how the system of biological imperial succession produced incompetent or unstable rulers. He renamed Rome Colonia Commodiana, fought 735 recorded gladiatorial bouts as an amateur (against carefully arranged opponents), declared himself the reincarnation of Hercules, executed senators on increasingly slight pretexts, and was strangled in his bath by his wrestling partner Narcissus on the 31st of December 192, at the instigation of his concubine and his praetorian prefect. He was thirty-one. The Antonine dynasty was over. The system that had produced four consecutive competent emperors by adoption had collapsed within one biological generation. The next century would be considerably less peaceful.
End of Chapter III