The Five Good Emperors: The High Point of Rome

In the year 96 CE the Roman Senate made a decision that would determine the next eighty-four years of imperial history. After the assassination of the tyrant Domitian, the Senate did what it had not done in nearly a century: it chose the next emperor itself, picking an elderly, childless senator named Nerva. Nerva in turn adopted a brilliant general from Spain named Trajan as his heir, and the pattern was set. For nearly a century, each emperor would select his successor not from among his biological children but from among the ablest men in the empire, adopting him and training him for the purple. Together with Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius are known to history as the Five Good Emperors, the period in which the Roman Empire reached the peak of its power, prosperity, and territorial extent. For a broader survey of all the emperors, see Roman Emperors.

The phrase “Five Good Emperors” itself is a later invention, but it is one that has stuck. Edward Gibbon, in his Decline and Fall of the Roman Empire, called the period between Nerva and Marcus Aurelius “the period in the history of the world during which the condition of the human race was most happy and prosperous.” The label is generous — Trajan’s wars were devastating, Hadrian was cold, and Marcus Aurelius spent his reign on the Danube in a desperate struggle against barbarian invasions — but the era does mark a sustained peak that the empire would never reach again.

Nerva: The Transition (96 – 98 CE)

Nerva (Marcus Cocceius Nerva, 30 – 98 CE) was sixty-six when he became emperor, and he had never held a military command. He was chosen precisely because he was not a soldier and not a threat to anyone. His only act of lasting importance was the adoption of Trajan in October 97 CE as his son, his heir, and his fellow ruler. The gesture was, in effect, a recognition that the empire needed a soldier on the throne.

Nerva’s brief reign was marked by a serious crisis in the Praetorian Guard, which had been Domitian’s instrument and which resented the new regime. In 97 CE the praetorians broke into the palace, forced Nerva to surrender the assassins of Domitian, and openly humiliated the emperor. Nerva’s response was decisive: he went to the Praetorian camp, presented Trajan to the troops, and told them plainly that the adoption was final. The praetorians cheered. Nerva died a few months later, in January 98 CE, of natural causes — the only emperor since Augustus to do so.

Trajan: The Conqueror (98 – 117 CE)

Trajan (Marcus Ulpius Traianus, 53 – 117 CE) was the first Roman emperor from the provinces, born in the city of Italica in the Spanish province of Hispania. He was a career soldier, having served in Syria, Germany, and the Danube frontier. He came to the throne as a fifty-year-old veteran with a reputation for discipline, energy, and accessibility — a man who, according to his contemporaries, would walk through the streets of Rome in the company of his friends with no imperial guard.

Trajan’s reign is best remembered for two great wars of conquest. The first, the Dacian Wars of 101 – 106 CE, was fought against the kingdom of Decebalus beyond the lower Danube. Trajan reduced Dacia to a Roman province, stripped it of its gold and silver mines, and brought back to Rome enough treasure to fund his building program. The spoils paid for Trajan’s Forum, Trajan’s Column, Trajan’s Markets, and a magnificent new public bath complex. The column, 30 meters tall, still stands in Rome, with a continuous relief telling the story of the Dacian Wars.

The second war, the Parthian War of 114 – 117 CE, was more ambitious and less successful. Trajan invaded the Parthian Empire, captured the Mesopotamian capital of Ctesiphon, marched down the Tigris and Euphrates to the Persian Gulf, and even imagined for a moment that he could march on India as Alexander had done. The conquest proved impossible to hold. A great revolt erupted in Judaea and across the Jewish diaspora, and the Kitos War of 115 – 117 CE devastated the eastern provinces. Trajan died at Selinus in Cilicia in August 117 CE, returning from the east, leaving his successor an overextended empire.

The only recorded letter of Pliny the Younger, who served as governor of Bithynia-Pontus, comes from this period. Pliny wrote to Trajan asking how to deal with Christians, and the emperor’s reply established the policy of toleration with administrative caution that would govern Roman religious policy until the time of Decius.

Hadrian: The Consolidator (117 – 138 CE)

Hadrian (Publius Aelius Hadrianus, 76 – 138 CE) was Trajan’s cousin and adopted heir, a cultured and restless emperor who, more than any of his predecessors, defined the visual and architectural character of the empire. He abandoned Trajan’s conquests in Mesopotamia, recognizing that Rome was overextended, and devoted his reign to consolidating the frontiers and traveling almost continuously through the provinces. He spent more than half of his twenty-one years on the road, and almost every province in the empire can claim at least one building built by him.

Hadrian’s most famous frontier monument is Hadrian’s Wall in northern Britain, a seventy-three-mile fortification stretching from the Solway Firth to the Tyne. He had visited Roman Britain in 122 CE and ordered the wall built to mark the northern limit of the province. He also visited the Greek-speaking east, and the city of Athens was his favorite. He completed the Temple of Olympian Zeus, the largest temple in Greece, and he built the massive Arch of Hadrian that still stands in the city.

In Rome, Hadrian is remembered above all for the Pantheon, the most perfectly preserved building of the ancient world. The Pantheon was a complete rebuilding of an earlier temple, finished in 125 CE under Hadrian’s reign. Its dome, 43 meters in diameter, is still the largest unreinforced concrete dome in the world. For the engineering of the dome, see What Was Roman Concrete?. Hadrian was also responsible for Hadrian’s Mausoleum, the great circular tomb on the right bank of the Tiber, which became the Castel Sant’Angelo of the medieval city.

Hadrian’s private life was unhappy. His wife Vibia Sabina was openly cool to him, and his youthful lover Antinous drowned in the Nile in 130 CE during the imperial tour of Egypt. Hadrian’s grief was extravagant: he deified Antinous, founded the city of Antinoöpolis in his memory, and filled the empire with statues of the dead youth. The so-called Antinous of the Vatican is one of the great works of Roman sculpture.

Hadrian’s reign ended in violence. He had adopted a child, Aelius Caesar, who died in 138 CE. He then adopted Antoninus Pius, with the understanding that Antoninus in turn would adopt the young Marcus Aurelius and Lucius Verus. He died at Baiae in July 138 CE, having, as he put it, wished for many things but deserved very few.

Antoninus Pius: The Peaceful (138 – 161 CE)

Antoninus Pius (Titus Aurelius Fulvius Boionius Arrius Antoninus, 86 – 161 CE) was the least eventful of the Five Good Emperors, and that is the secret of his success. He ruled for twenty-three years without major wars, without serious revolts, and without the kind of personal scandal that had marked the reigns of Nero and Domitian. His nickname Pius — “dutiful” — was earned by his devotion to Hadrian’s memory.

The only significant military event of his reign was in Britain. In 142 CE, on the advice of his general Lollius Urbicus, Antoninus pushed the frontier north of Hadrian’s Wall into the Scottish lowlands, building a new turf wall — the Antonine Wall — across the central belt. The new wall was held for only about twenty years before the Romans withdrew back to Hadrian’s Wall.

The most important institution of Antoninus’s reign was probably the development of a professional imperial civil service, the staff of equestrians and freedmen who actually ran the day-to-day government of the empire. The emperor of the second century spent much of his time on the frontiers and in the provinces, and he could not have ruled without the men who stayed in Rome and ran the paperwork.

Marcus Aurelius: The Philosopher-Emperor (161 – 180 CE)

Marcus Aurelius (Marcus Aurelius Antoninus, 121 – 180 CE) is the most famous of the Five Good Emperors, and the only one whose writings are still widely read. His Meditations, written in Greek during the Marcomannic Wars, is one of the great works of Stoic philosophy and one of the most extraordinary documents ever written by a ruler at war. He wrote them for himself, never intending them to be published, and they read like the private notebook of a man trying to live up to the standards of virtue he set for himself.

Marcus was adopted by Antoninus Pius and trained for the purple from infancy. He became co-emperor in 161 CE with his adoptive brother Lucius Verus, the first time Rome had two joint emperors, and he ruled alone after Verus’s death in 169 CE. The first years of his reign were catastrophic. The Antonine Plague, probably smallpox, swept through the empire in 165 – 180 CE, killing an estimated five to ten million people, devastating the army, and emptying the treasury. The Parthian War of 161 – 166 CE cost more than it gained, and the troops returning from the east brought the plague with them.

For the last decade of his reign, Marcus was on the Danube, fighting the Marcomannic Wars against a coalition of Germanic peoples that included the Marcomanni, the Quadi, the Sarmatians, and others. The wars were long, exhausting, and only partially successful. The empire held its frontiers, but at a cost that revealed the limits of its military manpower. Marcus is said to have wept during the campaign, not for himself but for the empire.

The Meditations were written on this front. They are a manual of self-discipline, a sustained argument that the only thing in our control is our own mind, and that the proper response to pain, loss, and death is acceptance. “Begin the morning by saying to thyself,” he wrote in the second book, “I shall meet with the busybody, the ungrateful, arrogant, deceitful, envious, unsocial. All these things happen to them by reason of their ignorance of what is good and evil. But I who have seen the nature of the good, that it is beautiful, and of the bad, that it is ugly, can neither be injured by any of them, for no one can fix on me what is ugly, nor can I be angry with my kinsman or hate him.”

Marcus died at Vindobona (modern Vienna) in March 180 CE, probably of the plague. He was succeeded not by his chosen heir, his adoptive brother’s son Commodus, but by his biological son of the same name, the only biological succession of the adoptive emperors and the beginning of a new crisis. His column, the Column of Marcus Aurelius, still stands in the Piazza Colonna in Rome, and his equestrian statue of the gilded bronze is the only surviving Roman equestrian monument in the world.

The Adoptive System

The succession from Nerva to Marcus Aurelius is one of the most remarkable political experiments in ancient history. There was no law of adoption; there was no written constitution. The system worked because of a small, self-conscious group of Roman aristocrats who agreed, however grudgingly, that the good of the empire required them to pass over their own children for the sake of abler men. Trajan was a Spaniard. Hadrian’s chosen heir Antoninus was from southern Gaul. Marcus Aurelius was of mixed Spanish and Roman descent. None of them had any claim to the throne by blood.

The adoptive system failed with Marcus Aurelius. He had a biological son, Commodus, and a powerful Roman tradition of inherited property worked against his adopting an heir. Commodus, who came to the throne in 180 CE and was murdered in 192 CE, was, by universal consent, a disaster. The empire of the second century was the high point of the Roman state, and the adoptive succession was the political innovation that made it possible. After Commodus, the empire would not see another such system until the Tetrarchy of Diocletian in 284 CE.