Who were the best and worst Roman emperors in history?
Rome has a long and fascinating history. The Roman Empire would more accurately be described as the Principate (from 27 BCE to 284 CE) and the Dominate (from Diocletian's Tetrarchy). There were 71 emperors and co-regents from Augustus to Theodosius, who definitively split the empire in eastern and western halves in 395. Here is a list of the main emperors rated in categories from best to worst in terms of policy, diplomatic, administrative and military skills, ability to keep peace, achievements and long-term impact. The order within each category is purely chronological.
The best and greatest emperors (augusti optimi maximi)
Augustus (r. 31 BCE-14 CE): The founder of the empire, he ushered in an new era of peace (Pax Romana), which lasted two centuries until the reign of Marcus Aurelius. A talented politician and gifted administrator, he strengthen the economy and built many great monuments. He decentralised power and made the empire a truly cosmopolitan place with an international ruling class. He created Rome's first police force as well as the Praetorian Guard. Marcus Agrippa, his best friend, right-arm and co-ruler for 19 years could be regarded as his co-emperor. If so, he would certainly rank among the five best Roman emperors too.
Vespasian (r. 69-79 CE): He was a soldier-statesman who brought back stability after the turmoils following Nero's suicide and avoided the collapse of the empire. He had good relations with the Senate and granted the rank of senator to many legionary commanders from the provinces. His most visible achievement today is the Colosseum (which was completed by his son Titus). Vespasian also gave financial rewards to writers, including Josephus (his former slave turned friend and advisor), Pliny the Elder (a close friend) and Tacitus (who started his carreer under Vespasian).
Trajan (r. 98-117 CE): Hailed as one of the greatest emperors, Trajan was an outstanding general, a gifted administrator and diplomat and a philanthropic ruler. He conquered Dacia and brought back the largest treasure of the Antiquity, which allowed him to build a new forum and market and the largest Thermae Rome had ever seen. Trajan's personality and accomplishments were seen by contemporary writers as unanimously positive. He was described as wise, just, moral, dignified and fair and was generally beloved by the people and respected by the Senate. At the inauguration of later Roman Emperors, the Senate would say the phrase Felicior Augusto, melior Traiano ("be more fortunate than Augustus and better than Trajan").
Antoninus Pius (r. 138-161 CE): A thrifty and considerate emperor who did all he could to improve the life of common people. His reign was the most peaceful of any emperor. Marcus Aurelius praised Antoninus in the Meditations, calling him a man who was devoted to the empire’s needs, energetic and hardworking, rational and reliable, modest, indifferent to honours and immune to flattery, tolerant and compassionate, and orderly but decisive. Antonius was a skilled administrator and builder. He constructed new aqueducts, roads and bridges, suspended the collection of taxes from cities affected by natural disasters, and still managed to leave behind a sizable public treasury upon his death. He introduced into Roman law many important new principles based on humanity and equality, such as the presumption of innocence and measures to facilitate the enfranchisement of slaves. He punished the killing of a slave by his/her master without previous trial and determined that slaves could be forcibly sold to another master by a proconsul in cases of consistent mistreatment.
The very good emperors
Hadrian (r. 117-138 CE): The third of the so-called "Five Good Emperors", Hadrian has been described as an enlightened autocrat. Despite his arrogance and aloofness, he was politically moderate, equitable and versatile. A great lover of Greek culture, Hadrian was also an architect and sculptor and had dozens of temples built, as well as a sumptuous palace (known as Hadrian's Villa) in modern Tivoli, just outside of Rome. Hadrian's main military policy was to put a halt to Trajan's expansionism and consolidate the borders of the empire, notably with the famous wall he built in northern England. Hadrian travelled more extensively all over the empire than any other emperor and opened new doors to provincial elites.
Marcus Aurelius (r. 161-180 CE): A Stoic philosopher, Marcus was thoughtful, careful, open-minded, reasonable and dutiful. Although he disliked war, he successfully repelled all the barbarian invasions under his reign. He took his responsibilities seriously as an emperor and showed a great deal of respect toward the Senate, routinely asking its permission to spend money even though he did not need to so. He was a proficient administrator and took great care in improving the legislation. He showed marked interest in the manumission of slaves, the guardianship of orphans and minors, and the choice of city councillors. His main failing was to choose his incompetent son Commodus as co-emperor and successor.
Julian (r. as Caesar 355-360, as co-Augustus 360-361, as sole emperor 361-363 CE): Julian was an intellectual, a Neoplatonist philosopher and was also intensely interested in literature and the visual arts. He was also an accomplished general who earned the admiration and respect of his soldiers and of the population. Julian managed to crush an army of Alamanni three times larger than his own in 357. He also defeated the Franks and allowed them to settle in Germania inferior as foederati (they would later became the Merovingians). Although he was a convinced pagan himself, upon becoming emperor he refrained from persecuting Christians in retaliation and restored the religious tolerance throughout the empire, even attempting to rebuild the Jewish Temple of Jerusalem. He tried to salvage Roman culture and paganism from the persecutions started by his cousin Constantine. His reign as sole emperor only lasted 18 months but was seen as a brief Renaissance in the decline of the Roman Empire. Julian purged the top-heavy and corrupted state bureaucracy, dismissing thousands of eunuchs and superfluous officials. He did not seek to rule as an absolute autocrat like earlier emperors since Diocletian. His own philosophic notions led him to idealise the reigns of Hadrian and Marcus Aurelius. He described the ideal ruler as being essentially primus inter pares ("first among equals"), operating under the same laws as his subjects, as opposed to the royal court established by Constantine. As such, Julian was frequently active in the Senate, participating in debates and making speeches, placing himself at the level of the other members of the Senate. He also sought to reduce direct imperial involvement in urban affairs. Despite his early death from a wound while fighting the Persians, Julian stands out among Roman emperors through his erudition, tolerance, probity, dedication and idealism. Julian was lauded by Enlightenement philosophers such as Locke, Montesquieu and Voltaire, who saw him as the ideal sovereign and the mascot of the age of reason. Montesquieu wrote of him: "There has not been a prince since his reign more worthy to govern mankind".
The good emperors
Claudius (r. 41-54 CE): Born with a limp, slight deafness and what may have been cerebral palsy, Claudius was ostracised by his family and never intended to be emperor. As one of the last survivors of the Julio-Claudian dynasty after the internecine struggles and murder spree, he declared emperor by the Praetorian Guard after Caligula's assassination. Despite his lack of experience, Claudius proved to be an able and efficient administrator. He was also an ambitious builder, constructing many new roads, aqueducts, and canals across the Empire. During his reign the Empire began the conquest of Britain. Scholarly opinions of Claudius vary a lot, sometimes depicting him as an intelligent, scholarly, well-read, and conscientious administrator with an eye to detail and justice, or conversely as paranoid and apathetic, dull and easily confused, bloodthirsty and cruel, overly fond of gladiatorial combat and executions, and very quick to anger. The empire generally flourished economically and culturally under his reign, but the same was true also of Tiberius, Caligula and Nero despite their personal deficiencies.
Titus (r. 79-81 CE): The son of Vespasian, he followed in his father's footsteps. He was loved by the Senate, the Army and the Roman people, who praised him for his great virtues. He put a stop to trials based on treason charges, and as a result no senators were put to death during his reign. He prevented judicial abuses by making it illegal for a person to be tried under different laws for the same offense. After the eruption of Mount Vesuvius, Titus provided financial aid from his own pocket to the survivors. The Colosseum, started by his father, was completed under Titus's reign, and the very eleborate inaugural games lasted for a hundred days.
Nerva (r. 96-98 CE): Upon Domitian's assassination, Nerva was elected emperor by the Senate, despite his lack of political or military experience and his relatively advanced age for the time (60 years old) and poor health. Nerva had a mild personality and was a benevolent ruler. He granted amnesty to those exiled or imprisoned under Domitian, allocated land to the poor, cut the inheritance tax, provided employment by repairing roads and aqueducts, and improved the standards of living of many Romans, which made him very popular with the people. Nerva abolished the Fiscus Iudaicus, the additional tax which all Jews in the Empire had to pay. He, however, never won over the army, who forced the childless emperor to adopt Trajan as his successor, thus making him the first emperor to adopt a son who was related to him neither by blood nor by marriage and the first successor from outside Italy.
Gallienus (r. as co-emperor 253-260 CE, as sole emperor 260-268 CE): His reign came at the height of the Crisis of the Third Century, when repeated plagues depleted the population, weakened the economy and allowed the invasions in Central Europe by the Alammani and the Goths, and by the Sassanid Persians in the East, which in turn caused many local revolts - one leading to the independence of the Gallic Empire under Postumus. Despite all these troubles, Gallienus managed to repelled more Germanic invasions than almost any other emperor and quelled nine attempts of usurpers of overthrowing him. He was extremely courageous, personally led his armies and was seriously wounded in battle at least twice, both times preventing him to deal with Postumus and recover the secessionary western provinces. Nevertheless Postumus appears to have been an able and trustworthy ruler and he reached an agreement with Gallienus that he wouldn't try to attack Italy and cause a civil war, and kept his word. Gallienus was a highly cultured and decent emperor. He showed clemency toward his enemies, pardoning a general (Aureolus) who revolted against him, settling Alamanni tribes he had defeated within the empire, and usually doing all he could to preserve peace in the long-run and avoid unnecessary bloodshed. He established a new model of governance conferring more autonomy to some regions of the empire, such as Egypt and Palmyra. His relationship with Odaenathus, semi-independent king of Palmyra, was so good that he always supported Gallienus and even defeated usurper in the East for him. Odaenathus had stopped the Persian invasion, but chose to remain loyal to Gallienus and remain under Roman rule even though he could easily have proclaimed his independence. Gallienus was the first emperor who appointed all his military commanders based on their abilities rather than their civilian rank. He also created Rome's first heavy cavalry force to fight against the Persian horsemen and archers. His 15-year reign was the longest wholly comprised within the 3rd century. He was also the last emperor of Italian descent and the last to rule from Rome.
Probus (r. 276-282 CE): One of Aurelian's best generals, he followed in his footsteps, kept the army disciplined and defeated countless barbarian incursions, put down three rebellions, encouraged the spread of viticulture to Gaul and the Balkans, and drained swampland in Egypt to increase the cereal production in what was the breadbasket of the empire. He pushed his soldiers too hard though, forcing them to work on land reclamations when they weren't fighting, which eventually led to his murder by his own troops. Gibbon sees Probus as the last of the benevolent constitutional emperors of Rome.
Majorian (r. 457-461 CE) : As soon as he took the throne, Majorian reformed launched ambitious reforms of legal system. He attempted to fight the declining birthrate among wealthy Romans due to the high number of women leading celibate lives within the Church. He passed a law to protect century-old public buildings from detorioration and to prohibit the removal of bronze statues and ornaments to refill the state treasury (which his predecessor Avitus had resorted to). His most ambitious plan was to heavily tax the rich in order to raise a sizeable army and fleet in order recover North Africa from the Vandals. Unfortunately his planned attack had to be abandoned after the Vandals got wind of it and launched a pre-emptive naval strike to sink the Roman fleet before he could even leave the port of Cartago Spartaria (modern Cartagena) in Spain. Majorian was assassinated by Ricimer, his magister militum, upon his return to Italy, probably under order of the Senate who hadn’t been pleased by the new taxes.
The competent but despotic emperors
Domitian (r. 81-96 CE): Titus's brother is often remembered for his authoritarian rule and his opposition to the Senate. He had over 20 senators executed and tried to curtail the Senate's power as much as he could. His main problem was his lack of trust and paranoia. However his harshness was limited to a highly vocal minority. Some historians have defined Domitian as a ruthless but efficient autocrat. For the majority of his reign, there was no widespread dissatisfaction with his policies. As Barry Strauss put it in his book Ten Caesars, Domitian was "a responsible financial steward, a fair-minded administrator of the provinces, and an able manager of border and defense policy. He gained popularity for his shows, banquets, and cancellation of debts. His gladiatorial games included such crowd-pleasers as night fights by torchlight and bouts between women gladiators. He was a great builder, too, whose projects included a new hippodrome, the outline of which is still seen today in Rome’s Piazza Navona." Philip Matyszak in Lives of the Romans describes Domitian as meticulous and conscientious, with a keen interest in finance, but a tendency to micromanage the government.
Septimius Severus (r. 193-211 CE): He restored order after the mess caused by Commodus, aptly reformed the legal system, raised three extra legions, created a mobile reserve army in northern Italy, and expanded the borders of the empire to their greatest extent. However, Severus was also harsh and selfish. He disregarded the Senate, had many senators executed, used public funds to build grandiose edifices in his native city of Leptis Magna. His reign was focused almost entirely on the military and he seriously debased the currency to pay his troops. His destruction of the Persian capital at Ctesiphon in 198 caused the overthrowing of the Parthian dynasty by the more brutal Sassanians, who would become a much tougher enemy for the Romans. Severus recognised the wicked nature of his son Caracalla, who almost murdered him once, but didn't prevent him from succeeding him, which ultimately placed a monster at the helm of the empire, when he could have exiled Caracalla and chosen his milder second son Geta as sole ruler instead.
Aurelian (r. 270-275 CE): He instilled great discipline in the Roman army (his coins remember him as Restitutor Exerciti, or Restorer of the Army) and recovered the the western and eastern provinces that had declared independence (Gallic Empire and Palmyrene Empire). He also defeated the Goths, Suebi, Vandals, Sarmatians and Carpi. Aurelian attempted to restore the Roman Empire to the glory of its heyday and showed great reverence for tradition and had relatively good relations with the Senate. He also built massive walls around Rome, which can still be seen today (although Maxentius doubled their height later). He was loyal, incorruptible and inspired loyalty from his men and from the Senate and there was never any serious rebellion against his rule. On the other hand, Aurelian has been described by ancient authors as stern, ruthless, bloodthirsty and excessively cruel. He had servants executed in front of him for committing adultery, and even executed his sister's child for unknown reasons. He introduced the cult of Sol Invictus ("the unconquered Sun") to Rome and attempted to make it the main religion, subordinating all other gods to the Sun. His only building projects, apart from the new city walls, was a magnificent Temple of Sol Invictus in central Rome and the organisation of grandiose games (Agones Solis) in honour of the Sun held every four years from 25 December (anniversary of the temple's consecration). That date was taken over by the Christians for Christmas a few generations later. Although Aurelian wasn't the first emperor to worship the sun, he was the first to adopt the mention Sol Invictus on his coins and obliged the legions to adopt the new deity. Aurelian was also the first Roman emperor to call himself a god was still alive and had himself called Dominus ("Lord"), a term re-used by Diocletian and later emperors of the Dominate, when emperors started behaving like kings.
Diocletian (r. 284-305 CE): Acclaimed for saving and re-organising the empire and establishing the Tetrarchy, Diocletian was also a brutal ruler who changed the nature of the Roman Empire into what is known as the Dominate, granting the emperor divine status and in which the state should serve the emperor rather than the other way round. Diocletian also persecuted Christians and issued a edict trying to fixing maximum prices for goods, which had disastrous economic consequences.
The good emperors turned bad
Caligula (r. 37-41 CE): Exemplifying the sexuallu deviant and insane emperor in the collective imagination, Caligula was actually beloved by everyone during the first seven months of his reign. He was the son of Germanicus, one of the greatest and most popular generals in the early imperial period. Caligula was very intelligent and implemented much needed public reforms. He destroyed Tiberius's treason papers, declared that treason trials were a thing of the past, and recalled those who had been sent into exile. He helped people who lost property in fires, abolished certain taxes, restored the practice of democratic elections. Caligula completed the temple of Augustus and the theatre of Pompey began an amphitheatre beside the Saepta and expanded the imperial palace. He began the aqueducts Aqua Claudia and Anio Novus, which Pliny the Elder considered engineering marvels. But then he got very ill with high fever - probably meningitis, although some claim he was poisoned. He survived, but his personality changed and this is went he started acting erratically, becoming increasingly wicked and cruel, getting into fits of anger and killing people on a whim. Among the close family members he had executed were his cousin and adopted son Tiberius Gemellus, his father-in-law and his brother-in-law, while his two surviving sisters were exiled. Eventually, officers of the Praetorian Guard assassinated the mad tyrant and named his uncle Claudius emperor.
Nero (r. 54-68 CE): Nero's reign would have been lauded as one of the best if he had ruled only for seven years. That was in all likelihood thanks to the guiding influence of his mother, Agrippina, who was the real power behind the throne in his teenage years. Cultural life flourished under his reign, while his generals won the war against the Parthians and crushed Boudica's revolt in Britain. The second half of his reign went downhill fast after someone convinced him that his mother was plotting to murder him and he had her assassinated. After that he lost his mind and retreated in artistic activities and delusions of grandeur, eventually thinking of himself as a living god, but still deeply insecure about his own ego and in constant need of approval from the public. Nero's image was reviled by the Christians in retribution for the persecutions he ordered after the Great Fire of Rome in 64 CE.
The paranoid and withdrawn emperors
Tiberius (r. 14-37 CE): An excellent general in his youth, Tiberius was already 56 years old when he became emperor. That made him an experienced administrator and he managed to keep the Pax Augusta, secured the borders of the empire and had a generally stable reign that saw increased prosperity for Roman society. He was humble and refused to bear the titles Pater Patriae, Imperator, and Augustus. However, Tiberius had poor relations with the Senate and often acted as a tyrant, having dozens of Senators executed. His family life wasn't much better. He had his adopted grandson and heir Nero Julius Caesar and Drusus Caesar and their mother Agrippina the Elder exiled and possibly executed soon afterwards. Increasingly embittered with his position of Princeps, Tiberius retired to his villa on Capri for the last 10 years of his reign, leading a debauched life, and leaving during that time in command the Praetorian prefect Sejanus, who acted a a tyrant toward the population of Rome.
Commodus (r. as co-emperor 177-180, as sole emperor 180-192 CE): Commodus was only 18 years old when he became sole emperor upon his father's death. Inexperienced and uniterested in the matters of state, Commodus led a debauched lifestyle and surrounded himself with friends who were a bad influence on him. The worst among them was the former slave Cleander, who became his favourite, chamberlain, then Praetorian prefect. Cleander allegedly misappropriated Rome's grain supply to enrich himself, causing a famine in the city and his downfall. Escaping several assassination attempts, Commodus grew increasingly paranoid and withdrawn, trusting only a small circle of former slaves, including his concubine Marcia. In the last two years of his reign, Commodus became megalomaniac, comparing himself to Hercules. After the fire of Rome in 191, he declared himself the new Romulus, ritually re-founded Rome, renaming the city Colonia Lucia Annia Commodiana and the Roman people were now called the Commodiani, while the legions became the Commodianae. Commodus held 14 days of games at the Colosseum in which he fought as a gladiator in fixed matches against wounded soldiers and amputees, winning all the fights. For each of his appearance in the arena, he charged the city of Rome a million sesterces, straining the Roman economy, until he was finally assassinated.
The worst emperors
Caracalla (r. 198-217 CE): A cruel brute who had his own 22-year-old brother Geta murdered because he didn't like him, then had 20,000 of his brother's sympathisers persecuted and executed. When the inhabitants of Alexandria heard of Caracalla's claims that he had killed his brother, Caracalla massacred the crowd assembled before the city to greet his arrival, before setting his troops against Alexandria for several days of looting and plunder. He executed his father-in-law and exiled his wife. Obsessed by war, he depleted the state treasury and debased the coinage to pay for his military expeditions. Worst of all, he granted Roman citizenship to all free people in the empire. Until then Roman citizenship had been used as an incentive for (foreign) auxiliary troops and provincial administrators to work well and earn their citizenship, which was a sort of special status conferring prestige to a family. Caracalla eliminated all meaning to Roman citizenship by making it universal (except for slaves), which completely destabilised the way Roman society functioned in the long term.
Maximinus Thrax (r. 235-238 CE): He was a big brute who assassinated the young emperor Severus Alexander (to whom he owned his command of Legio IV Italica) and his mother (and regent) Julia Mamaea, just because the emperor had negotiated a peace treaty with the Alemanni. He was not just the first emperor who didn't hail from the senatorial or equestrian class, but he was of particular low birth. He immediately doubled the pay of his soldiers, for which he had to increase taxes and resort to violent methods and illegal confiscations. He had the close advisors of the previous emperor put to death and managed to launch persecutions of Christians on a large scale during his 2 year reign. According to the Historia Augusta: "The Romans could bear his barbarities no longer – the way in which he called up informers and incited accusers, invented false offences, killed innocent men, condemned all whoever came to trial, reduced the richest men to utter poverty and never sought money anywhere save in some other's ruin, put many generals and many men of consular rank to death for no offence, carried others about in waggons without food and drink, and kept others in confinement, in short neglected nothing which he thought might prove effectual for cruelty – and, unable to suffer these things longer, they rose against him in revolt."
Constantine (r. as Western Caesar 306-309, as co-Augustus 309-324, as sole emperor 324-337 CE): Constantine was defined above all by his ruthlessness. He killed his two brothers-in-law in order to become sole emperor, effectively destroying the tetrarchy system established by Diocletian. He later had his oldest son and heir, Crispus, executed for an unproven affair. Constantine was the first Christian emperor and although he didn't dare make Christianity the official religion of the empire yet, he did all he could to subsidise Christianity with the taxes from pagans and granted exceptional powers to Christian bishops. He is basically responsible for the collapse of traditional Roman cult and values. He also disbanded the Praetorian Guard, moved to capital to Byzantium, which in a megalomaniac fashion he renamed after himself Constantinople. Constantine created a Police State, a large and corrupt administration (a "Byzantine" administration as it later became known) and reinforced the hereditary class system introduced by Diocletian. He formalised the distinction between the frontier army and the better paid mobile army, a decision which the Greek historian Zosimus claims was responsible for the ultimate collapse of the Western Roman Empire.
Constantius II (r. as Caesar 324-337, as co-Augustus 337-350, as sole emperor 350-361): One of Constantine's three sons to share the empire after his death, Constantius oversaw the massacre of eight of his relatives almost immediately after becoming emperor. After the death of his two brothers, he became sole Augustus of the Roman Empire. His reign was one of the longest (24 years + 13 years as Caesar), yet he was by any standards one of the worst emperors in history. In his book The Last Pagan: Julian the Apostate and the Death of the Ancient World, Adrian Murdoch describes Constantius like this: "Although he was a dull, rather uncharismatic emperor, most interpretations have seen him as at best an incompetent, at worst a paranoid monster. [...] He was not intellectually gifted, one of the reasons he hid behind the pomp and ritual of the court. An out-and-out monster he might not have been, but there was a nasty and sneaky aspect to his character. In one of the more subtle analyses of his character, several comment that Constantius was much better at fighting civil wars than actual wars. [...] Constantius was overly influenced in his decisions by the people who surrounded him; the courtiers and the eunuchs who made up the court. Julian was later to refer to “the wild beasts that surrounded him and cast their evil eyes on all men”, while a bishop more elegantly, but no less harshly, wrote: “I find that he does not possess common understanding, but that his mind is solely regulated by the suggestions of others and that he has no mind of his own at all.” "
Theodosius (r. as Eastern emperor 379-392, as emperor of the whole empire 392-395): Theodosius is mostly remembered for making Christianity the official religion of the empire and banning all pagan religions, including traditional Roman religion. He thus started a new era of intolerance and persecution, which hastened the decline of the Roman Empire. He is responsible for the destruction of most ancient Greek and Roman temples, including the Serapeum of Alexandria, which was the heir of the Great Library and the largest library in the world at the time. In other words, Theodosius continued Constantine's work and destroyed what was left of the original ancient Roman culture. He decreed that the empire should be divided between his two sons, Arcadius (Eastern empire) and Honorius (Western empire), and the empire would never be reunified again.
Honorius (r. 395-423): Theodosius's son, Honorius was as much of a religious persecutor, but with an additional xenophobic slant. He seems to have hated anyone of Germanic descent, even his best general, Stilicho, who was half-Vandal half-Roman, but born and raised in the empire as a Roman. His top general, Stilicho, who had successfully negotiated a peace with Persia and defeated all barbarian invasions during his long career, never losing a single battle, was imprisoned by Honorius and executed in 408 without a fair trial. This was followed by a pogrom against all and any Germanic people living in Italy, including the thousands serving in the Roman army, which Honorius couldn't stand. This left the Western Empire virtually defenceless, allowing the Suebi, Vandals, Alans and Burgundians to carve their own kingdoms within the borders of the empire, then Alaric to sack Rome in 410 and the abandonement of Britain by the Romans the same year. Honorius's bigotry, racism, narrow-mindedness and incompetence hastened the fall of the Western Roman Empire. In fact, there was hardly anything left of the Western Empire outside of Italy after his reign.
Valentinian III (r. as Western emperor 425-455): Emperor at the age of 6, Valentinian III was a weak emperor, dominated most of his life by his mother Galla Placidia and later by his best general Flavius Aetius. From the 430's until hid death in 453, Aetius managed to crush 11 rebellions, including those of the Burgundians, Bacaudae (peasant insurgents) and Visigoths in Gaul, to seal a peace treaty with the Vandals after their capture of Carthage, and defeat the Hunnic invasion of Gaul in the Battle of the Catalaunian Plains. Aetius's skills as a military commander and his ability to negotiate with barbarians saved the Western Roman Empire from implosion several times and kept in check the various Germanic kingdoms settled within the empire's borders (Franks, Burgundians, Visigoths, Suebi and Vandals). In 454, Valentinian was convinced by the jealous Roman senator Petronius Maximus and the chamberlain Heraclius to assassinate Aetius. Valentinian killed Aetius himself during a private meeting with him. This event caused Germanic tribes to relinquish their peace treaties with Rome and precipitated the collapse of the empire. The Vandals sacked Rome 9 months after Aetius's assassination. In the 23 years that followed Aetius's death, a succession of weak and short-lived emperors had to witness to disintegration of the empire until a Germanic leader, Odoacer, deposed the last Western Roman emperor in 476.
Why teenagers make bad emperors?
What Caligula, Nero and Commodus all had in common was that they were inexperienced teenagers when they inherited the title of emperor. Earlier emperors or the Senate should have established a rule that emperors should, like consuls of the Republic before, have reached a minimum age (42 years old for consul) and have a certain level of experience like the old cursus honorum. In case the heir was underage he should have been appointed one or several regents.
Youth and inexperience is one factor that creates bad emperors. Another is to inherit the name of one or several famous emperors. That was the case of Caligula (officially known as Gaius Julius Caesar Augustus Germanicus) and Caracalla (Marcus Aurelius Severus Antoninus Augustus) and I am convinced that this played no small part in boosting their ego to megalomaniac proportions. Bathing in the glory of their namesake (adopted) ancestors, they felt no need to prove their abilities to make a name for themselves and instead immediately took the throne with a sense of entitlement.