INTRODUCTION

Rome started out as a very ordinary village on the Tiber river in central Italy perhaps a millennium before our story begins. For centuries, it was largely indistinguishable from its neighbours but, in the fourth century BC, it began aggressively to expand into the rest of the peninsula. Its leaders were magistrates elected each year by a citizen population whose votes were weighted to give the rich and powerful a decisive voice in their outcome. The system was in some respects genuinely representative of the citizenry’s wishes and, virtually every year, the citizen army marched out, led by two elected consuls, to fight an enemy. Conquest accelerated in the third century BC, and a hundred years later Rome was unquestionably the superpower of the Mediterranean world. At the same time, however, the republican constitution began to break down, as rival generals tried to grab a monopoly of power for themselves and their cronies. The republic was destroyed by decades of civil war and, by the end of the last century BC, the sputtering machinery of republican government was replaced by the rule of one man, Augustus, the first Roman emperor.

Augustus, as he was known from 27 BC onwards, had started life as Octavianus, the great-nephew and adopted son of Julius Caesar, the first republican warlord to attempt to rule the Roman world alone. Caesar was assassinated for that presumption, but the republic was not restored, and the wars that followed his murder in 44 BC were even bloodier than those that preceded it. By the time they finished in 31 BC, the Roman world was exhausted, its far-flung provinces having been battlegrounds for three generations. Autocracy was welcomed as an alternative to more civil strife, and the fractious, ramshackle but representative constitution of the republic disappeared for good. Augustus outlived both his own generation and most of the younger one, too; by the time he died, very few people alive could remember the world before he ruled it. He styled himself the princeps, the ‘first man’ in the Roman state, rather than ‘king’ or ‘emperor’. That polite fiction soothed the feelings of senators, the body of former magistrates who had long been accustomed to dominating the state. But the total hold he kept on actual power, and his preternatural longevity, allowed Augustus to transform Roman government.

We draw a line between Roman republic and Roman empire at the reign of Augustus to distinguish a Rome ruled by elective magistrates from one ruled by an individual autocrat, but the republic had already possessed a vast empire in Europe and the Mediterranean. This republican Roman empire was ruled by the Romans for the benefit of Italy, where a large majority of Roman citizens lived, and for that of the city of Rome, the largest conurbation the world had ever seen. The Augustan revolution gradually changed that. Republican provincial government, particularly in the immediate aftermath of Roman conquest, was frequently capricious and always rapacious, even when it brought new infrastructure and economic opportunities in its wake. Under the rule of the emperors, provincial life became rather more stable. The chieftains, burghers and nobles who ruled the empire’s indigenous populations were free to retain their local authority, with two simple provisos. Peace must be kept and Roman citizens allowed to go about their business unmolested, and the state treasury must be kept full. This was a bargain that local elites eagerly seized, from the chieftains of western Europe to the Greek town councils and local dynasts of the eastern provinces. They and their subjects learned to make Roman governors happy, and many learned how to live like Romans. The enthusiasm of local elites for imperial rule, and for the peace that it brought, is the primary explanation of the Roman empire’s success.

Augustus and his successors did more than reward collaboration. They also accepted many provincials into the ranks of Roman citizens. That was important. No other ancient state was as free with the privileges of its citizenship as was Rome under the emperors. Rather than guard citizenship for an imperial core, emperors granted it widely: sometimes to individual big men whom they knew personally; sometimes to favoured cities; sometimes to entire regions of the empire. This meant that from one end of the empire to another there were men who shared in legal rights that only Roman citizens possessed. They were equal before the law wherever they went in the empire, and their property and personal rights were valid regardless of the local jurisdiction in which they happened to live or find themselves. Readers may recall the story of the apostle Paul who, when threatened with a trial before hostile Jewish authorities, invoked his Roman citizenship and had his case transferred to Rome. This ‘internationalism’ of Roman citizenship was perhaps its greatest value.

In the course of the first century AD, the empire was transformed from a collection of subject territories exploited by Rome and Italy into a mosaic of culturally diverse provinces, all subject to the Roman emperor and now increasingly populated by provincial Roman citizens. Iberians and Gauls, Moors and Syrians, Thracians and Greeks – these and many other peoples could increasingly think of themselves as Romans, whatever else they might be as well. That self-identification, the sense of being Roman, became deeper and stronger in the centuries covered by this book: provincial Romans will gradually take centre stage in the political history of the empire. The Romans of the city of Rome will remain important, too, particularly the mass of the urban population known as the plebs. When Augustus imposed his autocracy, the plebs traded its right to participate formally in politics and choose its leaders in exchange for peace, prosperity and pomp: what the satirist Juvenal mocked as the ‘bread and circuses’ that kept the people quiet. It was a bargain the plebs could accept, but it did not come cheaply for the emperor. Cultivating the urban population meant not just money but also ‘face time’. A princeps who cheated the plebs of either handouts or personal attention could expect rioting in the streets.

To make sense of our narrative, we need to pay attention not just to the imperial senate, or the urban plebs, or the Roman citizens in the provinces, but rather to the way all of them, together with the emperor and the army, fitted into the empire’s system of governance, its unwritten constitution. This was deliberately ambiguous, because Augustus was extremely reluctant to expose the reality of his domination. The senate, whose members had once governed the republic and its provinces, accepted the autocracy of the new princeps not just because it brought peace, but because he put up a decent facade of deference to old republican principles. Senators could continue to hold offices with republican titles – quaestor, aedile, consul – even though they could no longer compete freely to win them, and they remained vital to the administration of the empire. As genuine memories of the republic faded, and those who had experienced its last decades died out, elite citizens could accept the political theatrics that cloaked the reality of one-man rule. They also accepted hereditary succession, which is slightly more surprising.

The republic’s founding myth was the overthrow of the last king, Tarquin the Proud, supposedly in the sixth century BC, and the establishment of a senatorial government in which elected magistrates held office for just one year at a time. The word rex, ‘king’, remained a potent insult in republican politics till the end; the belief that Julius Caesar might in fact make himself king was one of the main justifications for his assassination. But though Augustus was squeamish about the language with which his power was described, neither he nor his subjects shrank from the reality of hereditary succession, as if the emperors were indeed monarchs. Augustus handed the state on to his adopted son Tiberius (r. AD 14–37), thus establishing the dynasty we call the Julio-Claudians, named after the two republican clans from which they descended. Three more members of that family succeeded Tiberius. When the male line of the Julio-Claudians was exhausted, in AD 68, there was a brief interval of civil war before its victor, Flavius Vespasianus (r. 69–79), established a new imperial dynasty that we call Flavian. By doing so, he proved that the empire could continue without its founding family, and that emperors could be created outside the city of Rome, by the army and in the provinces. This revelation was what the senatorial historian Tacitus called the arcanum imperii, ‘the secret of empire’. It meant that other families could perpetuate the Julio-Claudian autocracy if they could win it on the battlefield.

The transition to a new dynasty made the real basis of imperial power more transparent. Vespasian had first been proclaimed emperor in a putsch by the provincial legions of the east, but was then acclaimed by the senate and people of Rome, which served to legitimise the accession. More significantly, the senate voted Vespasian a package of specific magisterial powers that had been exercised by the Julio-Claudians. These were powers that set the princeps apart from everyone else in the state, the foundation on which he claimed the right to act. Based on powers that the republic’s elected magistrates had exercised during their time in office, their combination in one person gave the emperors their potency. Two powers were most important. The first was proconsular imperium. Under the republic, former consuls went out to govern the provinces as proconsuls, ‘those acting for (pro) the consuls’ in Rome. Proconsuls could conduct foreign policy, administer law and justice to citizens, and command obedience from citizens and non-citizens alike, but could do so outside the territory of the city of Rome in which the same powers were held by the annual consuls. What made the proconsular imperium of Augustus and his successors different was its extent: the princeps had proconsular imperium superior to that of any provincial governor, which made his every decision binding wherever in the empire he chose to act. The second of the two essential imperial powers was likewise rooted in republican history. The princeps possessed perpetual tribunicia potestas, which had been the right of a republican tribune to veto laws inside the city of Rome and command citizens within the sacred limits of the city. Like consular authority, tribunicia potestas under the republic was exercised for the single year in which a man held the office of tribune. But under the emperors, no one save the princeps possessed tribunicia potestas, and he possessed it in perpetuity.

When the senate voted to give Vespasian tribunicia potestas it confirmed that there were things the princeps possessed by virtue of his position not his person, and that the powers held by Augustus could be held by someone not of his family. But that was not the same thing as working out rules for how one actually became emperor; it only meant that whoever succeeded in being recognised as emperor, whether by heredity, by coup d’état or by military victory, would necessarily come to exercise those powers. But the ambiguity remained, because the fiction that Augustus had restored the republic made it impossible to specify precisely just what gave a Roman emperor his power to rule. For centuries, some combination of army, senate and people was needed to make a man emperor, but the balance between them was never clear and never subject to transparent or formal rules. Dynastic succession became the baseline norm, but it was never a principle: the empire was an autocracy with frequent hereditary succession, but it was never a hereditary monarchy.

The army, which we have mentioned only in passing thus far, was as crucial to making and unmaking emperors as were the senate or the Roman people. Imperial Rome’s soldiers were long-serving professionals who enjoyed privileges that set them apart from the wider population of both citizens and provincial non-citizens. The goodwill of the soldiery needed constant tending because, in the final analysis, the success of the imperial autocrat depended on that goodwill: it was the loyalty of the armies, particularly the great provincial armies in Britain, Germany, the Balkans, Anatolia and Syria, that protected the princeps from challenges. Even more important was the loyalty of the praetorian guard, the emperor’s personal troops quartered in Rome, who were invariably lethal when their ruler displeased them. Yet the soldiery’s needs were generally predictable, as too were those of the Roman plebs.

The elites – the senators in particular – gave the emperor much more trouble, because they had to be handled as individuals, not propitiated as a group. To administer the empire, the emperor relied on an oligarchy of the rich and well born – the senators – and those who were merely very rich – the equestrians. The senatorial element in this oligarchy was self-reinforcing: holding certain magistracies conferred senatorial status, and that status accrued to a family for three generations, even if it was not sustained by office-holding in a particular generation. A senator needed to have a minimum fortune of a million sestertii to retain his senatorial status (an average townsman could live well on a thousand or so annually) and many senators actually had incomes that exceeded that figure every year. Given this exclusivity, there was a natural tendency for senatorial families to behave as a class apart from the rest of society, the ordo senatorius, but it was never a closed shop, precisely because of the connection to money.

Wealthy citizens who possessed a suitable net worth could choose to pursue the magistracies, starting with the office of quaestor, which conferred actual participatory membership in the senate. These wealthy men belonged to a second group within the larger Roman oligarchy, the equestrian order, or ordo equester (the name goes back to very early Roman history, when it referred to men with enough money to serve in the cavalry). Unlike senators, who needed to hold specific magistracies to confirm their status, equestrian status was an automatic consequence of a certain minimum fortune (400,000 sestertii). One was an eques by virtue of being, not of doing, and one remained equestrian whether one sought office or not. By the time our story begins in the next chapter, under the emperor Hadrian, the senatorial and equestrian ordines formed an international governing elite, into which new blood was incorporated whenever Roman citizenship was granted to a new provincial population: rich non-citizens would suddenly be transformed into Roman equestrians, eligible to seek a place in the senate if they so chose. Over time, it was the equestrian element in the oligarchy that came to predominate, occupying more and more of the offices through which the empire was administered. But the essential point is that the flexibility with which the ruling elite coopted new members into itself made for a basically stable oligarchic regime without which the emperors simply could not rule.

That is why, in the pages that follow, we cannot confine ourselves to discussing the emperor or the imperial family, and why we will not shy away from introducing a great many Romans, with their long, often unmemorable, names: these generals and bureaucrats, financiers and orators, made the empire what it was, even though they can be shadowy figures, known to us only by the long series of offices and commands that they held. Their motives, let alone their personalities, are often completely invisible. Yet to leave them out of the story, as popular histories sometimes do, is to simplify things in a way that cheats the reader and traduces the reality of the past: without reference to these oligarchs, with their complicated names and complicated careers, imperial history becomes a fantasy world in which only the emperor and the emperor’s family count. They did count, of course, but the oligarchy counted just as much: autocracy could only work through, and with the consent of, its oligarchs.

It was a mutually re-enforcing relationship, but one we can get at only some of the time, because our sources for different periods of Roman imperial history are highly variable, both in quantity and quality. Readers will soon realise that we can narrate some eras in exponentially greater detail than others: the middle of the second and end of the third centuries, for instance, are almost a blank; the end of the second and beginning of the third are well documented. But there is another source problem besides the uneven distribution of evidence. Almost all the narrative sources we have are the work of senators or authors who identified with the senatorial order. For that reason, they tend to focus on the personalities of individual emperors, and the impact these had on the life of the senate and Rome itself. The emperors Caligula and Nero were horrible to senators and bad to the senate, so therefore they were tyrants, despite the fact that the latter was genuinely very popular in much of the wider empire. By contrast there is the stock type of the good emperor, the civilis princeps, who imitated Augustus as a well-mannered first among senatorial equals. Our elite historical traditions, then, tend to place every emperor into one stock type or the other. Good Vespasian’s younger son Domitian followed the ugly pattern of Caligula and Nero. Vespasian and Trajan offered polite form its due deference and thus were fondly remembered. For all the concentration of our narrative sources on the character of the empire, we need to pay attention to the other evidence available, especially the vast number of inscriptions on stone that give us insight into how thousands of otherwise unknown individuals presented their lives and careers to the world. When we do that, we nearly always find that the emperor’s personality, and the way the upper strata of the oligarchy experienced his rule, bore remarkably little relationship to the fortunes of the empire as a whole.

That was already true under the Julio-Claudians and it was even more true when our main narrative begins, in the year 117, with the death of the emperor Trajan and the accession of his distant relative Hadrian. To understand the reign of Hadrian, which in many ways determined the dynastic history of the whole second century, we need to sketch briefly the events of Trajan’s time, and the sort of men who were now dominant in the ruling oligarchy. Vespasian and his sons were the first emperors not to have been Romans of Rome, hailing instead from an Italian municipality. They were descendants of Italians who had been granted Roman citizenship during the last century of the republic, and the family was senatorial on one side, equestrian on the other. This was novel. The Julio-Claudians were descended from two great senatorial clans of the late republic, and that contributed to the sense of their legitimacy and power. But under their dynastic rule, the old distinction between Roman citizens from Rome and Roman citizens from Italy came to matter much less, as the latter reached increasingly high positions in imperial government.

When Vespasian came to power, there was some sneering about country bumpkins that Vespasian seems to have revelled in, but no one thought his background made him unsuited to rule. And under his Flavian dynasty, a similar levelling of regional distinctions began to be felt outside the Italian peninsula. Colonial elites from southern and eastern Spain and from southern Gaul, descendants of republican veterans settled in the provinces they had conquered, began to enter the senate in growing numbers. A group of Spanish senators had already clustered around the court of Nero, while Roman senators from Gallia Narbonensis were so assimilated into the Italian aristocracy that it is notoriously hard to distinguish the two groups in the surviving evidence. As Italian elites had seen their prospects rise and broaden under the Julio-Claudians, so too did those of colonials under the Flavians. With the extinction of the Flavians, the new importance of the colonial elites became clear.

Vespasian’s younger son Domitian was assassinated in September 96. There was no civil war like the one that followed the suicide of Nero, the last of the Julio-Claudians, in 68. Instead, the senate acted quickly and made Marcus Cocceius Nerva emperor. He was old, respected and childless, and his career went back deep into Nero’s reign. His senatorial peers loved and trusted him. But he was unpopular with the plebs and the praetorian guard, and he was also weak and indecisive. The armies on the frontiers became restive. It seemed only a matter of time before one of the great commanders staged a coup like the one that brought down Nero and started a civil war. Rumours spread, but months passed and no coup came. We need to imagine the machinations taking place behind closed doors, because what really happened was carefully veiled from posterity. But seemingly out of the blue, in AD 97, Nerva announced the adoption of a powerful general, Marcus Ulpius Traianus, as his son and imperial partner. Known to us as Trajan, he was a Spaniard from Italica in Baetica, the rich southern province centred on the city of Corduba (modern Córdoba). The adoption had the desired effect, calming the soldiery with a man it was happy to call emperor. The senate, too, was pleased, and Trajan bent over backwards to be the very model of a civilis princeps, the antithesis of Domitian, an emperor whom he had in fact served quite faithfully.

Nerva soon died – naturally, by all accounts – and as sole emperor, Trajan (r. 98–117) deferred to the senate wherever possible, granting considerable discretion to senatorial commanders and provincial governors. We are fortunate to possess the letter collection of C. Plinius Caecilius Secundus, better known as Pliny the Younger, whose correspondence with Trajan gives us a window into the relationship between an emperor and a senatorial proconsul. Pliny is deferential, exaggeratedly worried not to take decisions that might displease the princeps. Trajan is exaggeratedly patient with his governor’s indecisiveness, his repeated requests for guidance in small matters as well as large. The princeps knows that courteous tolerance behoves him when writing to a social peer. And the princeps also knows his instructions matter. Again and again, he reminds Pliny to share the genuine solicitude for the provincials that he himself feels as princeps, to let them live their lives in peace, to stop them hurting one another.

Trajan was forever remembered as optimus princeps, the best of emperors, and not just because he flattered the self-regard of senators. He manifestly protected the safety of his subjects and he brought new glory to the name of Rome, fighting a massive war on the Danube against the Dacian king Decebalus, and expanding imperial territory into the Carpathians by creating three new provinces in Dacia. These trans-Danubian provinces gave Rome control over the important mines of Transylvania and also made it possible to supervise barbarian client kings to the east and the west of the Carpathians. Dacia’s subjugation made Trajan that rare thing among emperors, a propagator imperii, one who had extended the boundaries of the empire. Indeed, the epithet optimus was not simply posthumous – it appeared during his lifetime, an adjective sometimes treated as if it were part of his actual name.

The picture was complicated by the ambiguity of the imperial succession that we looked at above. Trajan had no children and he hesitated to designate a successor: the optimus princeps could hardly reveal his autocracy with an act of blatant dynasticism. At the same time, the absence of a clear succession plan could end in disaster, as the aftermath of Nero’s reign had made clear. Moreover, if no heir apparent was designated, people would still speculate and factions would arise at court, with unpredictable consequences. Trajan compromised, unwilling to drop his persona as first among equals. He had one close male relative, Publius Aelius Hadrianus, the son of a maternal cousin and a product of the interlocking marriages among the Spanish colonial elites. Hadrian’s father, Publius Aelius Afer, had died in AD 86, at which point the young Aelius Hadrianus and his elder sister Domitia Paulina became Trajan’s wards. We are told that Hadrian was treated ‘as a son’ by Trajan throughout his life, that is to say, even from before he was clad in the toga virilis, the ‘toga of manhood’ that marked the passage from childhood to adulthood for a Roman male.

Trajan then brought the families of the Ulpii and Aelii even closer, by marrying Hadrian to his great-niece Sabina (she was the granddaughter of Trajan’s sister Marciana). Marriage connections were the way Roman elites sustained themselves in a world of low life expectancy and high puerperal mortality: Hadrian’s marriage to Sabina was consequential, but so too was that of his elder sister Domitia Paulina to the prominent general L. Julius Servianus, heirs to whose line would emerge into the political limelight throughout the second century. Trajan heaped honours on the women of his family, consciously echoing Augustus, who had done the same with his wife Livia. Thus Trajan’s wife Plotina was given the title augusta, as was his sister Marciana, and thenceforth the senior women of the ruling family were generally designated as augustae. When Marciana Augusta died in 112, she was deified by the senate, after which Trajan conferred the title augusta on her daughter Matidia. Hadrian was thus married to the daughter of an augusta and the granddaughter of the deified empress, Diva Marciana.

While all this seemed to single Hadrian out as Trajan’s heir apparent, there were counterindications as well. Trajan had not allowed his young relative special preferment on the cursus honorum (the phrase, literally ‘the path of honours’ or the ‘series of offices’ held by members of the Roman oligarchy, is untranslatable). This cursus honorum led through a number of minor qualifying offices and then into a series of magistracies that went back to the era of the republic: quaestor, aedile, praetor. Those who had served as praetors would go on to provincial governorships and then sometimes win the consulship after they reached the age of forty-four. As with the consulship, each of these traditional offices had a minimum age at which it could be held, and an interval between offices was enforced according to rules established by Augustus (these rules were called the lex annalis). For a man to hold an office in the first year he became eligible to do so was a great honour for which senators competed, but under the Julio-Claudians and Flavians, young members of the ruling dynasty were frequently exempted from the lex annalis, allowing them to leapfrog the normal sequence and hold offices well before those who were in theory their senatorial peers. Trajan did not allow Hadrian to do this. Presumably the emperor wanted to demonstrate his respect for the senate as a whole and the rules that bound all its members, but it also confused people. There were secret whispers that Trajan did not really think too highly of his ward.

It took until the year 113 for Hadrian’s status as Trajan’s likely heir to be secure, when he was designated to accompany Trajan on campaign as legatus pro praetore, which is to say an imperial comes (‘companion’) and special adviser. By 113, the ageing ruler had decided to launch another war of conquest. He was a restless man who disliked inactivity and preferred life in the field. His wars in Dacia had covered him in glory, and the lure of a war in the east was hard for him to resist. There were historical reasons for that allure, alongside the personal ones. Rome’s eastern neighbour was the Parthian empire, the only other organised state in the Mediterranean or Near Eastern world in this period. The Romans had regarded the Parthians as their great ideological foe since at least 53 BC, when the great republican general Crassus was killed on the battlefield at Carrhae and several Roman legions were annihilated alongside him. Since then, any victory against Parthia had been regarded as moral as well as military, even though the Parthians tended not to reciprocate the Roman hostility. To follow in the footsteps of Alexander the Great, to finally avenge the death of Crassus, that was a worthy project for the optimus princeps.

Trajan’s excuse was rivalry among claimants to the Parthian throne and Parthian interference in Armenia. In the early second century, Armenia was a client kingdom lying uneasily between the two great empires. Culturally, it was closer to Parthia, and its native dynasty shared the Iranian religion of the Parthian kings. Politically, however, it had long fallen within the Roman orbit and its kings were traditionally approved by Rome before being allowed to govern. Now, the Parthian king had deposed the Roman appointee in Armenia and installed a new ruler. That furnished Trajan with the only pretext he needed, and so, in 113, he launched an invasion of the Parthian empire with the explicit goal of conquering it and adding it to the Roman state. Hadrian’s true position as heir apparent became clear on this campaign.

The emperor was sixty-one when the Parthian campaign began, old for a Roman, and he could not be expected to outlive it. The campaign itself was a great success, at least in military terms. Armenia was rapidly brought to heel, while petty kings flocked from deep in the northern Caucasus to swear their allegiance to Trajan. The Roman army then marched down the Euphrates river, capturing every city it passed. The Parthian capital at Ctesiphon fell, and with that, Trajan had excelled any previous Roman general. It was not enough him. He pressed on further south, to where the Euphrates meets the Tigris and they progress together into the Persian Gulf. There Trajan stood looking out, lamenting that he was too old to follow Alexander’s ghost all the way to India. He would have to remain content with having placed a new king on the Parthian throne and mastered Rome’s great rival.

The emperor’s achievement was not quite all that it seemed. Before he had even left the Tigris island, near modern Basra in Iraq, eastern affairs were in disarray. Almost the whole of the conquered Parthian territory, and some of the allied kingdoms, was up in arms. More worryingly, the Jewish diaspora inside the Roman provinces had exploded into rebellion and proclaimed a Jewish king, a sign of dangerous messianic expectations. As was normal Roman policy, revolt on such a scale demanded overhelming reprisals. Trajan sent his best commanders to deal with the Jews, while he himself marched back through Mesopotamia into Roman territory, putting down the Parthian rebellions with great savagery. His health was failing and there was no obvious way to salvage the situation. Mesopotamia and Armenia would have to be written off. As he headed back into Roman Asia Minor, Trajan became too ill to travel and he died at Selinus in Cilicia on 8 August 117. Word of his death was covered up until Hadrian could be notified and presented to the soldiers, who duly acclaimed him. With the accession of Hadrian, our main story can begin.