Megalomaniac Emperor Caius ‘Caligula’ had seen himself as a god and used the Temple of Castor in the Forum as the entrance to his palace. Nero had built a colossal statue of himself as the sun-god Helios and ruled as a sun-king from his ‘Domus Aurea’ in the mid-60s, and Domitian in the 80s had ruled as ‘dominus et deus’ (‘lord and god’) and built a large throne-room in the Imperial residence on the Palatine. This fitted in with Eastern notions of the ruler as semi-divine but not with Roman practice; it was a different matter from so-called ‘Emperor-worship’, a universal practice in the Early Empire which was more a matter of a cult of respectful loyalty to the status of the ruler than treating him as divine. On all three occasions this innovation had been reversed by their successors, so the same could have been done to Diocletian’s ‘Oriental’ Court.
But instead Constantine continued the process, and made a further break with tradition by creating a new Christian capital, inaugurated in 330: ‘New Rome’ (later called ‘Constantinople’) on the Bosphorus. The idea of a permanent Imperial capital in the East for a locally resident Emperor had been Diocletian’s, but he had chosen the established Bithynian city of Nicomedia. Constantine set up a much more radical project, with a new and carefully planned city (based on a previous, smaller Greek town) with the facilities that were to become appropriate for medieval Christian cities (e.g. a cathedral). He also set up a Senate and encouraged aristocratic families to move to the city, going further than his predecessors had done; the new capital was clearly meant to supersede the old one.
It was also linked to a huge and dominant court and a regular round of Imperial ritual that added mystique to the Imperial office, though the unique and non-Roman nature of this may owe more to hindsight, as Constantinople was the only Late Roman capital to survive for centuries. Constantine still kept the senior role of Western Emperor for his eldest sons, Crispus (killed 326) and then Constantine II, who were based at Trier. The literary evidence certainly hints at him having a form of megalomania in his later years, which may have influenced the boldness and grandiosity of his plans. His family life ended up replaying ancient Greek myth, as he killed Crispus at the behest of the latter’s stepmother Fausta and then killed her for false accusations, an echo of Theseus, Hippolytus, and Phaedra.
Augustus had laid claim to the loyalty of the troops of his late greatuncle’s armies from 44 BC as his genetic heir, the new Caesar, and duly outmanoeuvred the more experienced senior general Antony. The new system focussed loyalty on the ‘Princeps’ in his role as ‘Caesar’, with a family surname turning into an administrative title, and the hereditary basis of power was established. Significantly, the ailing Augustus’ designated heir in 23BC was his young and untried genetic heir, nephew and son-in-law Marcellus, not an experienced political and military lieutenant like Agrippa; in later years the choice fell on his equally inexperienced grandsons. The unique position he had created for himself became a hereditary monarchy, though with the technical caveat of confirmation of powers by the Senate. When the latter attempted to choose their own (or no) candidate for ruler after Caligula’s murder in January AD41 they were swiftly reined in by the Praetorian Guard.
Augustus eventually attempted to lay down a form of succession by the most experienced member of the Imperial family rather than by father-son descent, arranging for his stepson Tiberius to be followed by Tiberius’ older, militarily senior nephew Germanicus, who was married to Augustus’ own grand-daughter, not by Tiberius’ son Drusus. Drusus (maybe two years younger than Germanicus) would then be followed by Germanicus’ sons. Tiberius kept to this faithfully, and put Germanicus’ sons ahead of Drusus’ (under-age) son Tiberius Gemellus in the queue to be Emperor. Arguably, Claudius did the same in putting his stepson Nero ahead of his own, younger son Britannicus. This system then evolved to father-son descent in the second century, when an Emperor had a son or brother, which was not the case from 81 to 161.
But a wholly hereditary system of rule, whereby the next eligible adult male (son, brother, or cousin) inherits irrespective of capability, introduces the risk of incompetence or insanity. This is followed by the overthrow of the incumbent by a more competent but illegitimate successor, who can then be challenged by ambitious relatives or military commanders. One coup leads to another, a minority is the inevitable opportunity for adults to overthrow the under-age sovereign, and prolonged instability is only ended by a strong ruler. This is what happened to the English monarchy in 1399, 1461, 1470–1, and 1483–5, though other kingdoms (such as France in 987–1328) had a luckier run of unchallenged capable heirs (usually adult) in direct succession.
If a state dominated by its officer-corps or provincial generals turns into a hereditary monarchy, any succession of an inexperienced minor can lead to coups by the military, as seen by the repeated fate of Sultans’ under-age heirs in Mameluke Egypt after 1260. This fate happened to Gordianus III of Rome, teenage ruler in 238–44, at the hands of his Praetorian Praefect Philip. If there is an heir entrusted with a governorship and army outside the capital, they can then overthrow their sovereign, as Julian did to Constantius II in 360–1, and as occasional Ottoman Sultans did, e.g. Selim I to Bayezid II in 1512. If a state is split among a multiplicity of eligible adult heirs as corulers, mutual assistance is less likely than endless struggles for supreme power, of which invaders then take advantage, as with Carolingian Francia among Louis the Pious’ sons in the 840s. If the state is lucky, one heir can quickly destroy his rivals and reassert central authority, as Bayezid II and Selim I did in the Ottoman civil wars of 1481 and 1512. If it is not, a standoff and permanent division ensues as in Francia post-843.
In Rome’s case, the split of power among multiple heirs in the fourth century often led to civil wars among the rivals which only ended with one candidate’s victory, as after Diocletian’s abdication in 305 and Constantine’s death in 337. The division between Valentinian and Valens in 364 was better managed. It was not fatal to a militarily strong Empire, despite the loss of manpower in internecine warfare; but after the split of 395 the mutual mistrust of Arcadius’ East and Honorius’ West was to give Alaric’s Gothic armies a crucial opportunity to play one Emperor against the other and militarily overshadow both.
In the case of Rome’s principal contemporary equal, Han China and its heirs, a succession of weak rulers in thrall to a feuding court bureaucracy and the repeated accession of minors led to instability and decline at the centre of power and ultimately to successful military challenge from the provinces. Once a regular succession of competent adults to the throne failed, central power weakened and the Emperors became puppets of their ministers, as with several initially successful Chinese dynasties after the Han, most notably the T’ang in the ninth century. In Japan, the powerful court dynasties surrounding the throne in the ninth century and afterwards even kept the throne restricted to under-age rulers in order to secure a succession of lucrative regencies. In Sassanid Persia from 226, a more centralised state with a more unified army than that of its Parthian predecessor, a long-lasting dynasty survived under rulers of varying merits with only a few internal non-dynastic coups, e.g. in 590. This was probably due to the overwhelming power of the central as opposed to provincial armies, which coup-prone Parthia had lacked.
No provincial warlord would think it worth challenging a State with overwhelming military superiority. That factor probably kept most ambitious Roman provincial commanders from challenging the Emperor in Rome until the rule of Nero deteriorated and made the central authorities vulnerable in 68. Once there was a hiatus in Rome or one commander dared to rebel, it was open season for would-be rebels to join in, as in AD69, 193, and 260.
The reliance of the Roman political system on the merits of one man, as introduced by Augustus, had ended earlier instability. The repeated politico-military struggles and usurpations of the period from the Gracchi to Actium had been caused primarily by the feuding over power of the rival senior noble families and ambitious new men of the late Republican patriciate, and centred on the senior provincial governors’ possession of armies. Ultimately, with Julius Caesar and then Octavian-Augustus, only one political leader was left with full control of all the Republic’s armies, and the latter, as ‘Princeps’, ensured that the armies remained loyal to him and his family and that the political system was unobtrusively turned into a monarchy while remaining technically a republic. Unlike Caesar, he did not flout the cherished ‘mos maiorum’ and he enabled the Senatorial aristocracy to live within the fiction that the traditional constitution was being maintained, once he had slaughtered all real or potential serious challengers.
The succession problems of his dynasty are well known, and were survived by luck as much as by good judgement in the case of two mentally unstable rulers (Caius ‘Caligula’ and Nero) who were murdered and one civil war (AD69). Luck could have been better and there have been no tyranny, for example if Tiberius had been succeeded by his original heirs, but his nephew Germanicus, his son the younger Drusus, and the former’s son Nero Caesar all predeceased him, possibly violently. Caligula was only Germanicus’ third son and was an unlikely successor until the destruction of his elder brothers, Nero by the jealous Sejanus and Drusus (II) by Tiberius for betraying his family to Sejanus. Nor did Caligula’s worst traits become apparent until after a serious illness months after he succeeded Tiberius in 37; did this illness emotionally unbalance him?
Britannicus was only in his early teens when Claudius died, and the latter had political reasons for advancing his older stepbrother Nero as senior heir. Nero was more closely descended from Augustus and his mother’s family were popular with the troops. Possibly Claudius even suspected that Britannicus’ nymphomaniac mother Messalina had used one of her lovers to father the boy, or that his enemies, led by Nero’s mother Agrippina, would say that. But an older and more viable Britannicus could have succeeded his father as an adult around 60–62. Claudius might not have adopted his stepson Nero as senior heir, or Claudius discovered Agrippina’s poison plot in time in October 54. The Julio-Claudian succession system would have worked then and not have seemed inferior to that of the Antonines in retrospect. The Empire would not have had to wait to 96–180 for a run of good Emperors.
Thereafter the Roman Empire had been lucky in its transmission of the succession from 96 to 180, no ruler except Marcus Aurelius having an adult close relative to succeed him. But the succession was not always smooth, as with the mysterious political executions of four consuls early in Hadrian’s reign and the early death of his chosen heir Aelius Verus. It was unlucky thereafter. There was not a conscious system of choosing the best man as Edward Gibbon and other historians believed; if an Emperor had a son of whatever age or quality, as Marcus with Commodus, the choice of heir was clear, and the army would probably have baulked at accepting any substitute. Marcus would have had problems had he proposed to set his incompetent son Commodus aside, assuming that the latter’s faults were already visible by the time of Marcus’ death; the most blatant acts of Commodus’ misrule occurred after some years in power. The new Emperor (aged nineteen) was taken advantage of by flattering Court favourites such as Saoterus and later Cleander, a perennial problem for a vain and impressionable young autocrat (as shown by the initially good Nero). For that matter, it should be remembered that Commodus had a twin and a younger brother, both of whom died young; had either of them replaced him on his murder in December 192 there would not have been a succession crisis and civil war then either. Instead the chosen new ruler, the competent but brusque and disciplinarian general Pertinax, alienated the over-indulged Praetorian Guard and was soon murdered too.
The run of poor or easily challenged rulers in the third century was not inevitable, and some Emperors ducked their responsibility to provide an adequate and unchallenged heir, most crucially Septimius Severus with Caracalla and Geta in 211. It should also be remarked that the Empire had been lucky in that a new civil war did not erupt in 97–8 after the unexpected extinction of the Flavian dynasty. The shaky regime of the elderly, obscure, and heirless Nerva, defied by its own guardsmen, swiftly adopted a powerful and charismatic military commander (Trajan) as its heir to ward off another civil war. Nerva was fortunate to avoid the fate of the similarly placed Galba thirty years earlier. There was no certainty in 193 that Pertinax would not be able to control the Guard, or that he would be killed rather than just defied as Nerva had been in 97. Had he been more careful or tactful, this veteran commander (aged sixty-six in 192/3) could have averted murder and civil war and passed on the throne to his chosen heir, either Septimius Severus, an earlier protégé, or the latter’s rival Clodius Albinus. Instead, the son-less second and third century Emperors sought to bolster legitimacy by adopting their heirs, which was bizarre at times, as when Elagabalus adopted his cousin Alexander Severus, four years younger than him. Septimius Severus retrospectively had himself adopted posthumously by Pertinax.
The habit of provincial military challenges to the centre of power had been a threat to the Roman polity ever since the emergence of powerful provincial armies. Sulla had used his armies in Greece to overthrow the regime of Marius’ heirs in 83–2BC, Caesar had marched on Rome from Gaul in 49BC, and in 43 the Senate was helpless before the triple alliance of Antony, Octavian, and Lepidus. It recurred throughout the early Empire at times of crisis and uncertain leadership in Rome, potentially (though aborted) with Gaetulicus in AD39 and Scribonianus in 42 and fully with the civil war of 69. Augustus, lucky in the possession of a large family, had where possible kept the armies in his loyal and competent male relatives’ hands. It resumed with the instability following Pertinax’s murder in 193 (though there was an abortive revolt as early as the rumours of Marcus’ death in 175), and became endemic after 235. But once the chances of a revolt succeeding had become greater, with the lack of an recognisably dominating ruler and stable dynasty in Rome, the temptation to challenge the Emperor became greater. One successful revolt bred another, and in turn the preoccupation of the current incumbent with survival meant that external enemies were emboldened.
The safest military solution to this was that adopted by the late Roman state, probably through a deliberate plan by Diocletian which Constantine reinforced; the central army at the Emperor’s disposal, the ‘comitatus’, outnumbered any provincial army and the old Augustan provinces were split into many smaller ones so that no provincial commander had enough men to risk challenging the government. Each province also now had a separate civil and military governor. This did not stop some bold commanders, as with Maximus in Britain in 383, a desperate man like Silvanus in Trier in 355, or a junior Imperial prince commanding a ‘comitatus’ on a threatened frontier, as with Julian in Gaul in 360; but it made revolt more risky and so halted the epidemic of risings in the 250s and 260s.
In the 250s the instability at the centre, coherent military challenge from Persia, and opportunistic attacks from Germanic tribal coalitions across the Rhine and Danube – all feeding off each other – came together at a time when the Empire’s manpower was being undermined by plague. The results were catastrophic. But what if there had been greater political stability within the Empire at this juncture?
The 250s and after: dynastic mischance and its exploitation
Apart from the military advantages of a firm and continuing response to outside threats, greater political stability from a secure succession process would have enabled the Empire to call upon its full revenues for and troops from all unaffected provinces to aid the government and military. The plague of 252 would still have diminished both, making the chances of defeat and a civil war higher, particularly with the opportunistic Persian Great King Shapur I ready to invade. The defeat of the Eastern armies, sack of Antioch, local power-vacuum, and seizure of the politico-military initiative by Odenathus and Zenobia of Palmyra in the 260s were probable if the Rhine or Danube wars had tied down the Western armies. If the Emperor marched East and had no capable colleague to guard the threatened Rhine, a revolt on the latter was probable. In real life the local commander Postumus deposed Gallienus’ young son and set up a breakaway Gallic-Spanish-British realm in 260 and it was not reconquered until Aurelian had dealt with Palmyra in 272–3.
Recovery should have been quicker without the multiplicity of revolts in 259–67, and the strain on resources to pay for the enlarged Diocletianic army and civil service less without the economic dislocation caused by ravaging across many provinces. The efforts usually attributed to a bureaucratically minded Diocletian to secure adequate manpower for vital professions (the military and agriculture in particular) centred on the solution of making them hereditary, while economic problems were tackled by similar legislation. Inflation was solved by being banned, the reaction of a despot like a modern Third World dictator. Diocletian’s crucial lack of a male heir led to an ingenious attempt to solve the endemic problem of the succession by another administrative solution. The two new Emperors, of East and West, would each adopt a competent adult heir who would serve as deputy ruler or ‘Caesar’ under him before succeeding to the throne. Was this only suggested because Diocletian had no son? This idea was unworkable given human nature and the desire of the men involved to pass on their power within their families, and it was duly wrecked by a complicated power struggle among Diocletian’s heirs after he retired in 305.
The outcome was the personal ascendancy of Constantine as sole ruler in 324, followed by his own attempt to divide up the Empire among his sons and nephews, which also collapsed in bloodshed in 337. The successive bouts of political instability and civil wars which followed saw no dynasty surviving with stable adult male rule for more than a few decades, although the loss of manpower in civil war did not immediately affect the Empire’s survival when it lacked external challengers. But indirectly the effects of dynastic strife commenced the process of political disintegration; Valentinian I’s unwise choice of his brother Valens as his co-ruler in 364, criticised at the time, presented the East with the man who mishandled the Gothic crisis of 376–8 and was killed in Rome’s first serious military defeat at German hands since the 250s. After the death of Valens and destruction of the Eastern army at Adrianople in 378 the Goths, initially a flood of refugees from Hunnic incursions into their steppe homeland not a hostile invading army, were able to maintain their own polity within the borders of the Empire. Nominal military vassals at first, after their accommodation with Theodosius in 381, their Gothic-commanded forces were outside the Roman chain of command, and were able to exploit the vacuum in leadership that followed Theodosius’ death in 395.
At this point, the Empire’s physical loss of control of the provinces, and their manpower and revenues, commenced, and the Germanic warlords within its borders began to be a serious military challenge. The spiral of Decline and Fall, began, more specifically meaning a growing loss of resources and military power in the West at a time of rising challenges from unchecked Germanic warlords who could not be intimidated or bought off indefinitely. There has been much argument over the size of the barbarian hordes, the amount of damage and economic dislocation, and the possible exaggeration of their depredations. But the loss of Imperial political control of the outlying provinces, leaving a rump state at the mercy of its German-led armies in the 460s, speaks for itself.