In 31 BC in the aftermath of Actium, Octavian held under his control not only the combined legions of his own and Antony’s armies, totaling some 60 legions of probably varying strength, but also the fleet that had won his decisive victory for him, numbering some 400 or so ships, and the unrecorded numbers of allied units that had contributed to the armies of the triumviral period. These numbers needed to be reduced: an over-large army was financially unsustainable, would be impossible to employ usefully, and posed a threat to political and social stability. Romans saw the existence of large armies loyal to individual generals rather than the state as a major factor contributing to the civil strife of the late republic; they were also clear evidence of political crisis (Cassius Dio 52.27).
If Augustus wanted to stabilize the state and build public confidence in his new regime, he needed to show that the crisis was over. A massive reduction in the legions would help to do this, as well as appease the soldiers themselves, many of whom had enlisted or been conscripted to fight for individuals in civil war and were eager to be discharged with an appropriate reward. Whether reducing the size of the army would have provided any reassurance to the Senate as to the nature of Augustus’ regime is another matter, but the princeps himself considered it important enough to give it considerable prominence in his Res Gestae. The inscription begins with an extremely brief and partisan account of Augustus’ rise to power, a bald statement concerning the extent of his campaigns and conquests, and then, the first action of the newly self-appointed princeps to be recorded is that of the half a million men under arms he discharged 300,000 of them with the reward of land grants or cash bonuses (Res Gestae 3).
In order to retain his position as Rome’s sole leader and prevent a recurrence of the civil wars and political instability that had brought an end to the republic, Augustus needed not only to maintain firm control of the army, but to change its whole relationship with the Roman state. The military reforms he undertook served to remove soldiers from the active involvement in politics that they had enjoyed during the last century of the republic and the triumviral period, and aimed to break the ties of loyalty to individual generals and expectation of reward that had made a major contribution to the end of the republic; instead the army’s loyalties were directed towards the emperor and members of the imperial family rather than to their own commanders.
The citizen militia of the early and middle republic was already evolving into a more professional army by 31 BC, but Augustus accelerated that process by establishing a standing army with permanent units of citizen legions and noncitizen auxiliaries. The army was based in the provinces and on the frontiers; with the exception of the Urban Cohorts and Praetorian Guard, no military units were stationed in Italy, which had suffered so much during the wars of the first century BC, and Italian society swiftly became demilitarized. Whilst many of Augustus’ military “reforms” were little more than the regularization of changes that had been taking place in the late republic, others were radical in the context of a generally conservative society that placed great emphasis on ancestral traditions.
By the late republic the legions, which had originally been raised on an annual basis to wage war in Italy, were serving for continuous periods, sometimes for many years, in provinces throughout the Mediterranean. That length of service could vary enormously. The two legions raised by Valerius Flaccus in 86 BC for the campaign against Mithridates were still serving when Pompey took over the command nearly 20 years later, whilst the three legions of Metellus Creticus involved in operations against pirates may have served for only three years, from 68-65 before being returned to Italy and discharged.
The rewards of service could be equally inconsistent with some legions being settled on land, such as Saturninus’ settlement of Marius’ veterans (Appian, B. Civ. 1.29) and Sulla’s displacement of Italian farmers to settle his civil war veterans, whilst other legions received no substantial reward when their service was completed. The potential reward on discharge was one of the principal factors that encouraged the loyalty of soldiers to their generals rather than to the Roman state, and contributed to the civil wars that ended the republic. By establishing fixed rewards which were available only after completion of an established minimum length of service, Augustus was able to break the financial dependence of soldiers on their generals and some of the ties of loyalty.
This might seem an obvious solution, and, after the establishment of the aerarium militare in AD 6 to finance the settlement of veterans, an appropriate one since the new taxes inevitably had a greater effect on the elite who had so steadfastly refused to reward veterans in the late republic, but we should not be too critical of the senate for failing to take such steps earlier. In spite of the growing tendency in the last century of the republic for some citizens to see the army as a profession and the decreasing importance of any kind of property qualification for legionary service, there had remained a strong belief in the idea of a Rome whose military superiority lay in the traditions of a citizen militia drawn on the property owning classes who served in the legions when necessity demanded. The creation of an army of long-service professionals recruited regardless of social, and sometimes citizen, status signaled an end to this central feature of the Roman Republic, and even though it was merely the next logical step in the evolution of the Roman army, Augustus drew on republican precedents in establishing his imperial army.
After the mass settlement of veterans following Actium, Augustus retained in service 28 of the legions that had been in existence in 31 BC, drawn from both his own and Antony’s armies. Although the number of legions fluctuated over the next two and a half centuries as units were destroyed, disbanded for dishonorable behavior or raised for campaigns, the total number of legions, and indeed overall size of the army, did not change fundamentally from that established by Augustus, as indicated by Cassius Dio’s valuable summary of legionary comings and goings (Cassius Dio 55.23-24). Tacitus (Ann. 4.5) stated that the number of auxiliaries approximately equaled that of the legionaries, but opted not to provide a list of all the units and their stations because there were so many; military strength in the early imperial period was around 300,000, about half of whom were legionaries and half auxiliaries.
In setting the length of legionary service, Augustus drew on the traditional requirement that a citizen be available for up to 16 campaigns, or 20 in times of national emergency (Polybius 6.19) and set service at 16 years plus four in reserve. Dio records this in 13 BC (Cassius Dio 54.25), but it is likely that since Actium there had been an expectation that soldiers would serve for this length of time. In AD 5, this was increased to 20 plus five in reserve; whatever the distinction was between ordinary soldiers and those in reserve, it seems to have been dropped fairly soon afterwards and all legionaries and auxiliaries served for 25 years. Conscription through the dilectus remained an option but although there are occasional references to levies, such as during the Pannonian revolt or in the aftermath of the Varian disaster, or the occasional levy of non-citizen troops in the provinces, the vast majority of recruits were volunteers.
Augustus did not raise military pay which had been doubled to 225 denarii a year by Caesar (Suetonius, Jul. 26), but soldiers were now guaranteed a regular income for a fixed period of time, followed by a guaranteed discharge bonus. At first the reward for veterans came in the form of a land grant, following the precedents of the late republic and triumviral periods, and continuing, though in a different form, the long established link between land ownership and military service. Augustus went to great efforts to avoid the confiscations that had provided for veteran settlement in the unsettled decades at the end of the republic. Such redistributions of land were associated with civil strife and political dominance such as Sulla’s dictatorship or the triumvirate, in which the then Octavian had been responsible for the deeply unpopular confiscations in Italy following Philippi (Appian, B. Civ. 5.19; Suetonius, Aug. 13; Vergilius, Ecl.).
As Augustus, he ensured that in both Italy and the provinces the lands assigned to the veterans were purchased, not confiscated, and he publicized in his Res Gestae not only the extraordinarily large sums he personally committed to this task (a total of 860,000,000 sesterces for the large-scale settlements of 30 and 14 BC), but also the boast that he was the first and only person to have paid for such lands, another clear sign that the political and military crises of the late republic had been resolved. The size of the allotments is not known, though it is estimated that they may have been up to 50 iugera (14.7 ha) for ordinary legionaries, sufficient to provide for a family and produce a surplus, and more for former centurions and tribunes.
Military colonies were set up throughout the empire, and 28 were established in Italy (Res Gestae 28). However, Augustus was unable to sustain this kind of expenditure and there was a limit to the amount of available land, especially in Italy, so increasingly the discharge bonus was paid in cash rather than land. These pay-outs, recorded in the Res Gestae, amounted to 400,000,000 sesterces and were made in 7, 6, 4, 3, and 2 BC (Res Gestae 16). The soldiers receiving these cash bonuses on retirement had been recruited in the 20s BC, had not fought in civil wars, and had only ever sworn an oath of allegiance to Augustus, who was by now so well established in power that he could afford to divert from republican traditions, and perhaps be less generous to his soldiers.
The evidence of the Res Gestae suggests that by the end of the first century BC a cash bonus on discharge had become the norm, and this is confirmed by Cassius Dio who records that at the same time that military service was increased to 25 years in AD 5, the bonus was set at 12,000 sesterces, a sum equivalent to over 13 years’ pay. To finance the retirement benefits of 4,000-5,000 men a year, Augustus established the aerarium militare, the military treasury, in AD 6, which he set up with a donation of 170,000,000 sesterces from his own funds (Res Gestae 17). The treasury’s income was derived from the introduction of new taxes, a 1 percent tax on sales at auction and a 5 percent inheritance tax. Whether auxiliaries also received such retirement payments is uncertain, but probably unlikely; from the time of Claudius, however, they automatically received Roman citizenship after their 25 years’ service. With the establishment of fixed lengths of service and retirement benefits, and a dedicated treasury to finance the latter, it is apparent that by the beginning of the first century AD, the Roman army was now a professional force; whereas in the republic the ideal was of the citizen soldier, now Augustus even separated his soldiers from the ordinary people in the theater (Suetonius, Aug. 44).
Augustus ensured the loyalty of his new professional army through these financial arrangements, and through other means. The sacramentum or oath of allegiance, had originally been sworn by legionaries who undertook to obey the consuls or their generals for the course of the campaign, and generals in the late republic had drawn on this to encourage great loyalty from their armies as the oath was sworn to them personally (Plutarch, Sulla 27); Augustus took this one stage further by requiring all those under arms to swear allegiance to him personally, rather than to their unit commanders or provincial governors, and this was repeated annually (Tacitus, Hist. 1.55).
At some point in the early empire, the imago was adopted as an additional military standard by both legions and auxiliary units; this standard was one which carried the image of the emperor (who also appeared on the coinage in which they were paid) and served to identify the unit with their emperor and commander in chief; the imago was closely associated with the unit’s standards which were considered sacred and housed in a sacellum in the principia or headquarters building when the unit was in garrison. The Rhine legions first expressed their change of allegiance from Galba to their provincial governor Vitellius by stoning or destroying the imagines of Galba (Tacitus, Hist. 1.55).
Various legal advantages were bestowed on soldiers, though to facilitate the swift movement of troops and their separation from civilian life, they were forbidden to contract legal marriages, another factor highlighting the difference between the republican army and the professional army of the principate.
The commanders and senior officers of all military units owed their positions to the patronage of the emperor, though it is uncertain whether or not centurions were also appointed directly by the emperor. Officers of senatorial and equestrian status owed future career promotions and magistracies to the emperor’s patronage whilst centurions were probably encouraged in their loyalty by rates of pay that were vastly superior to those of ordinary legionaries, and by the status and future career opportunities in imperial service that the most senior centurions could attain.
The loyalty of tribunes, prefects, and legates could contribute to the loyalty of those under their command, but ordinary soldiers were very aware of their own oaths of allegiance; there were no serious military threats to Augustus’ power and given the chaotic last decades of the republic and almost constant civil war, he did a remarkable job of taking firm control of Rome’s armies and establishing the armed forces that would maintain the pax Romana for several centuries.