The Later Roman Empire

Even more pressing than the question of military security was that of how to put an end to the rapid turnover of emperors. Diocletian’s answer lay in the establishment in AD 293 of a system of power-sharing known as the tetrarchy (rule of four), by which there would be two Augusti and two Caesars, the latter destined in due course to succeed. Once established, the tetrarchic system lasted until it was destroyed by the ambition of Constantine, who had been raised himself on the death in AD 306 of his father, Constantius, who had first been made Caesar and then Augustus during the reign of Diocletian. Diocletian’s scheme did not come into being immediately on his accession. His first step was to raise another Illyrian soldier, Maximian, to the post of Caesar, at the same time adopting him as his son, though he was only a few years younger than himself (AD 285). An ad hoc division of responsibility gave Maximian the west while Diocletian was in the east; the fact that a certain Carausius had been declared Augustus in Britain no doubt influenced Diocletian to make Maximian Augustus in AD 286. Even then, the further step of appointing two Caesars was not taken until March, AD 293. Constantius and Galerius now became Caesars to Maximian and Diocletian respectively; the arrangements were sealed by dynastic marriages and the adoption of Diocletian’s family name Valerius, and advertised on coins and in official panegyric. Diocletian and Maximian, meeting formally at Milan in the winter of AD 290–1, had already affiliated themselves to the gods Jupiter and Hercules by taking the divine titles Jovius and Herculius, and their Caesars shared the same titulature and the same religious associations. As heir to his father Constantius, Constantine too is attested as Herculius in AD 307.

A porphyry statue group now to be seen as part of San Marco, Venice, shows the tetrarchs as squat figures in military dress, embracing each other. The surviving Latin panegyrics, like the Historia Augusta, emphasize unity and concord:

Four rulers of the world they were indeed, brave, wise, kind, generous, respectful to the senate, friends of the people, moderate, revered, devoted, pious. (SHA Vita Cari 18)

Such heavy-handed propaganda betrays the fragility of the new arrangement: it rested on nothing more solid than consent. Carausius, who had seized power in Britain, was murdered and replaced by his rival Allectus in AD 293; Allectus was defeated in turn by Constantius in AD 296, who then entered London as a liberator (Pan.Lat. 8(5)). Not that the defeat rewarded legality at the expense of usurpation, as the victors naturally claimed, for Carausius had been recognized as Augustus in Britain and north-west Gaul, and had issued coins in that capacity.

The propaganda, and the religious aura claimed for the tetrarchy, no doubt helped to impress their subjects, and to reassure Diocletian and his colleagues themselves, but it was in fact military, and by extension political, success which conferred legitimacy. Diocletian’s system remained in place only until it was challenged from within, after Diocletian himself retired in AD 305. Luckily for the empire, however, even though the tetrarchy was threatened in its early years by the regime of Carausius, it did ultimately succeed in providing a period of stability lasting nearly twenty years – long enough for some far-reaching changes to be introduced.

Any assessment of the nature of Diocletian’s reforms is rendered difficult by two factors: the unsatisfactory nature of the surviving literary evidence for his reign, and the fact that many individual changes either came in at a later stage, or are only attested later. Another problem is caused by the exaggerated contrast between Diocletian and Constantine which prevails in the sources; rather, Constantine’s secular policies, and even some aspects of his religious ones, should be seen as continuing the general line established by Diocletian.

One of Diocletian’s first priorities was military: not only had the army to be brought under central control and made into a force capable of defending the security of the empire, but it also had to be reliably supplied. The literary sources attribute to Diocletian the most fundamental changes that the Roman military system had experienced since the days of Augustus, and they have been followed by most modern scholars; however, it may be doubted whether the break with what had gone before was quite as sharp as this suggests. The way had already been prepared by earlier emperors, including Marcus Aurelius, Septimius Severus (AD 193–211) and Caracalla (AD 211–17). During their reigns army pay was doubled, donatives to the soldiers institutionalised, the army itself enlarged and openings for military men in the administration greatly increased. More units had certainly also been raised in the course of the third century. The hostile Lactantius associates the reforms of Diocletian with his establishment of the tetrarchy:

he appointed three men to share his rule, dividing the world into four parts and multiplying the armies, as each of the four strove to have a far larger number of troops than any previous emperors had had when they were governing the state alone. (DMP 7.2)

But Lactantius can hardly be taken to mean that the army had quadrupled, especially as it is likely that it had already risen during the third century to something over 350,000. More probably this, like other remarks in the same chapter, is a hostile exaggeration, more a jibe than a sober estimate. Diocletian did perhaps increase numbers (new units were certainly created), but may not have done very much more in general than recognize and regularize the status quo. The backbone of the army had traditionally been the legions, well-armed and well-drilled units of about five thousand infantry. Reading back from the evidence of the Notitia Dignitatum (see above, Chapter II), Diocletian created new legions on a considerable scale, giving them names such as Iovia, Herculia, Diocletiana and Maximiana, while others had already come into being during the third century. But a large increase in the number of legions does not necessarily imply a doubling of the actual numbers of troops. Archaeological evidence drawn from the size of legionary fortresses and literary evidence both show that legions in the later Roman empire were much smaller than their predecessors, typically comprising only a thousand or so men, while special detachments (vexillationes) often stood at only five hundred or less; this implies that the calculations of total size based on earlier norms will be very misleading, and suggests that the actual total was considerably less than is often supposed.

Calculating the size of the late Roman army is very difficult. We have few actual figures for its total. At least one of them (six hundred and forty-five thousand, according to the historian Agathias, writing in Constantinople in the later sixth century) is impossibly high, although it might reflect a paper figure never realized in practice. Calculations based on the figures in the Notitia are likely to suffer from similar limitations. It ought to be possible in theory to base overall calculations on papyrus evidence surviving from AD 299–300, which gives the levels of pay for certain regiments, but here too there are many imponderables as to the actual size of the units. Yet the total size of Diocletian’s army is extremely important in assessing the economic problems which may have led to later decline, for if it really did double in size, the extra burden on the state revenues would indeed have been colossal. Current research seems however to point to an army size of not much more than four hundred thousand; even so, the implications for supply, pay and recruitment were extremely serious (for further discussion, see Chapter IX below).

Like Lactantius, the pagan historian Zosimus draws an exaggerated distinction between Diocletian and Constantine when he accuses Constantine of having damaged Roman frontier defences by removing ‘most’ of the troops from the frontiers, where they had been placed by Diocletian, in order to create a new field army (New History II.34). He adds that these soldiers thus became accustomed to the luxury of life in cities, and grew enervated as a result. But this is all part of his tirade against Constantine; we know from epigraphic evidence that the field army (comitatus) certainly already existed under Diocletian and indeed earlier (Constantine may simply have enlarged it), while the stationing of soldiers in or near cities was a direct function of the problems of army supply and requisitions. All agree that Diocletian strengthened the frontiers, building forts, strengthening natural barriers and establishing military roads from Britain in the west to the so-called Strata Diocletiana in the east, a road running from the Red Sea to Dura on the Euphrates. But it is unlikely that these borders were yet manned by limitanei, farmer-soldiers living on the frontiers, who emerge only later. Moreover, the policy of ‘defence-in-depth’ attributed to Diocletian and popularized in a book by the modern strategist Edward Luttwak and others, whereby the border troops were designed to hold up invaders until crack troops moved up from defensive positions further inside the empire, has been deservedly criticized by archaeologists and others who have studied the material remains in detail (see Chapter IX). The Roman army in the late empire was different from that of Augustus, and used in different ways. Ammianus gives a vivid picture of the varied and sometimes outlandish insignia in use in the second half of the fourth century. In the same period recruitment in some areas became difficult and unpopular; the place of volunteers was therefore taken more and more by conscripts and by barbarians, both as regular troops and as federate mercenaries. But like much else this took time to work through, and we should not attribute more to Diocletian than he actually did.

One of the most severe problems associated with the army was that of pay and supply. With the collapse of the silver coinage, used for the payment of taxes and the soldiers’ wages, the army had to be paid and supplied partly in requisitions in kind through the annona militaris and the capitus (a fodder ration). If such a system worked at all, it was bound to be unreliable, clumsy and extremely burdensome on local populations, who never knew what was going to be demanded from them or when. Since perishable goods could not be carried far because of the extreme slowness of land transport, there were also formidable problems of supply. It is a miracle that some level of central organization was nevertheless maintained in such conditions; however, some improvement had to be sought. Diocletian effectively recognized the status quo and introduced an elaborate new tax system in kind, based both on capita (‘heads’, i.e. poll tax, capitatio) and land (iugatio). All agricultural land was divided into notional units known as iuga, varying in size according to the assessment of their productivity. Iuga, tax units, are not to be confused with iugera, units of area; thus in Syria, five iugera of vineyard made one iugum, which might however comprise as much as forty iugera if the land were of poor quality. Mountain territory was specially assessed on a local scale of productivity; a later legal textbook describes the process:

at the time of the assessment there were certain men who were given the authority by the government; they summoned the other mountain dwellers from other regions and bade them assess how much land, by their estimate, produces a modius of wheat or barley in the mountains. In this way they also assessed unsown land, the pasture land for cattle, as to how much tax it should yield to the fisc. (Syro-Roman Law Book, cxxi, FIRA II.796 = Lewis and Reinhold, II. 128)

Not only that: what was actually to be paid also ideally had to be linked to what was produced locally. The whole was to be assessed by a regular census, organized by five-year periods, known as indictions, from AD 287 onwards.

By these means, Diocletian sought to establish for the empire something like a regular budget, and some check was placed on the ad hoc requisitions which had become such a burden during the third century. The system aimed at providing what the troops needed on a regular and reliable basis. A. H. M. Jones comments that its great virtue lay in its simplicity (LRE, I, 65). This however is a modern view; in the conditions of the late third century, the amount of work and organization needed to put it into practice was beyond all proportion to what had gone before, and the mechanisms of economic control were both crude and poorly understood. In practice there was considerable variety from province to province, and while a large amount of evidence survives to show how the reforms were carried out, it is very unevenly distributed. Thus we know something of what happened in some areas – Syria and Egypt, for example – but nothing at all about others, such as Spain or Britain. It is therefore impossible to judge how effective the system was in any detailed way, though we can assume that Diocletian’s arrangements remained in force. But cash payments also remained in force for the army, as can be seen from the ample evidence of minting of coin, and the annona itself often took the form of compulsory purchase of goods by the state rather than transactions wholly in kind.

These were reforms of practice, not of principle: the major tax burden continued to fall on those least able to bear it, the main tax still fell on the land, and the notion that high status should carry with it exemption from certain taxes was an idea which permeated Roman attitudes to taxation at all periods, even when the empire could least afford it. Diocletian did not attempt to introduce taxation of senators or merchants, and when Constantine did so the initiative was highly unpopular. Whether the overall rate of taxation was itself actually substantially increased, as has been argued in the past, is doubtful; indeed, papyrological evidence suggests that it remained surprisingly stable over many centuries, from the early empire to the beginning of the Byzantine period in Egypt. This means that the net effect of Diocletian’s innovations was much less dramatic than is often supposed. Without technological innovations there was a natural limit to productivity, even had there been no adverse factors such as population drop or damage from war and invasion. Nevertheless, the new system of assessment may have helped to ensure a higher rate of recovery of notional tax revenue, and to that extent will have been helpful to the state (and unpopular); it probably also increased, if only temporarily, the ratio of tax receipts in kind over taxes collected in cash.

But there were other problems to face, including continued inflation and a shortage of gold and silver in the treasury, which Diocletian and Constantine attempted to address by requiring the rich to commute precious metal for bronze. Matters were not helped however by the large-scale minting of bronze, or rather base-metal, coins (the bronze content was minimal) by the government in response to the collapse of the silver denarius, now a paper unit only; prices continued to spiral throughout Constantine’s reign as well as Diocletian’s. The latter’s most famous measure in the monetary sphere was his attempt to prescribe maximum prices by imperial decree (‘Price Edict’, or Edictum de maximis pretiis, AD 301). With its minute attention to detail, Diocletian’s edict provides us with our largest single source of information on the prices of ordinary goods. It could not succeed however in the absence both of an adequate mechanism for enforcement and of parallel regulation of supply. The disproportionate penalties it lays down conceal the fact that the means of enforcement simply did not exist. Hostile critics like Lactantius gloated when it was soon withdrawn:

this same Diocletian with his insatiable greed was never willing that his treasuries should be depleted but was always measuring surplus wealth and funds for largess so that he could keep whatever he was storing complete and inviolate. Since, too, by his various misdeeds he was causing prices to rise to an extraordinary height, he tried to fix by law the prices of goods put up for sale. Much blood was then shed over small and cheap items, and in the general alarm nothing would appear for sale; then the rise in prices got much worse until, after many had met their deaths, sheer necessity led to the repeal of the law. (DMP 7.5–7)

Diocletian’s attempt at price control was accompanied by equally unsuccessful measures to reform the coinage. Both failed because they were imposed from above without sufficient understanding or control of the general conditions which were in fact causing the difficulties. Lactantius uses a vocabulary and reflects a lack of economic understanding (‘economic rationality’) shared by all sides, which put strict limits on the ability of fourth-century emperors to manage the economy in any real sense. Diocletian’s measures went far beyond those of previous emperors in their imaginative perception of what was needed, and they were continued to some extent by Constantine, but modern references to a ‘command economy’ or a totalitarian state mistake the letter for the reality. Rather, we should read the threats of provincial governors directed against tax collectors who failed in their duty as a symptom of actual powerlessness.

By his administrative reforms, Diocletian also laid the foundations of the late Roman bureaucratic system, whose object was to achieve tighter governmental control of all aspects of running the empire – fiscal, legal and administrative. It may be doubted whether the new system achieved its aim, though the original conception cannot be blamed for that. First, provincial government was reorganized; military and civil commands were separated, and each province henceforth had both a military commander (dux) and a civil governor. The provinces themselves were reduced in size and greatly enlarged in number: according to Lactantius, ‘to ensure that terror was universal, Diocletian cut the provinces into fragments’ (DMP 7.4). In fact the aim was to secure greater efficiency by shortening the chain of communications and command, and in so doing to reduce the power of individual governors. Inscriptions show that the process took some time; a list in a manuscript from Verona, known as the Laterculus Veronensis, or Verona List, indicates how far it had gone shortly after Diocletian’s abdication in AD 305. To give only two examples, Britain now had four provinces, Spain six and ‘Africa’ seven; the twelve larger units (dioceses) were governed by equestrian ‘vicars’ (vicarii) representing the praetorian prefects, who at the end of the reign of Constantine lost their military role and became the heads of the civil administration. Many of the laws in the Theodosian Code are addressed by the emperors to the praetorian prefects, who then had the task of passing the information on to the provincial governors. The praetorian prefects varied in number but for much of the fourth century there were three, four after AD 395. Under Diocletian the prefect was effectively the emperor’s second-in-command, with military, financial, legislative and administrative responsibility; from Constantine’s reign the military side was put under magistri militum (Masters of the Soldiers), who had command of the army and to whom the duces (military commanders in the provinces) were answerable. Below the prefects and vicars were provincial governors of various ranks, with titles such as praeses, proconsul, consularis and corrector. Rome and, later, Constantinople too, were outside the system, being governed by prefects of their own (praefecti urbis, prefects of the city). The system sounds neat and tidy, but as A. H. M. Jones points out, in practice it was constantly being circumvented, with constitutions addressed to ordinary governors and other direct communication not observing the theoretical chain of command. As time went on it was also circumvented by other means – patronage, bribery and less obvious forms of corruption. One should also be careful not to make too many assumptions based on modern preconceptions; the late Roman administration is scarcely comparable to a modern bureaucracy.

This system of provincial government required large numbers of officials to run it. In addition there were the so-called palatini, the financial officers of the largitiones and the res privata, part of the comitatus (the imperial entourage), along with the eunuch officials of the sacrum cubiculum (emperor’s bedchamber), the quaestor sacri palatii (imperial secretary), the magister officiorum (Master of Offices), who originated under Constantine and had control of what may be called the secretariat (the scrinia, comprising the epistolae, the memoria and the libelli), and probably also the agentes in rebus, the imperial couriers, and the comes of the domestici, the palace guard – all, naturally, with their own staffs. This group, of which the above is a highly simplified and incomplete sketch, travelled with the emperor, as did the imperial mint and wagon trains of bullion and luggage of all kinds. It all sounds very impressive, but in fact it had developed piecemeal over a considerable period, so that there was much actual confusion and duplication of duties. The officials themselves were collectively regarded as belonging to a militia and received military rations and pay, which made imperial service highly desirable for the hard-pressed members of the town councils, especially as they then gained release from their tax burdens. The late Roman government had therefore to strike a balance that guaranteed that enough good men were recruited into the imperial service, while ensuring that a sufficient number of taxpayers remained.

There are many problems in understanding the late Roman administrative system, which maintained an uneasy balance between bureaucracy and patronage; in particular, the number of those who were actually involved, and who were thus removed from the productive base and had instead to be supported (‘idle mouths’, to adopt the term used by A. H. M. Jones), has often been seen as a major factor in economic decline. These questions are discussed further in Chapter VII; meanwhile, we can note that by no means all of the system later known actually originated with Diocletian, though he is usually blamed for creating a top-heavy bureaucracy, just as he is for increasing the army to a size impossible for the empire to sustain.

Many of the changes that were taking place during his reign were in fact more a matter of long-term evolution than of individual initiative. It is often suggested, for example, that senators were excluded from posts in the provincial administration under Diocletian, who, like many other third-century emperors, had himself risen through the ranks of the army. But epigraphic evidence shows that senators were never excluded altogether; the fact that they were few in number at this period is a result not so much of imperial prejudice as of the decentralized conditions of the third century, which disrupted the existing patronage system, brought military commanders increasingly to the fore, and diminished the importance of the senate as an institution by locating the centre of government elsewhere than at Rome. Large numbers of extra provincial governors were needed to run the vastly increased number of provinces under Diocletian, and it is not surprising if they were in the first instance mainly of equestrian origin; the majority of provinces were accordingly placed under equestrian praesides. The separation of civil and military commands also doubled the amount of personnel needed. But senators were still used, for instance as correctores, regional governors in Italy. The distinction of title was kept, and when senatorial governors were reintroduced into a number of provinces by Constantine they were called consulares to distinguish them from the praesides, all of which suggests that the changes came about more for reasons of convenience and circumstance than of principle.