Benutzer:Autokrator/Spätrömische Armee

Vorlage:Expand Vorlage:RomanMilitary The Late Roman army refers to the military forces of the Roman Empire of the Dominate period, from the latter part of the 3rd century to the its reorganization into the thematic armies in the mid-7th century in the Eastern Empire.

Sources

Much of our evidence for the 4th century's army's unit deployments is contained in a single document, the Notitia Dignitatum, compiled ca. 395-420, a manual of all late Roman public offices, military and civil. Unfortunately, the Notitia gives us a confused and incomplete picture of the late 4th century army.Vorlage:Fact For the earlier part of the 4th century, it can only give an even more limited picture.Vorlage:Fact

The Notitia presents three main problems, as regards the study of the Empire's military establishment:

1. It was compiled at two different times. The Eastern section apparently dates from ca. 395 AD; the Western from considerably later, ca. 420. Furthermore, each section is probably not a contemporaneous "snapshot", but relies on data stretching back as far as twenty years. The Eastern section may contain data from as early as 379, the start of the rule of Theodosius I. The Western section contains data from as early as ca. 400: for example, it shows units deployed in Britain, which must date from before 410, when Roman troops were evacuated from the island. In consequence, there is substantial duplication, with the same unit often listed under different commands. It is impossible to ascertain whether these were detachments of the same unit in different places at the same time, at the same whole unit at different times. Also, it is likely that some units only existed on paper or contained just a skeleton personnel.
2. The Notitia has many sections missing and lacunae (gaps) within sections. This is doubtless due to accumulated text losses and copying errors as it was repeatedly copied over the centuries: the earliest manuscript we possess today dates from the 15th century. The Notitia cannot therefore provide a comprehensive listing of all units in existence.
3. The Notitia does not contain any personnel figures. Therefore, the size of individual units, and of the various commands, cannot be ascertained, as we have little other evidence of unit sizes at this time. In turn, this makes it impossible to assess accurately the overall size of the army. Depending on the strength of units, the late 4th century army may, at one extreme, have equalled the size of the 2nd century force (i.e. over 400,000 men); at the other extreme, it may have been far smaller. For example, the forces deployed in Britain ca. 400 may have been just 18,000 against ca. 55,000 in the 2nd century.

Despite these drawbacks, the Notitia remains the central source on the late Army's structure due to the dearth of other evidence.

The main literary source for the 4th century Army are the Res Gestae (History) of Ammianus Marcellinus, whose surviving books cover the period 353 to 378. Marcellinus, himself a veteran soldier, is regarded by scholars as a reliable and valuable source. But he largely fails to remedy the deficiencies of the Notitia as regards army and unit strength or units in existence, as he is rarely specific about either.

For the 6th century army of the East Roman empire, there are extant works of a number of contemporary authors, most prominent among them Procopius of Caesarea, who described in great detail the Wars of Reconquest of Justinian I.

The 4th century army

The army of the Principate, as it was established by the founder-emperor Augustus (ruled 30 BC - 14 AD) and survived until well into the 3rd century, consisted of two distinct corps. The legions were ca. 30 large formations of about 5,500 men, almost entirely infantry, which admitted only Roman citizens. The auxilia were ca. 450 much smaller units of about 500 men (a minority were up to 1,000 strong), which were divided into ca. 100 pure cavalry units (alae), ca. 100 pure infantry (cohortes) and ca. 250 mixed cavalry/infantry units (cohortes equitatae); some of these units were designated sagittariorum, meaning they contained archers. The auxilia thus contained almost all the Roman army's cavalry and archers, as well as approximately the same number of foot soldiers. The auxilia were mainly recruited from the peregrini (provincial subjects of the empire who did not hold Roman citizenship), but also admitted Roman citizens and barbari, the Roman term for peoples living outside the empire's borders.

The turbulent 3rd century saw some limited innovations, although the overall 2nd century configuration remained intact: (i) Septimius Severus (r.197-211) stationed legion II Parthica near Rome from 200 AD onwards, the first legion to be stationed in Italy since Augustus. This, together with the Praetorian Guard and an expanded imperial escort cavalry (equites singulares Augusti) added up to a substantial elite strike force of ca. 20,000 - the equivalent of 3 legions of infantry and 10 alae of cavalry- at the immediate disposal of the emperor. (ii) the emperor Gallienus (r. 260-8) appears to have deployed in the approaches to northern Italy a field army consisting of legionary detachments and elite cavalry units; the latter included detached cavalry contingents of some legions (equites promoti), some apparently new Dalmatian cavalry (equites Dalmatarum) and elements of allied cavalry (equites foederati). But both Severus' and Gallienus' armies should probably not be seen as strategic reserves, but rather as enhanced personal protection against usurpers. (iii) A small number of regular units appear in the record, bearing the names of barbarian tribes (as opposed to peregrini tribal names) for the first time. These were clearly foederati (allied troops under a military obligation to Rome) converted into regular units, a trend that was to accelerate in the 4th century e.g. the ala I Sarmatarum attested in Britain, probably composed of some of the 5,500 captured Sarmatian horsemen sent to garrison Hadrian's Wall by emperor Marcus Aurelius in c175.

The 2nd century configuration underwent major restructuring under the emperors Diocletian (r. 284-305) and Constantine I (r. 312-336), in parallel to a similarly wide-ranging reform of the administrative and social structure of the Empire. Under Diocletian, the separation of civil and military offices began, which was accompanied by the removal of the senatorial class from command and the rise of a "professional" officer corps. This was drawn mostly from the equestrian class, but also open to centurions and lower ranks (a notable example being Diocletian himself) through the existence of the collegium protectorum, a sort of staff academy.

Army size

Contrary to a long- and widely-held view, the overall size of the 4th century army probably did not exceed that of the 2nd century army at any stage. The fallacy that the 4th century army was much larger is based on two factors: underestimation of the size of the 2nd century army and overestimation of the unit sizes of the 4th century army.

It used to be thought that the auxilia of the 2nd century numbered roughly the same as the legionaries i.e. ca. 150,000 men, giving an overall army of ca. 300,000 (excluding fleets). But the increase in diploma and other evidence has led to the discovery of many more auxiliary units and the fact that as many as 70% of cohortes were equitatae i.e. possessed cavalry contingents and were thus 25% larger. The 2nd century auxilia are now believed to have numbered at least 220,000 effectives and may have been as many as 250,000, if allowance is made for the fact there were probably c50 units more than we have evidence for. Adding in the ca. 10,000 Praetorian Guards stationed in Rome, this gives a total for the 2nd century army of 380,000 - 410,000 (excluding fleets and Rome's public order guards: cohortes urbanae and vigiles).

From ancient sources, we have only one credible global figure for the 4th century army: 389,704 (excluding fleets) for the army of Diocletian. This is closely in line with the known strength of the 2nd century army. For the army of Constantine, estimates have been as high as 450,000 but are based on assumptions about unit sizes that are highly speculative e.g. the size of auxilia palatina elite infantry units, which may have been 1,000-strong like the old auxiliary cohortes milliariae or only 500-strong ordinary cohortes. Even if 450,000 is an accurate estimate for Constantine's army, it is only 10-15% greater than the 2nd century army: nowhere near the 33%, 50% or even 100% increases variously suggested by some scholars.

The only other global figure from antiquity, by the 6th century writer Agathias, is of 645,000 including fleets i.e. ca. 600,000 excluding fleets. This is dismissed by many historians today as it is not related to any specific period, and is part of a polemic, comparing (unfavourably) the much smaller army of his day. The Agathias figure was given some credibility by A.H.M. Jones' Later Roman Empire (1964), which remains the fundamental study of the late Roman army. Jones used papyri evidence to calculate the size of units deployed in Egypt under Diocletian. The papyri provided data on the total money (and grain) allocated for pay to each unit and to each individual. But Jones' figures for unit strength were sharply revised downwards by a rigorous review of the evidence by R. Duncan-Jones. Using these revised figures, Diocletian's army was likely much closer to 400,000 than to 600,000.

The figures discussed thus far refer to the official strength of the army. But it is important to bear in mind that units were in practice always under-strength. It appears, from the meagre evidence available, that this problem was considerably worse in the 4th century army than in the 2nd century. An average of 3 cohortes equitatae during the 2nd century yields actual numbers in service of 84% of the official strength. But the evidence for the 4th century indicates that actual numbers were on average only 66% of official. Thus if the 4th century army had an official strength of ca. 400,000, it probably had only ca. 275,000 actually in service at any given time. In contrast, the 2nd century army would in reality be substantially larger with ca. 340,000 effectives in service at all times. Even if the official size of the 4th century army reached 450,000 briefly under Constantine, the actual total would be ca. 300,000, still less than the 2nd century.

Structure

Structural changes were complex in detail, but two fundamental trends may be discerned: (1) the break-up of the legions into much smaller, and tactically more flexible, formations comparable to the earlier auxilia regiments or legionary vexillations; and (2) the grading of units by strategic role into more or lass static frontier forces and mobile field armies.

Under Diocletian, the number of legions, and probably of other units, appears to have more than doubled. But it is unlikely that overall army size increased as unit strengths appear to have been reduced, in some cases drastically. For example, there are legions in the mid-4th century that are documented with just 1,000 effectives, less than a fifth of their 2nd-century strength. A good illustration of the proliferation of units without any increase in overall army numbers is Diocletian's army in Egypt, as calculated by R. Duncan-Jones.

ROMAN ARMY DEPLOYMENT IN EGYPT

Unit type	No. of units	Unit strength	Total strength	XXXXX	Unit type	No. of units	Unit strength	Total strength
Early 2nd century					Early 4th century (Diocletian)
Legion	1	5,500	5,500		Legion (detachment)	13	550	7,150
Ala	6	480	2,880		Ala	22	120	2,640
Cohort	11	480	5,280		Cohort	12	160	1,920
					Equites	10	120	1,200
Total	18		13,660			57		12,910

The table shows that the 4th century deployment was actually slightly smaller than in the 2nd century, despite the number of units deployed having tripled (although it should be noted that some of the 4th century "units" were only detachments, not whole units). It is understandable how such proliferation of units could lead to inflated estimates of overall army size.

Under Constantine, the army's units appear to have been divided into 3 grades, according to their strategic role and, to a lesser extent, quality:

• praesentales or palatini, elite imperial escort troops which were based at or near the imperial capitals (Trier and Milan in the West; Sirmium, Constantinople and Nicomedia in the East) and accompanied the emperors on campaign. These were later complemented by the imperial guard units of the Scholae Palatinae. A comitatus praesentalis (escort army) was commanded by a magister militum (praesentalis) in the East and by a magister peditum in Italy and a magister equitum in Gaul (see below).

• comitatenses, mobile field army (comitatus) troops, composed mostly of infantry, and based well behind the border in key provinces. Field armies were commanded by magistri militum in the East and by comites (literally "companions" i.e. companions of the emperor) in the West. The comitatus were based in or near major cities. Although the comitatus are commonly described as "mobile field armies", their mobility should not be exaggerated: as Goldsworthy points out, they could move no faster than a marching infantryman, or indeed, than the ox-drawn wagons of their supply-train.

• limitanei or ripenses, static border troops stationed on the empire's frontiers, under the command of senior military officers called duces limitis ("border commanders"). In the past, it was generally thought that the limitanei were a part-time militia of local farmers, of poor combat capability. In reality, they were full-time professionals. Indeed, it was forbidden by law for them to work in the fields or herd animals. The view that limitanei were low-quality derives primarily from references in the legal codes, but it is unlikely that these give a balanced or contemporary picture (the Justinian Law Code was drawn up in the 6th century). Indeed, given that the limitanei were charged with combating the incessant small-scale barbarian raids that were the empire's enduring security problem, it is likely that their combat capability and experience were high. Most likely, they differed from higher-grade troops in that they were not trained for large-scale formation manoeuvres. Nonetheless, limitanei units often joined the comitatenses armies on campaign, sometimes staying on for long periods, classified as pseudocomitatenses.

Unit types also became more varied. Alongside the traditional legiones, alae and cohortes, there appear several new unit types, such as schola, vexillationes, cuneus and equites for the cavalry, and milites, numerus and auxilia (different from the Principate-era auxilia) for the infantry. There are no clear rules as to which unit type belonged to which grade (except that scholae were always praesentales). For example, new-style auxilia units could be either auxilia palatina - some of the best units in the late army or border units.

The strength of old and new-style units is very uncertain, and may have varied during the 4th century. Size may also have varied depending on the grade of the unit. Following are some estimates which take account of recent archaeological discovery:

ESTIMATED SIZE OF UNITS IN 4th CENTURY ARMY

Cavalry unit type	Palatini	Comitatenses	Limitanei	XXXXX	Infantry unit type	Palatini	Comitatenses	Limitanei
Ala			under 300		Auxilia	1,000-1,200	500-600
Cuneus					Cohors			under 300
Equites		500			Legio	1,000-1,200	1,000-1,200
Schola	500	X	X		Milites		500
Vexillatio	600	600			Numerus		1,000

In the Notitia Dignitatum, the structure of the high command is somewhat different in the West from the the East, although it must be borne in mind that the western section was compiled in ca. 420, when the western empire was in deep crisis and therefore the different command arrangements may reflect that situation.
Eastern empire: Reporting directly to the eastern emperor were 2 magistri militum praesentales (each in charge of a comitatus praesentalis or escort field army); and 3 magistri militum commanding the field armies of the dioceses (administrative divisions) of Oriens, Thraciae and Illyricum. Each of these magistri militum controlled the duces limitis border commanders) in his diocese.
Western empire: The western structure was more hierarchical. Reporting directly to the western emperor was just one field marshal, the magister peditum (literally: "master of infantry", but his army included cavalry) in charge of the field army in Italy. This officer was at various times also called the magister utriusque militiae (literally: "master of both services" i.e. of both cavalry and infantry, or commander-in-chief) or the patricius (an honorific title). Reporting in turn to the magister peditum was a magister equitum (literally "master of cavalry", but he also commanded infantry) who commanded the field army in Gaul. The magister equitum in turn controlled 5 comites (field army commanders), of Illyricum West, Britain, Spain, Tingitania and Africa. These comites in turn controlled the duces in their province. The duces in Gaul, however, probably reported direct to the magister equitum.

Role of cavalry

A traditional thesis is that cavalry assumed a much greater importance in the 4th century army than it enjoyed in the 2nd century. According to this view, cavalry increased significantly as a proportion of the total forces and took over the leading tactical role from the infantry. It also enjoyed much higher status than in the 2nd century. At the same time, the infantry declined in efficiency and value in operations. In fact, there is no good evidence to support this view, and plenty of evidence against it.

The thesis primarily claims support from the 3rd century developments stated above, Septimius Severus' enhanced cavalry escort and Gallienus' assembly of a large cavalry force, stationed in northern Italy. But the fact that two 3rd century emperors felt the need for greater personal protection as they moved around the empire (hardly surprising, given the chaotic period in question), does not imply that the role of cavalry changed in the army as a whole.

As regards numbers, the 2nd century army had ca. 80,000 cavalry out of ca. 380,000 total effectives (low count) i.e cavalry was 21% of the total forces. Estimating the cavalry share in the 4th century army is impeded by the fundamental problem that unit sizes are not known with any certainty. But we can attempt a "guesstimate" using some consensus assumptions about unit sizes (see table above)

FIELD ARMIES OF THE EAST ROMAN EMPIRE c395 AD

Army	Cavalry units	Infantry units	XXX	Total cavalry	Total infantry (A)	Total effectives (A)	XXX	Total cavalry	Total infantry (B)	Total effectives (B)
Praesentalis I	5 vexillationes palatinae 5 vexillationes comitatenses	6 legiones palatinae 18 auxilia palatina		6,000	26,400	32,400		6,000	16,500	22,500
Praesentalis II	6 vexillationes pal. 6 vexillationes comit.	6 legiones pal. 17 auxilia pal. 1 pseudocomit.		7,200	25,550	32,750		7,200	16,200	23,400
Comitatus Thraciarum	3 vexillationes pal. 4 vexillationes comit.	21 legiones comit.		4,200	23,100	27,300		4,200	23,100	27,300
Comitatus Illyrici	2 vexillationes comit.	1 legio pal. 8 legiones comit. 6 auxilia pal. 9 pseudocomit.		1,200	18,750	19,950		1,200	15,450	16,650
Comitatus Orientis	10 vexillationes comit.	9 legiones comit. 2 auxilia pal. 10 pseudocomit.		6,000	14,600	20,600		6,000	13,500	19,500
Total				24,600	108,400	133,000		24,600	84,750	109,350

Note: Effectives (A) refers to auxilia palatina strength of 1,100; (B) auxilia pal. 550. Pseudocomitatenses units assumed strength of 250.

The table shows that the proportion of cavalry in the field armies' total was thus in the range 18-22%: much the same proportion as in the 2nd century, indeed somewhat less if auxilia palatina units were 1,000-strong. There is thus no evidence for an increase in the relative importance of cavalry in the army. It should be noted, however, that in the eastern field army, cavalry was nearly a third of the total force. This is to be expected, as there they faced the mainly cavalry army of the Persians. It appears that in the 4th century there was a substantial increase in the number of heavily-armoured cavalry in the East (cataphracti and clibanarii).

The supposed higher status of cavalry in the 4th century is also open to doubt. This view is largely based on underestimating the importance of cavalry in the 2nd century. Cavalry always had greater prestige than infantry in the Principate: in the time of Domitian (r. 81-96), although an auxiliary infantryman (pedes cohortalis) was paid less than a legionary foot soldier, a cavalryman from a cohors equitata (eques cohortalis) was paid the same, and an elite ala cavalryman (eques alaris) 20% more.

Role of infantry

The idea that in the 4th century, cavalry was the main tactical arm, with an ineffectual infantry relegated to a subsidiary role, is also false. The table above shows that the field armies continued to be dominated by infantry. The latter included large numbers of crack infantry regiments with an awesome reputation, including the famed Batavi, still classified as elite after 400 years of service to the empire. The auxilia palatina were rated among the best regiments in the army.

Most battles fought by Roman forces in the 4th century continued to be essentially infantry encounters with cavalry playing a supporting role. A good illustration of the combat tactics of a 4th century field army is the Battle of Strasbourg in 357 AD, described by Ammianus. The Caesar (deputy emperor) Julian, in command of the comitatus Galliarum (field army of Gaul) of 13,000 men confronted a major raiding force of Alamanni Germans which outnumbered the Romans by 3 to 1. Julian's force was seriously understrength (due to losses in previous campaigns against the Germans) but high-quality, including elite infantry regiments of Batavi, Cornuti, Brachiati and Primani. The encounter took place on a rise a few miles from the river Rhine.

The Roman order of battle was a traditional array of infantry in the centre (drawn up in two lines, front and rear, spaced widely apart) and the cavalry (of unknown size, but, by implication, not more than c2,000) on the flank: in this case all the cavalry was stationed on the right flank, as the left flank was broken ground that was impassable to cavalry. The Roman cavalry included special heavily armoured cavalry called cataphracti. It is unclear what proportion of the total cavalry were cataphracti, but since Ammianus mentions them only, they may have been over half. The cataphracti were a serious threat to the lightly armoured German riders, and therefore to the German left flank as a whole. But the Alamanni's paramount leader, Chnodomar, had prepared a stratagem to deal with them. He ordered some lightly-armed warriors ride pillion with his horsemen. When the enemy cavalry was engaged, they were to leap down on foot, and stab the Romans' horses in the flanks, which unlike their riders, were unprotected.

As soon as the two armies were drawn up, battle began. The opposing infantry lines locked together in a fierce struggle, each side alternately advancing and retreating. The Roman cavalry engaged the German horsemen, but Chnodomar's stratagem paid dividends. The interspersed foot warriors wreaked havoc, bringing down the horses of the cataphracti and then killing their riders who, weighed down by their heavy armour, had little mobility on foot. Disconcerted by these tactics, the Roman cavalry panicked and then fled the field, taking refuge behind the infantry lines, where it took the personal intervention of Julian himself to rally them. This was the first critical moment, as the Roman front line's right flank was now exposed to assault by the victorious German cavalry. But the right wing was held by the crack Cornuti and Brachiati regiments who, despite being assailed by German foot and horse simultaneously, managed to hold formation until the regrouped Roman cavalry returned to relieve the pressure on the flank. Now Chnodomar and his fellow chiefs, in response to the loud demands of their followers, dismounted and led the main body of German foot warriors in an all-out assault on the Roman front line. The Germans charged straight at the serried ranks of Romans. But the Roman front line held for a long time, inflicting severe casualties on the Germans who flung themselves recklessly at the massed spears. Then, a group of German chiefs and their best warriors succeeded, by desperate efforts, in punching a hole through the centre of the Roman front line. This was potentially disastrous for the Romans. But despite being cut in two, the Roman front line did not collapse: the experienced frontline regiments managed to hold their formation. Meanwhile, a large number of Germans poured through the breach in the line and charged the centre of the Roman rear line. This position was held by the elite Primani legion, which stopped the German attack in its tracks. The Roman rear line, (whose right wing was held by the Batavi) then probably gradually closed inwards, encircled and then eliminated the Germans who had broken through. The breach in the front line was presumably filled, either by the separated wings of the front line reconnecting, or by rear line troops (Ammianus does not specify which). The front line, now reinforced by the rear line, began pushing the Germans back, and gradually hemmed them in from the flanks. At this point, the Germans were already exhausted and demoralised by their lack of progress and severe losses. Finally, after more hours of relentless pressure from the Romans, the German line collapsed: as panic spread through their ranks, the Germans broke formation and ran for their lives. Many did not run fast enough: pursued all the way to the Rhine by Roman cavalry and infantry, many were cut down as they ran and thousands more drowned as they tried to get across the river. The battle was thus won, as were countless battles in the centuries before it, by the discipline, training, skill and tenacity of the Roman foot soldiers.

Role of barbari in the army

Barbari ("barbarians") was the generic term used by the Romans to denote peoples resident beyond the borders of the empire, and best translates as "foreigners" (although it is derived from a Greek word meaning "to babble": a reference to their outlandish tongues). Barbari had played an important part in the army of the Principate throughout its history. Apart from ad hoc levies of troops from Rome's amici (satellite kings), it is likely that large irregular forces of barbarian-born troops, known as socii or foederati, were in semi-permanent service alongside the regular auxilia. We have no idea how many at any given time. In addition, most scholars believe that the regular auxilia themselves recruited significant numbers of barbari throughout their history.

But there is substantial evidence that the proportion of barbarian-born troops in the regular army may have increased sharply during the 4th century:

1. The Notitia lists a number of barbarian military settlements in the empire. Known as laeti or gentiles ("natives"), these were an important source of recruits for the army. Groups of Germanic or Sarmatian tribespeople were granted land to settle in the Empire, in return for military service. Most likely each community was under a treaty obligation to supply a specified number of troops to the army each year. Laeti settlements were outside the normal framework of the provincial administration, and under the control of specially-appointed Roman officials called praefecti laetorum. The latter were evidently military, rather than civilian officers, as they reported to a magister militum praesentalis (army field marshal). The settlements were thus essentially military cantons whose raison d'etre was to breed soldiers. The resettlement within the empire of barbarian tribespeople in return for military service was not a new phenomenon in the 4th century: it stretches back to the days of Augustus. The latter allowed a number of Germanic tribes, who felt threatened by their neighbours, to move from the eastern bank of the Rhine to the Roman-controlled western bank, e.g. the Cugerni,a branch of the Sugambri tribe, and the Ubii. The latter, who moved from the Taunus region to the area around Colonia Agrippina (Cologne), were specifically given the task of guarding their stretch of Rhine. In the late 2nd century, Marcus Aurelius settled large numbers of Quadi and Sarmatians in the Danubian provinces. But it does appear that the practice became more systematic and on a much larger scale in the 4th century.
2. The Notitia lists a large number of units with barbarian names. Among others, regiments of Franks, Saxons, Goths, Sarmatians, and Vandals are listed. This was the result of the transformation of irregular allied units serving under their own native officers (known as socii, or foederati) into regular formations. During the Principate, regular units with barbarian names are not attested until the 3rd century and even then rarely. (e.g. the ala I Sarmatarum attested in 3rd century Britain, doubtless an offshoot of the Sarmatian horsemen posted there in 175).
3. The emergence of significant numbers of senior officers with barbarian names in the regular army, and eventually in the high command itself. In the early 5th century, the Western Roman forces were often controlled by barbarian-born generals, such asArbogast, Stilicho and Ricimer.
4. The adoption by the 4th century army of barbarian (especially Germanic) dress, customs and culture, suggesting enhanced barbarian influence. For example, Roman army units adopted mock barbarian names (e.g. Cornuti = "horned ones", a reference to the German custom of attaching horns to their helmets) and the barritus, a German warcry.

Quantification of the proportion of barbarian-born troops in the 4th century army is highly speculative due to the lack of any statistical evidence such as that provided by military diplomas for the 2nd century. One recent estimate, based on the numbers of documented officers with barbarian names, suggests that ca. 25% of the 4th century army was barbarian-born. If this is an accurate estimate, then it is likely a much higher proportion than in the 2nd century regular army: if barbarian recruits were 25% of the overall 2nd century army, then they would have provided over 42% of the recruits to the 2nd century auxilia (which constituted 60% of the total army), as the legions were closed to non-citizens. There is no evidence that recruitment of barbarians was on such a scale in the 2nd century: what scant evidence exists suggests the vast majority of auxilia were Roman peregrini (second-class citizens). It is therefore likely that the 4th century army recruited barbarians in significantly greater numbers than in earlier centuries, although it is impossible to be certain: Heather, for one, believes there was no increase in barbarian recruitment.

Nevertheless, the growth of barbarian influence should not be exaggerated. Even if 25% of the army was barbarian, that leaves the great majority as Roman-born. Furthermore, the army remained overwhelmingly based on Roman military tradition and practice.

The barbarisation theory

The growth of barbarian influence gave rise to the theory that the army's discipline, reliability and effectiveness declined as a result, and was a major factor in the collapse of the western Roman empire. This view ultimately derives from Edward Gibbon's 18th-century magnum opus, The Decline and Fall of the Roman Empire.

According to this view, the barbarian officers and men recruited by the late army, coming from tribes that were traditional enemies of Rome, had no real loyalty to Rome and often betrayed her interests, colluding with invading barbarian tribes, especially if those tribes were their own. At the same time, the spread of barbarian customs and culture military led to a decline in traditional discipline, and internal army disunity due to friction between Romans and barbarians. Ultimately, the army degenerated into just a collection of foreign mercenary bands that were incapable of defending the empire effectively.

Evidence adduced for the barbarisation theory includes:

1. An incident, mentioned by Ammianus, when 3 high-ranking barbarian officers in Julian's army were alleged to have sent a secret warning to their fellow-tribesmen across the Rhine of a planned Roman operation against them.
2. The massacre of the families of barbarian foederati carried out by Roman troops in the wake of the overthrow of the barbarian magister utriusque militiae (army commander-in-chief) of the West Stilicho in 408. This supposedly proves the bitter divisions in the army caused by the barbarian presence.
3. The allegedly treacherous behaviour of a number of barbarian generalissimos: Arbogast, Stilicho, Ricimer in the West and Gainas in the East.

Sources

Primary

• Vegetius, De Re Militari
• Ammianus Marcellinus, Roman History
• Zosimus, Historia Nova
• Procopius, Histroy of the Wars

Secondary and tertiary

• Karen R. Dixon: The Late Roman Army. Routledge, 2000, ISBN 978-0-415-22296-9. 
• Hugh Elton: Warfare in Roman Europe, AD 350-425. Oxford University Press, 1998, ISBN 978-0-19-815241-5. 
• Paul (ed.) Erdkamp: A Companion to the Roman Army. Blackwell Publishing Ltd., 2007, ISBN 978-1-4051-2153-8. 
• Adrian Goldsworthy: Roman Warfare. 2000. 
• Adrian Goldsworthy: Complete Roman Army. 2005.