The Roman army (; Ancient Greek: ) is the generic term for the terrestrial armed forces deployed by the kingdom of Rome (to ca. 500 BC), the Roman Republic (500-31 BC), the Roman Empire (31 BC - AD 476) and its successor, the Byzantine empire (476-1453). It is thus a term that spans approximately 2,000 years, during which the Roman armed forces underwent numerous permutations in composition, organization, equipment and tactics, while conserving a core of lasting traditions.

Historical phases

The development of the Roman army may be divided into the following 8 historical phases: # The Early Roman army of the Roman kingdom and of the early Republic (to ca. 300 BC). During this period, when warfare chiefly consisted of small-scale plundering-raids, it has been suggested that the Roman army followed Etruscan or Greek models of organization and equipment. The early Roman army was based on an annual levy or conscription of citizens for a single campaigning-season, hence the term legion for the basic Roman military unit (derived from ''legere'', "to levy"). # The Roman army of the mid-Republic (a.k.a. as the "manipular army" or the "Polybian army" after the Greek historian Polybius, who provides the most detailed extant description of this phase) of the mid-Republican period (ca. 300-107 BC). During this period, the Romans, while maintaining the levy system, adopted the Samnite manipular organization for their legions and also bound all the other peninsular Italian states into a permanent military alliance (see ''Socii''). The latter were required to supply (collectively) roughly the same number of troops to joint forces as the Romans to serve under Roman command. Legions in this phase were always accompanied on campaign by the same number of allied ''alae'', units of roughly the same size as legions. # The Marian Roman army (107–30 BC) marks the transition between the conscription-based citizen-levy of the mid-Republic and the mainly volunteer, professional standing forces of the imperial era. During this period, quasi-standing armies were commanded by the ''imperatores'', powerful warlords such as Gaius Marius, Lucius Cornelius Sulla, Caesar, Pompey, and Mark Antony, who contested supreme power in numerous civil wars. As a result of the Social War (91-88 BC), all Italians were granted Roman citizenship and the old allied ''alae'' were abolished and its members integrated into the legions. Also, the citizen-cavalry of the Republic was much reduced in number and replaced by indigenous cavalry from the Roman provinces. # The Imperial Roman army (30 BC – AD 284), when the Republican system of temporary levies was replaced by a standing professional army of mainly volunteers. As established by the first Roman emperor, Augustus (sole ruler 30 BC - AD 14). The legions, now almost entirely large heavy infantry formations of 5,000-6,000 men) were still open only to Roman citizens (i.e. mainly the inhabitants of Italy and Roman colonies until AD 212). They were now flanked by the auxilia, a corps recruited mainly from ''peregrini'', imperial subjects who did not hold Roman citizenship (the great majority of the empire's inhabitants until 212, when all were granted citizenship). The ''auxilia'' were divided into much smaller formations of roughly ''cohort'' size (around 500 men). These contained not only heavy infantry as the legions, but also light infantry, heavy and light cavalry, archers and slingers. Both legions and auxilia regiments were mostly stationed along the empire's borders. # The Late Roman army (284–476 and its continuation, in the surviving eastern half of the empire, as the East Roman army to 641). In this phase, crystallised by the reforms of the emperor Diocletian (ruled 284-305), the Roman army returned to systematic conscription for most of its recruitment of citizens, while admitting large numbers of non-citizen barbarian volunteers. However, the army remained full-time professional and did not return to the short-term levies of the Republic. The old dual organisation of legions and auxilia was abandoned, with citizens and non-citizens now serving in the same units. The old legions were broken up into cohort or even smaller sizes. At the same time, a substantial proportion of the army's effectives were stationed in the interior of the empire, in the form of ''comitatus praesentales'', armies that escorted the emperors. # The Middle Byzantine army (641–1081), is the army of the Byzantine state in its classical form (i.e. after the permanent loss of its Near Eastern and North African territories to the Arab conquests after 641). This army was based on conscription of professional troops in the themes structure characteristic of this period, and from ca. 950 on the professional troops known as ''tagmata''. # The Komnenian Byzantine army, named after the Komnenos dynasty, which ruled in 1081–1185. This was an army built virtually from scratch after the permanent loss of Byzantium's traditional main recruiting ground of Anatolia to the Turks following the Battle of Manzikert in 1071, and the destruction of the last regiments of the old army in the wars against the Normans in the early 1080s. It survived until the fall of Constantinople to the Western crusaders in 1204. This army was characterised by a large number of mercenary regiments composed of troops of foreign origin such as the Varangian Guard, and the introduction of the ''pronoia'' system. # The Palaiologan Byzantine army, named after the Palaiologos dynasty (1261–1453), which ruled Byzantium between the recovery of Constantinople from the Crusaders and its fall to the Turks in 1453. Initially, it continued some practices inherited from the Komnenian era and retained a strong native element until the late 13th century. During the last century of its existence however, the empire was little more than a city-state that hired foreign mercenary bands for its defence. Thus the Byzantine army finally lost any meaningful connection with the standing imperial Roman army.

This article contains the summaries of the detailed linked articles on the historical phases above, Readers seeking discussion of the Roman army by theme, rather than by chronological phase, should consult the following articles:

History

Campaign history of the Roman military

Structural history of the Roman military

Corps

Praetorian Guard

Roman legion

Roman auxiliaries

Roman cavalry

Strategy and tactics

Defence-in-depth (Roman military)

Roman infantry tactics

Equipment & other

Roman military equipment

Roman military decorations and punishments

Some of the Roman armys many tactics are still used in modern day armies today.

Early Roman army (to ca. 300 BC)

Until ca. 550 BC, there was probably no "national" Roman army, but a series of clan-based war-bands which only coalesced into a united force in periods of serious external threat. Around 550 BC, during the period conventionally known as the rule of king Servius Tullius, it appears that a universal levy of eligible adult male citizens was instituted. This development apparently coincided with the introduction of heavy armour for most of the infantry. Although originally low in numbers the Roman infantry was extremely tactful and developed some of the most influential battle strategies to date.

The early Roman army was based on a compulsory levy from adult male citizens which was held at the start of each campaigning season, in those years that war was declared. There were probably no standing or professional forces. During the Regal Era (to ca. 500 BC), the standard levy was probably of 9,000 men, consisting of 6,000 heavily-armed infantry (probably Greek-style hoplites), plus 2,400 light-armed infantry (''rorarii'', later called ''velites'') and 600 light cavalry (''equites celeres''). When the kings were replaced by two annually-elected ''praetores'' in ca. 500 BC, the standard levy remained of the same size, but was now divided equally between the Praetors, each commanding one legion of 4,500 men.

It is likely that the hoplite element was deployed in a Greek-style phalanx formation in large set-piece battles. However, these were relatively rare, with most fighting consisting of small-scale border-raids and skirmishing. In these, the Romans would fight in their basic tactical unit, the ''centuria'' of 100 men. In addition, separate clan-based forces remained in existence until ca. 450 BC at least, although they would operate under the Praetors' authority, at least nominally....

In 493 BC, shortly after the establishment of the Roman Republic, Rome concluded a perpetual treaty of military alliance (the ''foedus Cassianum''), with the combined other Latin city-states. The treaty, probably motivated by the need for the Latins to deploy a united defence against incursions by neighbouring hill-tribes, provided for each party to provide an equal force for campaigns under unified command. It remained in force until 358 BC.

Roman army of the mid-Republic (ca. 300 – 107 BC)

The central feature of the Roman army of the mid-Republic, or the Polybian army, was the manipular organization of its battle-line. Instead a single, large mass (the phalanx) as in the Early Roman army, the Romans now drew up in three lines consisting of small units (maniples) of 120 men, arrayed in chessboard fashion, giving much greater tactical strength and flexibility. This structure was probably introduced in ca. 300 BC during the Samnite Wars. Also probably dating from this period was the regular accompaniment of each legion by an non-citizen formation of roughly equal size, the ''ala'', recruited from Rome's Italian allies, or ''socii''. The latter were ca. 150 autonomous states which were bound by a treaty of perpetual military alliance with Rome. Their sole obligation was to supply to the Roman army, on demand, a number of fully-equipped troops up to a specified maximum each year.

The Second Punic War (218–201 BC) saw the addition of a third element to the existing dual Roman/Italian structure: non-Italian mercenaries with specialist skills lacking in the legions and ''alae'': Numidian light cavalry, Cretan archers, and slingers from the Balearic islands. From this time, these units always accompanied Roman armies.

The Republican army of this period, like its earlier forebear, did not maintain standing or professional military forces, but levied them, by compulsory conscription, as required for each campaigning season and disbanded thereafter (although formations could be kept in being over winter during major wars). The standard levy was doubled during the Samnite Wars to 4 legions (2 per Consul), for a total of ca. 18,000 Roman troops and 4 allied ''alae'' of similar size. Service in the legions was limited to property-owning Roman citizens, normally those known as ''iuniores'' (age 16–46). The army's senior officers, including its commanders-in-chief, the Roman Consuls, were all elected annually at the People's Assembly. Only ''equites'' (members of the Roman knightly order) were eligible to serve as senior officers. ''Iuniores'' of the highest social classes (''equites'' and the First Class of commoners) provided the legion's cavalry, the other classes the legionary infantry. The ''proletarii'' (those assessed at under 400 ''drachmae'' wealth) were ineligible for legionary service and were assigned to the fleets as oarsmen. Elders, vagrants, freedmen, slaves and convicts were excluded from the military levy, save in emergencies.

The legionary cavalry also changed, probably around 300 BC onwards from the light, unarmoured horse of the early army to a heavy force with metal armour (bronze cuirasses and, later, chain-mail shirts). Contrary to a long-held view, the cavalry of the mid-Republic was a highly effective force that generally prevailed against strong enemy cavalry forces (both Gallic and Greek) until it was decisively beaten by the Carthaginian general Hannibal's horsemen during the second Punic War. This was due to Hannibal's greater operational flexibility owing to his Numidian light cavalry.

The Polybian army's operations during its existence can be divided into 3 broad phases. (1) The struggle for hegemony over Italy, especially against the Samnite League (338–264 BC); (2) the struggle with Carthage for hegemony in the western Mediterranean Sea (264–201 BC); and the struggle against the Hellenistic monarchies for control of the eastern Mediterranean (201–91 BC). During the earlier phase, the normal size of the levy (including allies) was in the region of 40,000 men (2 consular armies of ca. 20,000 men each). At the height of 2nd Punic war, Roman deployment reached a peak of ca. 240,000.

For the vast majority of the period of its existence, the Polybian levy was at war. This led to great strains on Roman and Italian manpower, but forged a superb fighting machine. During the Second Punic War, fully two-thirds of Roman ''iuniores'' were under arms continuously. In the period after the defeat of Carthage in 201 BC, the army was campaigning exclusively outside Italy, resulting in its men being away from their home plots of land for many years at a stretch. They were assuaged by the large amounts of booty that they shared after victories in the rich eastern theatre. But in Italy, the ever-increasing concentration of public lands in the hands of big landowners, and the consequent displacement of the soldiers' families, led to great unrest and demands for land redistribution. This was successfully achieved, but resulted in the disaffection of Rome's Italian allies, who as non-citizens were excluded from the redistribution. This led to the mass revolt of the ''socii'' and the Social War (91-88 BC). The result was the grant of Roman citizenship to all Italians and the end of the Polybian army's dual structure: the ''alae'' were abolished and the ''socii'' recruited into the legions.

Marian Roman army (107 – 30 BC)

Imperial Roman army (30 BC – AD 284)

Under the founder–emperor Augustus (ruled 30 BC – 14 AD), the legions, ca. 5,000-strong all- heavy infantry formations recruited from Roman citizens only, were transformed from a mixed conscript and volunteer corps serving an average of 10 years, to all-volunteer units of long-term professionals serving a standard 25-year term (conscription was only decreed in emergencies). In the later 1st century, the size of a legion's First Cohort was doubled, increasing legionary personnel to ca. 5,500.

Alongside the legions, Augustus established the auxilia, a regular corps of similar numbers to the legions, recruited from the ''peregrini'' (non-citizen inhabitants of the empire - about 90% of the empire's population in the 1st century). As well as comprising large numbers of extra heavy infantry equipped in a similar manner to legionaries, the auxilia provided virtually all the army's cavalry (heavy and light), light infantry, archers and other specialists. The auxilia were organised in ca. 500-strong units called ''cohortes'' (all-infantry), ''alae'' (all-cavalry) and ''cohortes equitatae'' (infantry with a cavalry contingent attached). Around AD 80, a minority of auxiliary regiments were doubled in size. Until about 68 AD, the auxilia were recruited by a mix of conscription and voluntary enlistment. After that time, the auxilia became largely a volunteer corps, with conscription resorted to only in emergencies. Auxiliaries were required to serve a minimum of 25 years, although many served for longer periods. On completion of their minimum term, auxiliaries were awarded Roman citizenship, which carried important legal, fiscal and social advantages. Alongside the regular forces, the army of the Principate employed allied native units (called ''numeri'') from outside the empire on a mercenary basis. These were led by their own aristocrats and equipped in traditional fashion. Numbers fluctuated according to circumstances and are largely unknown.

As all-citizen formations, and symbolic garantors of the dominance of the Italian "master-nation", legions enjoyed greater social prestige than the auxilia. This was reflected in better pay and benefits. In addition, legionaries were equipped with more expensive and protective armour than auxiliaries, notably the ''lorica segmentata'', or laminated-strip armour. However, in 212, the emperor Caracalla granted Roman citizenship to all the empire's inhabitants. At this point, the distinction between legions and auxilia became moot, the latter becoming all-citizen units also. The change was reflected in the disappearance, during the 3rd century, of legionaries' special equipment, and the progressive break-up of legions into cohort-sized units like the auxilia.

By the end of Augustus' reign, the imperial army numbered some 250,000 men, equally split between legionaries and auxiliaries 25 legions and ca. 250 auxiliary regiments). The numbers grew to a peak of about 450,000 by 211 (33 legions and ca. 400 auxiliary regiments). By then, auxiliaries outnumbered legionaries substantially. From the peak, numbers probably underwent a steep decline by 270 due to plague and losses during multiple major barbarian invasions. Numbers were restored to their early 2nd-century level of ca. 400,000 (but probably not to their 211 peak) under Diocletian (r. 284-305). After the empire's borders became settled (on the Rhine-Danube line in Europe) by 68, virtually all military units (except the Praetorian Guard) were stationed on or near the borders, in roughly 17 of the 42 provinces of the empire in the reign of Hadrian (r. 117-38).

The military chain of command was relatively flat. In each province, the deployed legions' ''legati'' (legion commanders, who also controlled the auxiliary regiments attached to their legion) reported to the ''legatus Augusti pro praetore'' (provincial governor), who also headed the civil administration. The governor in turn reported direct to the emperor in Rome. There was no army general staff in Rome, but the leading ''praefectus praetorio'' (commander of the Praetorian Guard) often acted as the emperor's ''de facto'' military chief-of-staff.

Legionary rankers were relatively well-paid, compared to contemporary common labourers. Compared with their subsistence-level peasant families, they enjoyed considerable disposable income, enhanced by periodical cash bonuses on special occasions such as the accession of a new emperor. In addition, on completion of their term of service, they were given a generous discharge bonus equivalent to 13 years' salary. Auxiliaries were paid much less in the early 1st century, but by AD 100, the differential had virtually disappeared. Similarly, in the earlier period, auxiliaries appear not to have received cash and discharge bonuses, but probably did so from Hadrian onwards. Junior officers (''principales''), the equivalent of NCO's in modern armies, could expect to earn up to twice basic pay. Legionary centurions, the equivalent of mid-level commissioned officers, were organised in an elaborate hierarchy. Usually risen from the ranks, they commanded the legion's tactical sub-units of ''centuriae'' (ca. 80 men) and cohorts (ca. 480 men). They were paid several multiples of basic pay. The most senior centurion, the ''primus pilus'', was elevated to equestrian rank on completion of his single-year term of offioe. The senior officers of the army, the ''legati legionis'' (legion commanders), ''tribuni militum'' (legion staff officers) and the ''praefecti'' (commanders of auxiliary regiments) were all of at least equestrian rank. In the 1st and early 2nd centuries, they were mainly Italian aristocrats performing the military component of their ''cursus honorum'' (coneventional career-path). Later, provincial career officers became predominant. Senior officers were paid enormous salaries, multiples of at least 50 times basic.

Soldiers spent only a fraction of their lives on campaign. Most of their time was spent on routine military duties such as training, patrolling, and maintenance of equipment etc. Soldiers also played an important role outside the military sphere. They performed the function of a provincial governor's police force. As a large, disciplined and skilled force of fit men, they played a crucial role in the construction of a province's Roman military and civil infrastructure: in addition to constructing forts and fortified defences such as Hadrian's Wall, they built roads, bridges, ports, public buildings, entire new cities (Roman colonies) and also engaged in large-scale forest clearance and marsh drainage to expand the province's available arable land.

Soldiers, mostly drawn from polytheistic societies, enjoyed wide freedom of worship in the polytheistic Roman system. They revered both their own native deities, Roman deities and the local deities of the provinces in which they served. Only a few religions were banned by the Roman authorities, as being incompatible with the official Roman religion and/or politically subversive, notably Druidism and Christianity. The later Principate saw the rise in popularity among the military of Eastern mystery cults, generally centred on one deity, and involving secret rituals divulged only to initiates. By far the most popular in the army was Mithraism, an apparently syncretist religion which mainly originated in Asia Minor.

Late Roman army/East Roman army (284–641)

The Late Roman army is the term used to denote the military forces of the Roman Empire from the accession of Emperor Diocletian in 284 until the Empire's definitive division into Eastern and Western halves in 395. A few decades afterwards, the Western army disintegrated as the Western empire collapsed. The East Roman army, on the other hand, continued intact and essentially unchanged until its reorganization by themes and transformation into the Byzantine army in the 7th century. The term "late Roman army" is often used to include the East Roman army.

The army of the Principate underwent a significant transformation as a result of the chaotic 3rd century. Unlike the Principate army, the army of the 4th century was heavily dependent on conscription and its soldiers were more poorly remunerated than in the 2nd century. Barbarians from outside the empire probably supplied a much larger proportion of the late army's recruits than in the army of the 1st and 2nd centuries.

The size of the 4th century army is controversial. More dated scholars (e.g. A.H.M. Jones, writing in the 1960s) estimated the late army as much larger than the Principate army, half the size again or even as much as twice the size. With the benefit of archaeological discoveries of recent decades, many contemporary historians view the late army as no larger than its predecessor: under Diocletian ca. 390,000 (the same as under Hadrian almost 2 centuries earlier) and under Constantine no greater, and probably somewhat smaller, than the Principate peak of ca. 440,000. The main change in structure was the establishment of large armies that accompanied the emperors (''comitatus praesentales'') and were generally based away from the frontiers. Their primary function was to deter usurpations. The legions were split up into smaller units comparable in size to the auxiliary regiments of the Principate. In parallel, legionary armour and equipment were abandoned in favour of auxiliary equipment. Infantry adopted the more protective equipment of the Principate cavalry.

The role of cavalry in the late army does not appear to have been enhanced as compared with the army of the Principate. The evidence is that cavalry was much the same proportion of overall army numbers as in the 2nd century and that its tactical role and prestige remained similar. Indeed, the cavalry acquired a reputation for incompetence and cowardice for their role in three major battles in mid-4th century. In contrast, the infantry retained its traditional reputation for excellence.

The 3rd and 4th centuries saw the upgrading of many existing border forts to make them more defensible, as well as the construction of new forts with much higher defensive specifications. The interpretation of this trend has fuelled an ongoing debate whether the army adopted a defence-in-depth strategy or continued the same posture of "forward defence" as in the early Principate. Many elements of the late army's defence posture were similar to those associated with forward defence, such as a loser forward location of forts, frequent cross-border operations, and external buffer-zones of allied barbarian tribes. Whatever the defence strategy, it was apparently less successful in preventing barbarian incursions than in the 1st and 2nd centuries. This may have been due to heavier barbarian pressure, and/or to the practice of keeping large armies of the best troops in the interior, depriving the border forces of sufficient support.

Byzantine army (641–1081)

Komnenian Byzantine army (1081–1204)

The Komnenian period marked a rebirth of the Byzantine army. At the beginning of the Komnenian period in 1081, the Byzantine Empire had been reduced to the smallest territorial extent in its history. Surrounded by enemies, and financially ruined by a long period of civil war, the empire's prospects looked grim.

At the beginning of the Komnenian period, the Byzantine army was reduced to a shadow of its former self: during the 11th century, decades of peace and neglect had reduced the old thematic forces, and the Battle of Manzikert in 1071 had destroyed the professional ''tagmata'', the core of the Byzantine army. At Manzikert and later at Dyrrhachium, units tracing their lineage for centuries back to Late Roman army were wiped out, and the subsequent loss of Asia Minor deprived the Empire of its main recruiting ground. In the Balkans, at the same time, the Empire was exposed to invasions by the Norman Kingdom of Sicily, and by Pecheneg raids across the Danube.

The Byzantine army's nadir was reached in 1091, when Alexios I could manage to field only 500 soldiers from the Empire's professional forces. These formed the nucleus of the army, with the addition of the armed retainers of Alexios' relatives and the nobles enrolled in the army and the substantial aid of a large force of allied Cumans, which won the Battle of Levounion against the Pechenegs (Petcheneks or Patzinaks). Yet, through a combination of skill, determination and years of campaigning, Alexios, John and Manuel Komnenos managed to restore the power of the Byzantine Empire by constructing a new army from scratch. This process should not, however, at least in its earlier phases, be seen as a planned exercise in military restructuring. In particular, Alexios I was often reduced to reacting to events rather than controlling them; the changes he made to the Byzantine army were largely done out of immediate necessity and were pragmatic in nature.

The new force had a core of units which were both professional and disciplined. It contained formidable guards units such as the Varangians, the ''Athanatoi'', a unit of heavy cavalry stationed in Constantinople, the ''Vardariotai'' and the ''Archontopouloi'', recruited by Alexios from the sons of dead Byzantine officers, foreign mercenary regiments, and also units of professional soldiers recruited from the provinces. These provincial troops included ''kataphraktoi'' cavalry from Macedonia, Thessaly and Thrace, and various other provincial forces such as Trebizond Archers from the Black Sea coast of Anatolia. Alongside troops raised and paid for directly by the state the Komnenian army included the armed followers of members of the wider imperial family and its extensive connections. In this can be seen the beginnings of the feudalisation of the Byzantine military. The granting of ''pronoia'' holdings, where land, or more accurately rights to revenue from land, was held in return for military obligations, was beginning to become a notable element in the military infrastructure towards the end of the Komnenian period, though it became much more important subsequently.

In 1097, the Byzantine army numbered around 70,000 men altogether. By 1180 and the death of Manuel Komnenos, whose frequent campaigns had been on a grand scale, the army was probably considerably larger. During the reign of Alexios I, the field army numbered around 20,000 men which was increased to about 30,000 men in John II's reign. By the end of Manuel I's reign the Byzantine field army had risen to 40,000 men.

Palaiologan Byzantine army (1261–1453)

The Palaiologan army refers to the military forces of the Byzantine Empire from the late 13th century to its final collapse in the mid 15th century, under the House of the Palaiologoi. The army was a direct continuation of the forces of the Nicaean army, which itself was a fractured component of the formidable Komnenian army. Under the first Palaiologan emperor, Michael VIII, the army's role took an increasingly offensive role whilst the naval forces of the Empire, weakened since the days of Andronikos I Komnenos, were boosted to include thousands of skilled sailors and some 80 ships. Due to the lack of land to support the army, the Empire required the use of large numbers of mercenaries.

After Andronikos II took to the throne, the army fell apart and the Byzantines suffered regular defeats at the hands of their eastern opponents, although they would continue to enjoy success against the crusader territories in Greece. By c. 1350, following a destructive civil war and the outbreak of the Black Death, the Empire was no longer capable of raising troops and the supplies to maintain them. The Empire came to rely upon troops provided by Serbs, Bulgarians, Venetians, Latins, Genoans and Ottoman Turks to fight the civil wars that lasted for the greater part of the 14th century, with the latter foe being the most successful in establishing a foothold in Thrace. The Ottomans swiftly expanded through the Balkans and cut off Constantinople, the capital of the Byzantine Empire, from the surrounding land. The last decisive battle was fought by the Palaiologan army in 1453, when Constantinople was besieged and fell on 29 May. The last isolated remnants of the Byzantine state were conquered by 1461.

Citations

See also

Military of ancient Rome

Roman legion

Roman auxiliaries

Equestrian order

List of Roman legions

List of Roman auxiliary regiments

Late Roman army

Byzantine army

East Roman army

Category:Military of ancient Rome

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