Imperial Roman Army

Imperial Roman army

Imperial Roman army

Imperial Roman Army Imperial Roman Army

Roman infantry helmet (Imperial Gallic type). Late 1st century Roman infantry helmet (Imperial Gallic type). Late 1st century Active

Active 30 BC - 284 AD30 BC - 284 AD Country

Country Roman EmpireRoman Empire Branch

Branch ArmyArmy

Size

Size 450,000 at peak in 211 AD450,000 at peak in 211 AD Unit types

Unit types Roman legions, Auxilia, Pretorian GuardRoman legions, Auxilia, Pretorian Guard Disbanded

Disbanded Became the late Roman armyBecame the late Roman army

The

The Imperial Roman armyImperial Roman armyrefers to the armed forces deployed by the Roman Empire during the Principate era (30refers to the armed forces deployed by the Roman Empire during the Principate era (30

BC

BC _–  – AD 284).AD 284). Under the founder

Under the founder _–  – emperor Augustus (ruled 30 BCemperor Augustus (ruled 30 BC _–  – AD 14 ), the legions, which were formations numbering aboutAD 14 ), the legions, which were formations numbering about 5,000 heavy infantry recruited from Roman citizens only, were transformed from a mixed conscript and volunteer 5,000 heavy infantry 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 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 term. (Conscription was only decreed in emergencies.) In the later 1st century, the size of a legion's First Cohort was doubled, increasing the strength of a legion to about 5,500.

doubled, increasing the strength of a legion to about 5,500.

To complement the legions, Augustus established the auxilia, a regular corps of similar numbers to the legions, To complement the legions, Augustus established the auxilia, a regular corps of similar numbers to the legions, recruited from the

recruited from the peregrini peregrini or non-citizen inhabitants of the empire, who constituted about 90% of the Empire'sor non-citizen inhabitants of the empire, who constituted about 90% of the Empire's

population in the 1st century. In addition to large numbers of heavy infantry equipped in a similar manner to population in the 1st century. In addition to large numbers of heavy infantry equipped in a similar manner to legionaries, the auxilia provided virtually all the army's cavalry, light infantry, archers and other specialists. The legionaries, the auxilia provided virtually all the army's cavalry, light infantry, archers and other specialists. The auxilia were organised in units about 500 strong. These units were termed

auxilia were organised in units about 500 strong. These units were termed cohortescohortesif they consisted of infantry,if they consisted of infantry, alaealae

if they consisted of cavalry and

if they consisted of cavalry and cohortes equitataecohortes equitatae if they were composed of infantry with a cavalry contingentif they were composed of infantry with a cavalry contingent

attached. attached.

Until about AD 68, the auxilia were recruited by a mix of conscription and voluntary enlistment. After that time, the Until about AD 68, 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 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 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. term, auxiliaries were awarded Roman citizenship, which carried important legal, fiscal and social advantages. Around AD 80, a minority of auxiliary regiments were doubled in size.

Around AD 80, a minority of auxiliary regiments were doubled in size.

Alongside the regular forces, the army of the Principate employed allied native units (called

Alongside the regular forces, the army of the Principate employed allied native units (called numerinumeri) from outside) from outside

the Empire on a mercenary basis. These were led by their own aristocrats and equipped in traditional fashion. 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

Numbers fluctuated according to circumstances and are largely unknown.largely unknown.

As all-citizen formations, and symbolic protectors of the dominance of the Italian "master-nation", legions enjoyed As all-citizen formations, and symbolic protectors of the dominance of the Italian "master-nation", legions enjoyed greater social prestige than the auxilia for much of the Principate. This was reflected in better pay and benefits. In greater social prestige than the auxilia for much of the Principate. This was reflected in better pay and benefits. In

addition, legionaries were equipped with more expensive and protective armour than auxiliaries, notably the

addition, legionaries were equipped with more expensive and protective armour than auxiliaries, notably the loricalorica segmentata

segmentata, or laminated-strip armour. However, in 212, the Emperor Caracalla granted Roman citizenship to nearly, or laminated-strip armour. However, in 212, the Emperor Caracalla granted Roman citizenship to nearly

all the Empire's freeborn inhabitants. At this point, the distinction between legions and auxilia became moot, the all the Empire's freeborn 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  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.

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 number

By the end of Augustus' reign, the imperial army number ed some 250,ed some 250,000 men, equally split between 25 legions and000 men, equally split between 25 legions and 250 units of auxiliaries. The numbers grew to a peak of about 450,000 by 211, in 33 legion

250 units of auxiliaries. The numbers grew to a peak of about 450,000 by 211, in 33 legion s and abous and about 400 auxiliaryt 400 auxiliary units. By then, auxiliaries outnumbered le

units. By then, auxiliaries outnumbered legionaries sgionaries substantially. From this peak, numbers probably underwent aubstantially. From this peak, numbers probably underwent a steep decline by 270 due to plague and losses during multiple major barbarian invasions. Numbers were restored to steep decline by 270 due to plague and losses during multiple major barbarian invasions. Numbers were restored to their early 2nd-century level of c. 400,000 (but probably not to their 211 peak) under Diocletian (r. 284-305). After their early 2nd-century level of c. 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 AD 68, virtually all military units the Empire's borders became settled (on the Rhine-Danube line in Europe) by AD 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 (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

in the reign of Hadrian (r. 117 _–  – 138).138).

The military chain of command was relatively flat. In each province, the deployed legions'

The military chain of command was relatively flat. In each province, the deployed legions' legatilegati (legion(legion

commanders, who also controlled the auxiliary units attached to their legion) reported to the

commanders, who also controlled the auxiliary units attached to their legion) reported to the legatus Augusti prolegatus Augusti pro  praetore

 praetore (provincial governor), who also headed the civil administration. The governor in turn reported directly to(provincial governor), who also headed the civil administration. The governor in turn reported directly to

the Emperor in Rome. There was no general staff in Rome, but the leading

the Emperor in Rome. There was no general staff in Rome, but the leading  praefectus praetorio praefectus praetorio (commander of the(commander of the

Praetorian Guard) often acted as the Emperor's

Praetorian Guard) often acted as the Emperor's de factode factomilitary chief-of-staff.military chief-of-staff.

Compared to the subsistence-level peasant families from which they mostly originated, legionary rankers enjoyed Compared to the subsistence-level peasant families from which they mostly originated, legionary rankers enjoyed considerable disposable income, enhanced by periodical cash bonuses on special occasions such as the accession of a 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 servic

new emperor. In addition, on completion of their term of service, they were ge, they were given a generous discharge bonusiven a generous discharge bonus equivalent to 13 years' salary. Aux

equivalent to 13 years' salary. Aux iliariesiliaries were paid much lesswere paid much less in the early 1in the early 1st century, but by 100 AD, thest century, but by 100 AD, the differential had virtually disappeared

differential had virtually disappeared. Simil. Similarly, in the earlier period, auxiliaries appear not to have received casharly, in the earlier period, auxiliaries appear not to have received cash and discharge bonuses, but probably did so from the reign of Hadrian onwards. Junior officers (

and discharge bonuses, but probably did so from the reign of Hadrian onwards. Junior officers ( principales principales), the), the

equivalent of non-commissioned officers in modern armies, could expect to earn up to twice basic pay. Legionary equivalent of non-commissioned officers in modern armies, could expect to earn up to twice basic pay. Legionary centurions, the equivalent of senior warrant officers, were organ

centurions, the equivalent of senior warrant officers, were organ ised in anised in an elabelaborate hierarorate hierarchy. Usually promotedchy. Usually promoted from the ranks, they commanded the legion's tactical sub

from the ranks, they commanded the legion's tactical sub -units of -units of cencenturiaeturiae (about 80 men) and cohorts (about 480(about 80 men) and cohorts (about 480

men). They were paid several multiples of basic pay. The most senior centurion, the

men). They were paid several multiples of basic pay. The most senior centurion, the primu primus piluss pilus, wa, was automaticallys automatically

elevated to equestrian rank on completion o

elevated to equestrian rank on completion o f his singlef his single-year term of office. The senior officers of the army, the-year term of office. The senior officers of the army, the legatilegati legionis

legionis (legion commanders),(legion commanders), tribuni militumtribuni militum (legion staff officers) and the(legion staff officers) and the praefecti praefecti (commanders of auxiliary(commanders of auxiliary

regiments) were all of at least equestrian rank. In the 1st and early 2nd centuries, they were mainly Italian aristocrats 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

performing the military component of their cursus honorumcursus honorum (conventional career-path). Later, provincial career(conventional career-path). Later, provincial career

officers became predominant. Senior officers were paid enormous salaries, multiples of at least 50 times a soldier's officers became predominant. Senior officers were paid enormous salaries, multiples of at least 50 times a soldier's basic pay.

basic pay.

Soldiers spent only a fraction of their lives

Soldiers spent only a fraction of their lives on campaigon campaign. Most of their time was spent on routine military duties suchn. 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 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 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 military and civil infrastructure. In addition of fit men, they played a crucial role in the construction of a province's military and civil infrastructure. In addition to constructing forts and fortified defences such as Hadrian's Wall, they built roads, bridges, ports, public buildings to constructing forts and fortified defences such as Hadrian's Wall, they built roads, bridges, ports, public buildings and entire new cities (colonia), and cleared forests and drained marshes to expand a province's available arable land. and entire new cities (colonia), and cleared forests and drained marshes to expand a province's available arable land. Soldiers, mostly drawn from polytheistic

Soldiers, mostly drawn from polytheistic societies, esocieties, enjoyed wide freedom of worship in the polytheistic Romannjoyed wide freedom of worship in the polytheistic Roman system. Only a few cults were banned by the Roman authorities, as being incompatible with the official Roman system. Only a few cults were banned by the Roman authorities, as being incompatible with the official Roman religion or being politically subversive, notably Druidism and Christianity. The later Principate saw the rise in religion or being 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 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 cult in the army was Mithraism, an apparently syncretist cult divulged only to initiates. By far the most popular cult in the army was Mithraism, an apparently syncretist cult which mainly originated in Asia Minor.

Sources

Sources

Section of Trajan's Column, Rome, showing the spiral Section of Trajan's Column, Rome, showing the spiral friezes that represent the best surviving evidence of the friezes that represent the best surviving evidence of the

equipment of imperial Roman soldiers equipment of imperial Roman soldiers

Surviving fragment of a Roman military diploma found Surviving fragment of a Roman military diploma found

at

atCarnuntumCarnuntumin the province of Noricum (Austria)in the province of Noricum (Austria)

Specimen Vindolanda tablets Specimen Vindolanda tablets

Except for the early 1st century, the literary evidence for the Except for the early 1st century, the literary evidence for the Principate period is surprisingly thin, due to the loss of a large Principate period is surprisingly thin, due to the loss of a large number of contemporary historical works. From the point of view number of contemporary historical works. From the point of view of the imperial army, the most useful sources are: firstly, works by of the imperial army, the most useful sources are: firstly, works by the general Caius Julius Caesar,

the general Caius Julius Caesar, De  De Bello Bello GallicoGallico andand De  De BelloBello Civili

Civili, covering his conquest of Gaul (58-50 BC) and his civil war, covering his conquest of Gaul (58-50 BC) and his civil war

against rival general Pompey (49-48 BC), respectively. Strictly against rival general Pompey (49-48 BC), respectively. Strictly speaking, these wars pre-date the army's imperial period (which speaking, these wars pre-date the army's imperial period (which started in 30 BC), but Caesar's detailed accounts are close enough started in 30 BC), but Caesar's detailed accounts are close enough in time to provide a wealth of information about organisation and in time to provide a wealth of information about organisation and tactics still relevant to the imperial legions. Secondly, works by tactics still relevant to the imperial legions. Secondly, works by the imperial-era historian Tacitus, writing around AD 100. These the imperial-era historian Tacitus, writing around AD 100. These are the

are the Annales Annales, a chronicle of the Julio-Claudian era from the, a chronicle of the Julio-Claudian era from the

death of the founder-emperor Augustus to that of Nero (AD death of the founder-emperor Augustus to that of Nero (AD 14-68). Even this suffers from large gaps, amounting to about a 14-68). Even this suffers from large gaps, amounting to about a third of the original; the

third of the original; the Historiae Historiae was the sequel to thewas the sequel to the Annales Annales,,

bringing the chronicle up to the death of Domitian (AD 96), of  bringing the chronicle up to the death of Domitian (AD 96), of  which only the first part, a detailed account of the Civil War of  which only the first part, a detailed account of the Civil War of  68-9 survives; and the

68-9 survives; and the  Agricola Agricola, a biography of Tacitus' own, a biography of Tacitus' own

father-in-law, Gnaeus Julius Agricola, who as governor of Britain father-in-law, Gnaeus Julius Agricola, who as governor of Britain (AD 78-85) attempted to subjugate Caledonia (Scotland) to (AD 78-85) attempted to subjugate Caledonia (Scotland) to Roman rule. The third important literary source is

Roman rule. The third important literary source is De Re  De Re MilitariMilitari,,

a treatise on Roman military practices by Vegetius, written c. 400. a treatise on Roman military practices by Vegetius, written c. 400. This contains much useful material relating to the Principate This contains much useful material relating to the Principate period, but the author's statements are undated and sometimes period, but the author's statements are undated and sometimes unreliable. Also useful are:

unreliable. Also useful are: The Jewish War The Jewish War  by Josephus, anby Josephus, an

eyewitness account of the First Jewish revolt of AD 66-70 by one eyewitness account of the First Jewish revolt of AD 66-70 by one of the Jewish commanders who defected to the Romans after he of the Jewish commanders who defected to the Romans after he was captured; the essay

was captured; the essay Acies contra Alanos Acies contra Alanos (( Ektaxis kata Alanon Ektaxis kata Alanon))

by the Greek author Arrian, who was imperial governor of  by the Greek author Arrian, who was imperial governor of  Cappadocia in AD 135-8: this describes a campaign led by the Cappadocia in AD 135-8: this describes a campaign led by the author to repel an invasion of his province by the Alans, an Iranic author to repel an invasion of his province by the Alans, an Iranic people of the Caucasus region. But most Roman historians present people of the Caucasus region. But most Roman historians present only a very limited picture of the imperial army's affairs, as they only a very limited picture of the imperial army's affairs, as they describe only military campaigns and say little about the army's describe only military campaigns and say little about the army's organisation, logistics and the daily lives of the troops. organisation, logistics and the daily lives of the troops. Fortunately, the thin and fragmentary literary evidence has been Fortunately, the thin and fragmentary literary evidence has been complemented by a vast mass of inscription and archaeological complemented by a vast mass of inscription and archaeological evidence.

evidence.

The imperial army was a highly bureaucratised institution. The imperial army was a highly bureaucratised institution. Meticulous financial records were kept by units'

Meticulous financial records were kept by units' corniculariicornicularii

(book-keepers). Detailed records were kept on all individual (book-keepers). Detailed records were kept on all individual soldiers and there is evidence of filing systems.

soldiers and there is evidence of filing systems.[1][1]Even minor matters such as soldiers' requests to theirEven minor matters such as soldiers' requests to their praefectus praefectus

for leave (

Hadrian's Wall, it can be deduced that the Roman garrison in the province of Britain alone generated tens of millions Hadrian's Wall, it can be deduced that the Roman garrison in the province of Britain alone generated tens of millions of documents.

of documents.[3][3] However, only an infinitesimal fraction of this vast documentation has survived, due to organicHowever, only an infinitesimal fraction of this vast documentation has survived, due to organic decomposition of the writing-medium (wooden and wax-tablets and papyrus). The only region of the empire where decomposition of the writing-medium (wooden and wax-tablets and papyrus). The only region of the empire where the army's documentation has survived in significant quantities is Egypt, where exceptionally dry conditions have the army's documentation has survived in significant quantities is Egypt, where exceptionally dry conditions have prevented decomposition. Egyptian papyri are thus a crucial source for the army's internal organisation and life. The prevented decomposition. Egyptian papyri are thus a crucial source for the army's internal organisation and life. The Vindolanda tablets, documents inscribed on wooden tablets and preserved by unusual anoxic conditions, are a rare Vindolanda tablets, documents inscribed on wooden tablets and preserved by unusual anoxic conditions, are a rare corpus of army documents from the north-western part of the Empire. They consist of a series of letters and corpus of army documents from the north-western part of the Empire. They consist of a series of letters and memoranda between officers of three auxiliary regiments stationed in succession at Vindolanda AD 85

memoranda between officers of three auxiliary regiments stationed in succession at Vindolanda AD 85 _–  – 122. They122. They provide a valuable glimpse of the real lives and activities of the garrison of an auxiliary fort.

provide a valuable glimpse of the real lives and activities of the garrison of an auxiliary fort.[4][4]

A large corpus of inscription evidence has been preserved on inorganic materials such as metal or stone. A large corpus of inscription evidence has been preserved on inorganic materials such as metal or stone. Of outstanding importance are the bas-reliefs on monuments erected by emperors to record their

Of outstanding importance are the bas-reliefs on monuments erected by emperors to record their victorious wars. Thevictorious wars. The most notable example is Trajan's Column in Rome. Erected in 112 to celebrate the Emperor Trajan's successful most notable example is Trajan's Column in Rome. Erected in 112 to celebrate the Emperor Trajan's successful conquest of Dacia (101-7), the reliefs provide the most comprehensive and detailed portrayal of Roman military conquest of Dacia (101-7), the reliefs provide the most comprehensive and detailed portrayal of Roman military equipment and practice extant. Other examples include imperial triumphal arches (see List of Roman triumphal equipment and practice extant. Other examples include imperial triumphal arches (see List of Roman triumphal arches). Another major source on stone is the extensive corpus of recovered tombstones of Roman soldiers. These arches). Another major source on stone is the extensive corpus of recovered tombstones of Roman soldiers. These often carry reliefs showing the subject in

often carry reliefs showing the subject in full combat dress plus inscriptions containing a summary of full combat dress plus inscriptions containing a summary of his career (age,his career (age, units served, ranks held). Also important are dedications of votive altars by military personnel, which shed light on units served, ranks held). Also important are dedications of votive altars by military personnel, which shed light on the dedicator's religious beliefs. In the case of both tombstones and altars, officers are

the dedicator's religious beliefs. In the case of both tombstones and altars, officers are disproportionately represented,disproportionately represented, due to the substantial expense of such monuments.

due to the substantial expense of such monuments.

Notable metal documents are Roman military diplomas. A diploma was a bronze tablet issued, between c. AD 50 Notable metal documents are Roman military diplomas. A diploma was a bronze tablet issued, between c. AD 50 and 212 (when all free inhabitants of the empire were granted Roman citizenship) to an auxiliary soldier on and 212 (when all free inhabitants of the empire were granted Roman citizenship) to an auxiliary soldier on completion of his 25-year term of service to prove the award of citizenship to the holder and his family. A particular completion of his 25-year term of service to prove the award of citizenship to the holder and his family. A particular advantage of diplomas for historians

advantage of diplomas for historians is thatis that they are accurately datable. Diplomas also northey are accurately datable. Diplomas also normally list the names of mally list the names of  several auxiliary units which served in the same province at the same time, critical data on the deployment of  several auxiliary units which served in the same province at the same time, critical data on the deployment of  auxiliary units in the various provinces of the Empire at different times. Also usually recorded are: beneficiary's auxiliary units in the various provinces of the Empire at different times. Also usually recorded are: beneficiary's regiment, regimental commander's name, beneficiary's military rank, name of beneficiary, name of beneficiary's regiment, regimental commander's name, beneficiary's military rank, name of beneficiary, name of beneficiary's father and origin (nation, tribe or city); name of beneficiary's wife and name of her father and origin; and names of  father and origin (nation, tribe or city); name of beneficiary's wife and name of her father and origin; and names of  children granted citizenship. Over 800 diplomas have been recovered, although most in a fragmentary state. (Even children granted citizenship. Over 800 diplomas have been recovered, although most in a fragmentary state. (Even these, however, represent an infinitesimal fraction of the hundreds of thousands of diplomas which must have been these, however, represent an infinitesimal fraction of the hundreds of thousands of diplomas which must have been issued. Apart from natural corrosion, the main reason for this low recovery rate is that, prior due to the late 19th issued. Apart from natural corrosion, the main reason for this low recovery rate is that, prior due to the late 19th century, when their historical value was recognised, diplomas were almost invariably melted down when found in century, when their historical value was recognised, diplomas were almost invariably melted down when found in order to recover their copper content - indeed most were probably melted down in the period following 212).

order to recover their copper content - indeed most were probably melted down in the period following 212).

Finally, a mass of information has been uncovered by archaeological excavation of imperial military sites: legionary Finally, a mass of information has been uncovered by archaeological excavation of imperial military sites: legionary fortresses, auxiliary forts, marching-camps and other facilities such as signal-stations. A prime example is fortresses, auxiliary forts, marching-camps and other facilities such as signal-stations. A prime example is Vindolanda fort itself, where excavations began in the 1930s and continue in 2012 (under the grandson of the first Vindolanda fort itself, where excavations began in the 1930s and continue in 2012 (under the grandson of the first director, Eric Birley). Such excavations have uncovered details of the lay-out and facilities of military sites and director, Eric Birley). Such excavations have uncovered details of the lay-out and facilities of military sites and remains of military equipment.

remains of military equipment.

Background: the Caesarian Roman army

Background: the Caesarian Roman army

The army of the late Republic that Augustus took over on becoming sole ruler of the Empire in 30 BC consisted of a The army of the late Republic that Augustus took over on becoming sole ruler of the Empire in 30 BC consisted of a number of large (5,000-strong) formations called legions, which were composed exclusively of heavy infantry. The number of large (5,000-strong) formations called legions, which were composed exclusively of heavy infantry. The legion's light infantry (

legion's light infantry (velitesvelites) which had been deployed in earlier times (see Roman army of the mid-Republic), had) which had been deployed in earlier times (see Roman army of the mid-Republic), had

been phased out as had its contingent of cavalry. Legions were recruited from Roman citizens only (i.e.: from been phased out as had its contingent of cavalry. Legions were recruited from Roman citizens only (i.e.: from Italians and inhabitants of Roman colonies outside Italy), by regular conscription, although by 88 BC, a substantial Italians and inhabitants of Roman colonies outside Italy), by regular conscription, although by 88 BC, a substantial proportion of recruits were volunteers.

To remedy the deficiencies in capability of the legions (heavy and light cavalry, light infantry, archers and other To remedy the deficiencies in capability of the legions (heavy and light cavalry, light infantry, archers and other specialists), the Romans relied on a motley array of irregular units of allied troops, both composed of subject natives specialists), the Romans relied on a motley array of irregular units of allied troops, both composed of subject natives of the empire's provinces (called the

of the empire's provinces (called the peregrini peregriniby the Romans) and of bands supplied, often on a mercenary basis, byby the Romans) and of bands supplied, often on a mercenary basis, by

Rome's allied kings beyond the Empire's borders. Led by their own aristocrats and equipped in their own traditional Rome's allied kings beyond the Empire's borders. Led by their own aristocrats and equipped in their own traditional fashion, these native units varied widely in size, quality and reliability. Most would only be available for particular fashion, these native units varied widely in size, quality and reliability. Most would only be available for particular campaigns before returning home or disbanding.

campaigns before returning home or disbanding.

Foundation of the imperial army under Augustus (30 BC - AD 14)

Foundation of the imperial army under Augustus (30 BC - AD 14)

Statue of the founder-emperor Augustus in garb of  Statue of the founder-emperor Augustus in garb of 

military commander-in-chief  military commander-in-chief 

On gaining undisputed mastery over the Roman empire in 30 BC, On gaining undisputed mastery over the Roman empire in 30 BC, Augustus (sole rule 30 BC - AD 14) was left with an army which Augustus (sole rule 30 BC - AD 14) was left with an army which was bloated by extraordinary recruitment for the Roman civil wars was bloated by extraordinary recruitment for the Roman civil wars and at the same lacking a suitable organisation for the defence and and at the same lacking a suitable organisation for the defence and expansion of a vast empire. Even after disbanding most of his expansion of a vast empire. Even after disbanding most of his defeated adversary Mark Anthony's legions, Augustus had 50 defeated adversary Mark Anthony's legions, Augustus had 50 legions under his command, composed exclusively of Roman legions under his command, composed exclusively of Roman citizens i.e. by that time, of Italians and inhabitants of Roman citizens i.e. by that time, of Italians and inhabitants of Roman colonies outside Italy. Alongside these were a mass of irregular colonies outside Italy. Alongside these were a mass of irregular non-Italian allied units whose command, size and equipment non-Italian allied units whose command, size and equipment varied greatly. Some allied units came from provinces within the varied greatly. Some allied units came from provinces within the empire, others from beyond the imperial borders.

empire, others from beyond the imperial borders.

Legions Legions

The first priority was to reduce the number of legions to a The first priority was to reduce the number of legions to a sustainable level. 50 legions implied too high a recruitment burden sustainable level. 50 legions implied too high a recruitment burden for a male citizen-body only about two-million strong, especially for a male citizen-body only about two-million strong, especially as Augustus intended to create a long-term career force. The as Augustus intended to create a long-term career force. The Emperor retained just over half

Emperor retained just over half his legions, disbanding the rest andhis legions, disbanding the rest and settling their veterans in no less than 28 new Roman colonies. settling their veterans in no less than 28 new Roman colonies.[5][5] The number of legions remained close to that level throughout the The number of legions remained close to that level throughout the Principate (varying between 25 and 33 in number).

Principate (varying between 25 and 33 in number).[6][6]

Unlike the Republican legions, which were, in theory at least, temporary citizen-levies for the duration of particular Unlike the Republican legions, which were, in theory at least, temporary citizen-levies for the duration of particular wars, Augustus and his right-hand man Agrippa clearly envisioned their legions as permanent units composed of  wars, Augustus and his right-hand man Agrippa clearly envisioned their legions as permanent units composed of  career professionals. Under the late Republic, a Roman citizen

career professionals. Under the late Republic, a Roman citizen iunior iunior (i.e. male of military age: 16(i.e. male of military age: 16 _–  – 46 years) could46 years) could

legally be required to serve a maximum of sixteen years in the legions and a maximum of six years consecutively. legally be required to serve a maximum of sixteen years in the legions and a maximum of six years consecutively. The average number of years served was about ten. In 13 BC, Augustus decreed sixteen years as the

The average number of years served was about ten. In 13 BC, Augustus decreed sixteen years as the standard standard termterm

of service for legionary recruits, with a further four years as reservists (

of service for legionary recruits, with a further four years as reservists (evocatievocati). In AD 5, the standard term was). In AD 5, the standard term was

increased to twenty years plus five years in the reserves.

increased to twenty years plus five years in the reserves.[7][7]In the period following its introduction, the new term wasIn the period following its introduction, the new term was deeply unpopular with the troops. On Augustus' death in AD 14, the legions stationed on the rivers Rhine and deeply unpopular with the troops. On Augustus' death in AD 14, the legions stationed on the rivers Rhine and Danube staged major mutinies, and demanded, among other things, reinstatement of a sixteen-year term.

Danube staged major mutinies, and demanded, among other things, reinstatement of a sixteen-year term.[8][8]AugustusAugustus prohibited serving legionaries from marrying, a decree that remained in force for two centuries.

prohibited serving legionaries from marrying, a decree that remained in force for two centuries.[9][9]This measure wasThis measure was probably prudent in the early imperial period, when most legionaries were from Italy or the Roman colonies on the probably prudent in the early imperial period, when most legionaries were from Italy or the Roman colonies on the Mediterranean, and were required to serve long years far from home. This could lead to disaffection if they left Mediterranean, and were required to serve long years far from home. This could lead to disaffection if they left families behind. But from about AD 100 onwards, when most legions were based long-term in the same families behind. But from about AD 100 onwards, when most legions were based long-term in the same frontier-province and recruitment was primarily local, the prohibition of marriage became a legal encumbrance that frontier-province and recruitment was primarily local, the prohibition of marriage became a legal encumbrance that was largely ignored. Many legionaries formed stable relationships and brought up families. Their sons, although was largely ignored. Many legionaries formed stable relationships and brought up families. Their sons, although

illegitimate in Roman law and thus unable to inherit their fathers' citizenship, were nevertheless frequently admitted illegitimate in Roman law and thus unable to inherit their fathers' citizenship, were nevertheless frequently admitted to legions.

to legions. At the same tim

At the same time, the traditional ge, the traditional grant of land to retiring veterans was made replaceable by a cash discharge bonus,rant of land to retiring veterans was made replaceable by a cash discharge bonus, as there was no longer sufficient state-owned land (

as there was no longer sufficient state-owned land (ager publicusager publicus) in Italy to distribute. Unlike the Republic,) in Italy to distribute. Unlike the Republic, whichwhich

had relied primarily on conscription (i.e. compulsory levy), Augustus and Agrippa preferred volunteers for their had relied primarily on conscription (i.e. compulsory levy), Augustus and Agrippa preferred volunteers for their professional legions.

professional legions.[10][10] Given the onerous new term of service, it was necessary to offer a substantial bonus toGiven the onerous new term of service, it was necessary to offer a substantial bonus to attract sufficient citizen-recruits. In AD 5, the discharge bonus was set at 3,000

attract sufficient citizen-recruits. In AD 5, the discharge bonus was set at 3,000 denariidenarii..[11][11]This was a generous sumThis was a generous sum

equivalent to about 13 years' gross salary for a legionary of the time. To finance this major outlay, Augustus decreed equivalent to about 13 years' gross salary for a legionary of the time. To finance this major outlay, Augustus decreed a 5% tax on inheritances and 1% on auction-sales, to be paid into a dedicated

a 5% tax on inheritances and 1% on auction-sales, to be paid into a dedicated aerarium militareaerarium militare (military(military

treasury).

treasury).[12][12] However, veterans continued to be offered land instead of cash in Roman colonies established in theHowever, veterans continued to be offered land instead of cash in Roman colonies established in the newly annexed frontier provinces, where public land was plentiful (as a result of confiscations from defeated newly annexed frontier provinces, where public land was plentiful (as a result of confiscations from defeated indigenous tribes).

indigenous tribes).[13][13] This was another grievance behind the mutinies of 14 AD, as it effectively forced ItalianThis was another grievance behind the mutinies of 14 AD, as it effectively forced Italian veterans to settle far from their own country (or lose their bonus).

veterans to settle far from their own country (or lose their bonus).[14][14]The imperial authorities could not compromiseThe imperial authorities could not compromise on this issue, as the planting of

on this issue, as the planting of colonies of Roman veterans was a crucial mechanism for controlling colonies of Roman veterans was a crucial mechanism for controlling and Romanisingand Romanising a new province, and the foundation of veterans' colonies did not cease until the end of Trajan's rule (117).

a new province, and the foundation of veterans' colonies did not cease until the end of Trajan's rule (117).[13][15][13][15]ButBut as legionary recruitment became more localised (by AD 60, over half of recruits were not Italian-born), the issue as legionary recruitment became more localised (by AD 60, over half of recruits were not Italian-born), the issue became less relevant.

became less relevant.[16][16] Augustus modi

Augustus modified the commandfied the command structure of the legion to reflect its new permanent, professional nature. Instructure of the legion to reflect its new permanent, professional nature. In Republican tradition (but ever less in practice), each l

Republican tradition (but ever less in practice), each l egion was under six equestrian military tribunes who tookegion was under six equestrian military tribunes who took turnsturns to command it pairs. But in the late Republic, military tribunes were eclipsed by higher-ranking officers of senatorial to command it pairs. But in the late Republic, military tribunes were eclipsed by higher-ranking officers of senatorial rank called

rank calledlegatilegati("literally "envoys"). A proconsul (Republican governor) might ask the senate to appoint a number("literally "envoys"). A proconsul (Republican governor) might ask the senate to appoint a number

of 

of legatilegati to serve under him e.g. Julius Caesar, Augustus' grand-uncle and adoptive father, had 5, and later 10,to serve under him e.g. Julius Caesar, Augustus' grand-uncle and adoptive father, had 5, and later 10, legatilegati

attached to his staff when he was governor of Cisalpine Gaul (58-51 BC). These commanded detachments of one or attached to his staff when he was governor of Cisalpine Gaul (58-51 BC). These commanded detachments of one or more legions at the governor's behest and played a critical role in the conquest of Gaul. But legions still lacked a more legions at the governor's behest and played a critical role in the conquest of Gaul. But legions still lacked a single, permanent commander.

single, permanent commander.[17][17]This was provided by Augustus, who This was provided by Augustus, who appointed aappointed a legatuslegatusto command each legionto command each legion

with a term of office of several years. The ranking senatorial military tribune (

with a term of office of several years. The ranking senatorial military tribune (tribunus militum laticlaviustribunus militum laticlavius) was) was

designated deputy commander, while the remaining five equestrian tribunes served as the legatus' staff officers. In designated deputy commander, while the remaining five equestrian tribunes served as the legatus' staff officers. In addition, Augustus established a new post of 

addition, Augustus established a new post of  praefectus castrorum praefectus castrorum (literally "prefect of the camp"), to be filled by a(literally "prefect of the camp"), to be filled by a

Roman knight (often an outgoing

Roman knight (often an outgoing centurio primus piluscenturio primus pilus, a legion's chief centurion, who was usually elevated to, a legion's chief centurion, who was usually elevated to

equestrian rank on completion of his single-year term of office).

equestrian rank on completion of his single-year term of office).[12][12] Technically, this officer ranked below theTechnically, this officer ranked below the senatorial tribune, but his long operational experience made him the legion commander's

senatorial tribune, but his long operational experience made him the legion commander's de factode facto executiveexecutive

officer.

officer.[18][18]The prefect's primary role was as the legion's quartermaster, in charge of legionary camps and supplies.The prefect's primary role was as the legion's quartermaster, in charge of legionary camps and supplies. It has been suggested that Augustus was responsible for establishing the tiny cavalry contingent of 120 horse It has been suggested that Augustus was responsible for establishing the tiny cavalry contingent of 120 horse attached to each legion.

attached to each legion.[19][19] The existence of this unit is attested in Josephus'The existence of this unit is attested in Josephus' Bellum Iudaicum Bellum Iudaicum written after AD 70,written after AD 70,

and on a number of tombstones.

and on a number of tombstones.[20][20]The attribution to Augustus is based on The attribution to Augustus is based on the (unproven) assumption that legionarythe (unproven) assumption that legionary cavalry had completely disappeared in the Caesarian army. The Augustan era also saw the introduction of some cavalry had completely disappeared in the Caesarian army. The Augustan era also saw the introduction of some items of more sophisticated and protective equipment for legionaries, primarily to improve their survival rate. The items of more sophisticated and protective equipment for legionaries, primarily to improve their survival rate. The

lorica segmentata

lorica segmentata (normally called simply "the(normally called simply "the loricalorica" by the Romans), was a special laminated-strip body-armour," by the Romans), was a special laminated-strip body-armour,

was probably developed under Augustus. Its earliest depiction is on the Arch of Augustus at Susa (Western Alps), was probably developed under Augustus. Its earliest depiction is on the Arch of Augustus at Susa (Western Alps), dating from 6 BC.

dating from 6 BC.[21][21]The oval shield of the Republic was replaced by the convex rectangular shield (The oval shield of the Republic was replaced by the convex rectangular shield (scutumscutum) of the) of the

imperial era. imperial era.

Auxilia Auxilia

Augustus' ambitious expansion plans for the Empire (which included advancing the European border to the lines of  Augustus' ambitious expansion plans for the Empire (which included advancing the European border to the lines of  the Elbe and Danube rivers) soon proved that 28 legions were not sufficient. Starting with the Cantabrian Wars, the Elbe and Danube rivers) soon proved that 28 legions were not sufficient. Starting with the Cantabrian Wars, which aimed to annex the mineral-rich mountains of north-western Spain, Augustus' 44-year sole rule saw an almost which aimed to annex the mineral-rich mountains of north-western Spain, Augustus' 44-year sole rule saw an almost uninterrupted series of major wars that frequently stretched the army's manpower to the limit.

uninterrupted series of major wars that frequently stretched the army's manpower to the limit. Augustus retained the services of numerous units of irregular allied native troops.

Augustus retained the services of numerous units of irregular allied native troops.[16][16] But there wasBut there was an urgent needan urgent need for extra regular troops, organised, if not yet equipped, in the same way as the legions. These could only be drawn for extra regular troops, organised, if not yet equipped, in the same way as the legions. These could only be drawn from the Empire's vast pool of non-citizen subjects, known as

from the Empire's vast pool of non-citizen subjects, known as peregrini peregrini..[22][22] These outnumbered Roman citizens byThese outnumbered Roman citizens by

around nine to one in the early 1st century. The

around nine to one in the early 1st century. The peregrini peregrini were now recruited into regular units of cohort-strength (c.were now recruited into regular units of cohort-strength (c.

500 men), to form a non-citizen corps called the

500 men), to form a non-citizen corps called the auxiliaauxilia (literally: "supports"). By AD 23, Tacitus reports that the(literally: "supports"). By AD 23, Tacitus reports that the

auxilia numbered roughly as many as the legionaries (i.e. c. 175,000 men).

auxilia numbered roughly as many as the legionaries (i.e. c. 175,000 men).[23][23]The roughly 250 regiments of auxiliaThe roughly 250 regiments of auxilia this implies were divided into three types: an all-infantry

this implies were divided into three types: an all-infantry cohorscohors (plural:(plural: cohortescohortes) (cohort) (c. 120 regiments); an) (cohort) (c. 120 regiments); an

infantry unit with a cavalry contingent attached, the

infantry unit with a cavalry contingent attached, the cohors equitatacohors equitata (plural:(plural:cohortes equitataecohortes equitatae) (80 units); and an) (80 units); and an

all-cavalry

all-cavalryalaala(plural:(plural:alaealae, literal meaning: "wing"), of which c. 50 were originally established., literal meaning: "wing"), of which c. 50 were originally established.[24][25][24][25]

It appears that at this early stage, auxiliary recruitment was ethnically based, with most men originating from the It appears that at this early stage, auxiliary recruitment was ethnically based, with most men originating from the same tribe or province. Hence regiments carried an ethnic name e.g.

same tribe or province. Hence regiments carried an ethnic name e.g. cohors V Raetorumcohors V Raetorum ("5th Cohort of Raeti"),("5th Cohort of Raeti"),

recruited from the Raeti, a group of Alpine tribes that inhabited modern Switzerland. It has been suggested that the recruited from the Raeti, a group of Alpine tribes that inhabited modern Switzerland. It has been suggested that the equipment of auxiliary regiments was not standardised until after AD 50, and that until then, auxiliaries were armed equipment of auxiliary regiments was not standardised until after AD 50, and that until then, auxiliaries were armed with the traditional weaponry of their tribe.

with the traditional weaponry of their tribe.[26][26] But it is possible that at least some regiments had standardisedBut it is possible that at least some regiments had standardised equipment from Augustan times.

equipment from Augustan times.

Auxiliary regiments were designed to operate as a complement to the legions. That is, they performed exactly the Auxiliary regiments were designed to operate as a complement to the legions. That is, they performed exactly the same role as the Republic's

same role as the Republic's alaealaeof Italian allies (of Italian allies (sociisocii) before the Social War (91-88 BC), an equal number of which) before the Social War (91-88 BC), an equal number of which

always accompanied legions on campaign. always accompanied legions on campaign.

Praetorian Guard and other forces based in Rome Praetorian Guard and other forces based in Rome

Praetorian Guard Praetorian Guard

Under the late Republic, a proconsul on campaign often formed a small personal guard, selected from the troops Under the late Republic, a proconsul on campaign often formed a small personal guard, selected from the troops under his com

under his command, knomand, known as awn as a cohors praetoriacohors praetoria ("commander's cohort"), from("commander's cohort"), from  praetorium praetorium meaning themeaning the

commander's tent at the centre of a Roman marching-camp (

commander's tent at the centre of a Roman marching-camp ( or commander's residence in a legionary fortress). At theor commander's residence in a legionary fortress). At the Battle of Actium (31 BC), Augustus had five such cohorts around him. After the battle, he retained t

Battle of Actium (31 BC), Augustus had five such cohorts around him. After the battle, he retained t hem in being ashem in being as a permanent brigade in and around Rome, known as the

a permanent brigade in and around Rome, known as the praetoriani praetoriani ("soldiers of the imperial palace"). Inscription("soldiers of the imperial palace"). Inscription evidence suggests that Augustus increased the Praetorian establishment to nine cohorts, each under the command of  evidence suggests that Augustus increased the Praetorian establishment to nine cohorts, each under the command of  aa tribunus militumtribunus militum (military tribune).(military tribune).[27][27] With all the legions deployed in far-off provinces under the command of With all the legions deployed in far-off provinces under the command of 

powerful senators, Augustus evidently considered that he needed a least one legion-sized force with him in Rome to powerful senators, Augustus evidently considered that he needed a least one legion-sized force with him in Rome to deter potential usurpers. Augustus stationed three cohorts in the City itself, each housed in separate barracks, and the deter potential usurpers. Augustus stationed three cohorts in the City itself, each housed in separate barracks, and the rest in neighbouring cities of Latium. Originally, each cohort was independent, but in 2 BC, Augustus appointed two rest in neighbouring cities of Latium. Originally, each cohort was independent, but in 2 BC, Augustus appointed two overall commanders (

overall commanders ( praefecti praetorio praefecti praetorio) of equestrian rank, one for the ) of equestrian rank, one for the cohorts based in the City, the other for cohorts based in the City, the other for thosethose

outside. outside.[28][28]

Augustus envisaged the Praetorians as an elite force, whose duties included guarding the imperial palace on the Augustus envisaged the Praetorians as an elite force, whose duties included guarding the imperial palace on the Palatine hill, protecting the Emperor's person and those of his family, defending the imperial government, and Palatine hill, protecting the Emperor's person and those of his family, defending the imperial government, and accompanying the emperor when he left the City on long journeys or to lead military campaigns in person. They also accompanying the emperor when he left the City on long journeys or to lead military campaigns in person. They also served as ceremonial troops on state

served as ceremonial troops on state occasions. Recruits to the ranks were, during occasions. Recruits to the ranks were, during the Julio-Claudian era, exclusivelythe Julio-Claudian era, exclusively Italian-born. They were accorded much better pay and conditions than ordinary legionaries. In AD 5, the standard Italian-born. They were accorded much better pay and conditions than ordinary legionaries. In AD 5, the standard term of service for Praetorians was set at 16 years (compared to 25 years in the legions), and their pay was set at term of service for Praetorians was set at 16 years (compared to 25 years in the legions), and their pay was set at triple the rate of ordinary legionaries.

boundaries of the City of Rome, Augustus laid down a rule that Praetorians on duty within the City must not wear boundaries of the City of Rome, Augustus laid down a rule that Praetorians on duty within the City must not wear armour and must keep their weapons out of sight.

armour and must keep their weapons out of sight.[30][30] Those Praetorians on important official duties, such as theThose Praetorians on important official duties, such as the Emperor's bodyguard-detail, wore the formal dress of Roman citizens, the toga, under which they concealed their Emperor's bodyguard-detail, wore the formal dress of Roman citizens, the toga, under which they concealed their swords and daggers.

swords and daggers.[31][32][31][32] The rest wore the soldier's standard non-combat dress of tunic and cloakThe rest wore the soldier's standard non-combat dress of tunic and cloak (( paludamentum paludamentum).).[33][33]

Urban cohorts Urban cohorts

In addition to the praetorians, Augustus established a second armed force in Rome, the

In addition to the praetorians, Augustus established a second armed force in Rome, the cohortes urbanaecohortes urbanae ("urban("urban

cohorts"), of which three were based in the City and one in

cohorts"), of which three were based in the City and one in Lugdunum Lugdunum(Lyon) in Gaul, to protect the major imperial(Lyon) in Gaul, to protect the major imperial

mint there. These battalions were tasked with maintaining public order in the City, including crowd-control at major mint there. These battalions were tasked with maintaining public order in the City, including crowd-control at major events such as chariot-races and gladiatorial combats, and the suppression of the popular unrest that periodically events such as chariot-races and gladiatorial combats, and the suppression of the popular unrest that periodically shook the City e.g. the riots caused by high grain prices in AD 19.

shook the City e.g. the riots caused by high grain prices in AD 19.[34][34]Their command was given to theTheir command was given to the praefectus praefectus urbi

urbi, a senator who acted as Rome's "mayor". Unlike the praetorians, the urban cohorts were not deployed for, a senator who acted as Rome's "mayor". Unlike the praetorians, the urban cohorts were not deployed for

military operations outside Italy. military operations outside Italy.[35][35]

German bodyguards German bodyguards

To double-insu

To double-insure hisre his own personal safety and that of imperial family members, Augustus established a smallown personal safety and that of imperial family members, Augustus established a small personal guard called the

personal guard called the Germani corporis custodesGermani corporis custodes ("German Bodyguards Regiment"). Probably of ("German Bodyguards Regiment"). Probably of 

cohort-strength, these were crack horsemen recruited from native peoples on the lower Rhine, mainly from the cohort-strength, these were crack horsemen recruited from native peoples on the lower Rhine, mainly from the Batavi. Their leader, probably a Batavi aristocrat, answered to the Emperor alone. The Germans shared the task of  Batavi. Their leader, probably a Batavi aristocrat, answered to the Emperor alone. The Germans shared the task of  guarding the imperial palace and family with the praetorians.

guarding the imperial palace and family with the praetorians.[29][29] In AD 68, the Emperor Galba disbanded theIn AD 68, the Emperor Galba disbanded the German Bodyguards Regiment because of their loyalty to Nero (ruled 54-68), whom he had overthrown. The German Bodyguards Regiment because of their loyalty to Nero (ruled 54-68), whom he had overthrown. The decision caused deep offence to the Batavi, and contributed to the outbreak of the Revolt of the Batavi in the decision caused deep offence to the Batavi, and contributed to the outbreak of the Revolt of the Batavi in the following year.

following year.[36][36]

Historical development

Historical development

Imperial expansion strategy Imperial expansion strategy

Under Augustus, the Europ

Under Augustus, the European bordeean borders of the empire he inherited from his grand-uncle Julius Caesar werers of the empire he inherited from his grand-uncle Julius Caesar were considerably expanded. During the first half of his sole rule (30

considerably expanded. During the first half of his sole rule (30 _–  – 9 BC), Augustus' central strategic objective9 BC), Augustus' central strategic objective was towas to advance the Roman b

advance the Roman borderorder from Illyricum and Macedonia to the line of the Danube, Europe's greatest river, in orderfrom Illyricum and Macedonia to the line of the Danube, Europe's greatest river, in order both to increase strategic depth between

both to increase strategic depth between thethe border and Italy and to provide a majoborder and Italy and to provide a majo r fluvial supplyr fluvial supply route for theroute for the Roman armies in the region. The strategy was successfully executed: Moesia (29-7 BC), Noricum (16 BC), Raetia Roman armies in the region. The strategy was successfully executed: Moesia (29-7 BC), Noricum (16 BC), Raetia (15 BC) and Pannonia (12-9 BC) were annexed in steady succession. After settling the Danube border, Augustus (15 BC) and Pannonia (12-9 BC) were annexed in steady succession. After settling the Danube border, Augustus turned his attention to the North, where Julius Caesar had in 51 BC established the border of Roman Gaul along the turned his attention to the North, where Julius Caesar had in 51 BC established the border of Roman Gaul along the river Rhine, the second major E

river Rhine, the second major European fluvial route.uropean fluvial route. Augustus launched an ambitious strategy of advancing theAugustus launched an ambitious strategy of advancing the Rhine border to the river Elbe, aiming to incorporate all the warlike West Germanic tribes. This would eliminate Rhine border to the river Elbe, aiming to incorporate all the warlike West Germanic tribes. This would eliminate their chronic threat to Gaul, incre

their chronic threat to Gaul, increase strategic depth between frase strategic depth between free Germans and Gaul, and make the westernee Germans and Gaul, and make the western Germans' formidable manpower available to the Roman army. But a massive and sustained military effort (6 BC Germans' formidable manpower available to the Roman army. But a massive and sustained military effort (6 BC --AD 9) came to

AD 9) came to nothinnothing. Roman advances in Germania Magna (i.e. Germany outside the empire) had to be scaledg. Roman advances in Germania Magna (i.e. Germany outside the empire) had to be scaled down during the Great Illyrian Revolt of AD 6-9, when many troops were diverted to Illyricum; and Augustus' down during the Great Illyrian Revolt of AD 6-9, when many troops were diverted to Illyricum; and Augustus' expansion strategy suffered a crushing setback when some 20,000 Roman troops were ambushed and massacred by expansion strategy suffered a crushing setback when some 20,000 Roman troops were ambushed and massacred by the Germans at the Battle of the Teutoberg Forest in AD 9. After this, Augustus shelved his Elbe strategy. It was the Germans at the Battle of the Teutoberg Forest in AD 9. After this, Augustus shelved his Elbe strategy. It was apparently revived briefly by his stepson and successor Tiberius, whose nephews, the generals Germanicus and apparently revived briefly by his stepson and successor Tiberius, whose nephews, the generals Germanicus and Drusus, launched major and successful operations in Germania in AD 14-17, during which the main tribes Drusus, launched major and successful operations in Germania in AD 14-17, during which the main tribes responsible for Varus' defeat were crushed and the three lost legionary

responsible for Varus' defeat were crushed and the three lost legionary aquilaeaquilae(eagle-standards) were recovered.(eagle-standards) were recovered.[37][37]

But Tiberius had clearly decided to keep the border at the Rhine by AD 16,

Germanic tribes as too powerful and rebellious to incorporate successfully into the empire. After this, plans to annex Germanic tribes as too powerful and rebellious to incorporate successfully into the empire. After this, plans to annex western Germania were never seriously revived by Augustus' successors. Under the Flavian emperors (69-96), the western Germania were never seriously revived by Augustus' successors. Under the Flavian emperors (69-96), the Romans occupied the trans-Rhenane region they called the

Romans occupied the trans-Rhenane region they called the  Agri  Agri DecumatesDecumates, roughly the territory of the modern, roughly the territory of the modern

German state of Baden-Württemberg. But this acquisition was aimed at shortening the lines of communication German state of Baden-Württemberg. But this acquisition was aimed at shortening the lines of communication between the legionary bases of Germania Superior and Raetia provinces (Mainz and Strasbourg in Germania Sup. between the legionary bases of Germania Superior and Raetia provinces (Mainz and Strasbourg in Germania Sup. and Augst and Regensburg in Raetia), by incorporating the salient between the upper reaches of the Rhine and and Augst and Regensburg in Raetia), by incorporating the salient between the upper reaches of the Rhine and Danube rivers: this annexation was not part of a broader strategy to annex western Germania.

Danube rivers: this annexation was not part of a broader strategy to annex western Germania. Doubtless min

Doubtless mindful of thdful of the e cocostly failstly failure of his Elbe strategy, Augustus reportedly included a clause in his willure of his Elbe strategy, Augustus reportedly included a clause in his will advising his successors not to attempt to expand the empire further.

advising his successors not to attempt to expand the empire further.[39][39]In the main, this advice was followed, andIn the main, this advice was followed, and few permanent annexations were made for the duration of the Principate. The main exceptions were Britain, which few permanent annexations were made for the duration of the Principate. The main exceptions were Britain, which was invaded by the emperor Claudius in AD 43 and was progressively subdued (as far as the Tyne-Solway line of  was invaded by the emperor Claudius in AD 43 and was progressively subdued (as far as the Tyne-Solway line of  the later Hadrian's Wall) in 43-78 (although the stiff, prolonged resistance offered by native tribes seemingly the later Hadrian's Wall) in 43-78 (although the stiff, prolonged resistance offered by native tribes seemingly confirmed Augustus' warning, and reportedly led the emperor Nero at one stage to seriously consider withdrawing confirmed Augustus' warning, and reportedly led the emperor Nero at one stage to seriously consider withdrawing from Britain altogether);

from Britain altogether);[40][40] and Dacia, conquered by Trajan in 101-6. In both cases, it appears that, apart fromand Dacia, conquered by Trajan in 101-6. In both cases, it appears that, apart from imperial self-glorification, the primary motivations were probably the target-countries' mineral resources and imperial self-glorification, the primary motivations were probably the target-countries' mineral resources and considerations of strategic defence.

considerations of strategic defence.

Apart from Britain and Dacia, other major territorial acquisitions by ambitious emperors were swiftly abandoned by Apart from Britain and Dacia, other major territorial acquisitions by ambitious emperors were swiftly abandoned by their immediate successors, who took a more realistic view of the value and defensibility of the new possessions: their immediate successors, who took a more realistic view of the value and defensibility of the new possessions: 1.

1. In In BrBrititaiain, n, ggovernor Governor Gnaenaeus Juliusus Julius Agricola was in AAgricola was in AD 79 apparD 79 apparently aently authorised by euthorised by emperor Vespasian to launchmperor Vespasian to launch the conquest

the conquest of Caledoof Caledonia,nia, thus brinthus bringing the whole island under Roman rule.ging the whole island under Roman rule.[41][41]But in 85, by which timeBut in 85, by which time Agricola's troops had probably advanced as far north as Inverness, the project was apparently cancelled by the Agricola's troops had probably advanced as far north as Inverness, the project was apparently cancelled by the emperor Domitian. Agricola was dismissed and

emperor Domitian. Agricola was dismissed and archaeology shows that the Romans abondoned the archaeology shows that the Romans abondoned the ScottishScottish Highlands and withdrew to the Forth-Clyde isthmus; and that by 110, Roman forts in the Scottish Lowlands had Highlands and withdrew to the Forth-Clyde isthmus; and that by 110, Roman forts in the Scottish Lowlands had also been evacuated, returning the border to the Tyne-Solway line. This prompted Agricola's son-in-law, the also been evacuated, returning the border to the Tyne-Solway line. This prompted Agricola's son-in-law, the historian Tacitus, to comment that "the complete subjugation of Britain was achieved but immediately given up" historian Tacitus, to comment that "the complete subjugation of Britain was achieved but immediately given up" (( perdomita Britannia et statim missa perdomita Britannia et statim missa..[42][42](Two further attempts to annex the Lowlands - by Antoninus Pius (r.(Two further attempts to annex the Lowlands - by Antoninus Pius (r.

138-61), who built the Antonine Wall along the Forth-Clyde isthmus, and by Septimius Severus (r. 197-211), 138-61), who built the Antonine Wall along the Forth-Clyde isthmus, and by Septimius Severus (r. 197-211), were likewise abandoned by their

were likewise abandoned by their successors).successors). 2.

2. The Parthian province of The Parthian province of Mesopotamia, annexed Mesopotamia, annexed by Trajan in 116, wby Trajan in 116, was evacuated by as evacuated by his successor Hhis successor Hadrian inadrian in 118.

118. 3.

3. HadriHadrian also wian also withdrewthdrew, by 126 (cf: the e, by 126 (cf: the establstablishmeishment of thent of the Limes Transalutanus Limes Transalutanus), from a large portion of ), from a large portion of 

Decebal's former Dacian kingdom, shortly after its conquest in 107 by Trajan: Moldavia, eastern Wallachia and Decebal's former Dacian kingdom, shortly after its conquest in 107 by Trajan: Moldavia, eastern Wallachia and the Banat (SE Hungarian Plain) were abandoned to Free Dacian and Sarmatian tribes. The most likely reason was the Banat (SE Hungarian Plain) were abandoned to Free Dacian and Sarmatian tribes. The most likely reason was that these regions did not possess significant mineral resources and were considered too difficult to defend. that these regions did not possess significant mineral resources and were considered too difficult to defend. 4.

4. MarcuMarcus Aures Aurelius' lius' reportreported plaed plans to ans to annexnnexSarmatiaSarmatia(i.e. the Hungarian Plain, which formed a salient between(i.e. the Hungarian Plain, which formed a salient between

Roman Pannonia and Dacia, then under the control of the warlike Iazyges Sarmatian tribe) and

Roman Pannonia and Dacia, then under the control of the warlike Iazyges Sarmatian tribe) and Marcomannia Marcomannia

(Bavaria/Austria north of the Danube, the territory of the Marcomanni and Quadi Germanic tribes) were only (Bavaria/Austria north of the Danube, the territory of the Marcomanni and Quadi Germanic tribes) were only partially accomplished by the time the emperor died in 180 and even these gains were promptly abandoned by his partially accomplished by the time the emperor died in 180 and even these gains were promptly abandoned by his son and successor Commodus.

son and successor Commodus.

In a different category are the Roman troops deployed to protect the Greek cities on the northern shores of the Black In a different category are the Roman troops deployed to protect the Greek cities on the northern shores of the Black sea (Pontus Euxinus). These cities controlled trade in the vital resources of the northern Black sea region (principally sea (Pontus Euxinus). These cities controlled trade in the vital resources of the northern Black sea region (principally grain from Sarmatia and metals from the Caucasus region. Pontic Olbia and the Roman client-states of the Bosporan grain from Sarmatia and metals from the Caucasus region. Pontic Olbia and the Roman client-states of the Bosporan kingdom and Colchis hosted Roman garrisons for much of the Principate era. But here the Romans relied on tame kingdom and Colchis hosted Roman garrisons for much of the Principate era. But here the Romans relied on tame native monarchies rather than direct annexation. By this means, the Black sea was turned into a Roman "lake" native monarchies rather than direct annexation. By this means, the Black sea was turned into a Roman "lake" inexpensively.