The imperial Roman army was arguably one of the most impressive fighting forces the world has ever known.

The imperial Roman army was arguably one of the most impressive fighting forces the world has ever known. Its military campaigns greatly expanded the territory of the Roman Empire. In the first century c.e., Rome began the conquest of Britain, and in the second century, it conquered Dacia, modern Romania, and parts of modern Jordan and Iraq. The Roman army also defended the Empire against a wide range of enemies along its frontiers, including the Caledonians in northern Britain, various Germanic tribes, the Sarmatians, the Parthians, the Sāsānian Persians, and desert peoples in North Africa. Roman soldiers were highly skilled in pitched battle, siegecraft, and military Engineers;Romanengineering. In the course of their campaigns Roman troops built military roads, bridges, and large permanent camps, many of which eventually became cities in Europe, the Middle East, and North Africa.Rome;EmpireRome;Empire

At Armor;RomanUniforms;Romanthe beginning of Augustus’s reign as emperor in 27 b.c.e., Roman legionary infantrymen wore a simple round Helmets;Romanhelmet with a horsehair tail at the top as well as a chain mail shirt known as a Lorica hamata (Roman chain mail shirt)lorica hamata. The latter consisted of interlocking metal rings and provided good protection but was, however, very heavy and took a long time to manufacture. Later in Augustus’s reign infantrymen began to use a new type of helmet, of Gallic origin, which was more closely fitted to the skull and included neck and cheek guards. In addition, possibly due to a major loss of military equipment in the German defeat of three legions in the Battle of Teutoburg Forest (9 Teutoburg Forest, Battle of (9 c.e.) c.e. ), the Roman infantry began to use a new type of breastplate known as the Lorica segmentata (Roman breastplate) lorica segmentata. This armor consisted of horizontal metal bands covering the chest and abdomen as well as vertical metal bands protecting the shoulders. This could be manufactured much more quickly than mail armor and was very flexible. However, the fittings that held the bands together were easily damaged; as a result, this type of armor was in constant need of repair. Early imperial infantrymen also wore Greaves greaves, or shin guards, on their legs as well as leather strips called Pteurages (thigh and arm guards) pteurages that were attached to their body armor and provided protection for their thighs and upper arms.

The principal weapon of early imperial legionary infantrymen was a short sword called a Gladius (sword)gladius, which was modeled after that of the Spanish Celts and used for hand-to-hand combat. Infantrymen also carried a javelin, or Pilum (spear) pilum, which was hurled at the enemy from a distance, as well as a thrusting spear known as a Hasta (spear) hasta. The large semicylindrical shield, or Scutum (shield) scutum, was probably of Celtic origin and derived from flat oval shields. By the first century c.e. its upper and lower curved edges had been removed, giving it a more rectangular shape. Legionary infantrymen were also equipped with a dagger, which, like the gladius, was of Spanish origin.

Roman officers of the early Empire wore the same Gallic-type helmets worn by the infantry and a variety of body armor, including mail shirts, cuirasses that were modeled after the human torso, or scale shirts known as Lorica squamata (Roman scale shirt)loricae squamatae. The latter consisted of overlapping metal scales arranged in horizontal rows and fastened to a foundation of linen or hide. This type of armor was easy to make and repair and, when polished, gave the wearer an impressive appearance. However, it was not very flexible, and its wearer was vulnerable to a sword or spear thrust from below.

Under the early Empire, troops of the auxilia used equipment that was generally inferior to that of the legionaries; however, they began to receive better-quality equipment during the reign of the emperor Trajan (Roman emperor) Trajan (c. 53-c. 117 c.e. ). The infantry wore a variety of helmets as well as leather tunics covered with metal plates or mail, and used narrow, flat, sometimes oval shields. Their principal weapons were the hasta and the Spatha (sword) spatha, a long sword that became the dominant form of sword throughout the Roman army by the early third century. Cavalrymen wore iron helmets that covered the entire head except for the eyes, nose, and mouth. They wore either mail or scale body armor and used the same weapons as did the infantry of the auxilia cohorts. Although they did not use stirrups, they were firmly anchored on horseback by the four projecting horns of their saddles.

During the crisis of the third century c.e. the Roman Empire experienced increased invasion and internal chaos but lacked a centralized military supply system. Armies were consequently forced to salvage equipment from battlefields or to obtain it on their own from other sources, which, in turn, led to an end to uniformity in the appearance of soldiers. During this period, the lorica segmentata was gradually abandoned, and soldiers increasingly made use of mail shirts as well as an improved form of scale armor. In this type of armor, which did not require a foundation, the scales were ringed together vertically as well as horizontally. The scales were therefore locked down, and the wearer was much less vulnerable to a thrust from below. Moreover, the older Gallic helmet was replaced by a new helmet of Sarmatian origin, the Spangenhelm (helmet)spangenhelm, which consisted of several metal plates held together in a conical shape by reinforcement bands. This helmet, which included cheek, neck, and nose guards, was used by both infantry and cavalry. In addition the scutum was replaced by a large-dished oval shield covered with hide or linen. Cavalry units used a similar type of shield that featured the insignia of the bearer’s unit.

In the late third century c.e., the emperor Diocletian (Roman emperor)Diocletian (c. 245-316 c.e.) established a series of state-run arms factories, or Fabricae (Roman arms factories)Arms manufacture, Romanfabricae, in an attempt to remedy the supply problem. However, these factories failed to restore uniformity in military equipment due to the fact that a wide range of barbarian peoples were serving in the Roman army by this time and used their own native weapons. In the fourth century the factories did mass-produce a new type of helmet of Parthian-Sāsānian origin, known as a ridge helmet, because it consisted of two metal halves held together by a central ridge. During this period, soldiers also received monetary allowances for the purchase of clothing, arms, and armor. By the late fourth century c.e. , the army came to include increased numbers of barbarians who had little need for armor and therefore little desire to purchase it for regular use. Instead, soldiers relied primarily on large circular shields for protection. When an army was on the march, its armor was carried in wagons and was normally used only during an actual pitched battle.

The Roman army also used various types of artillery both in battle and when conducting a siege. These included a device known as a Tormenta (Roman artillery)tormenta, which fired arrows, javelins, and rocks, as well as larger Ballistae ballistae and Catapults;Roman catapults that hurled larger arrows or stones.

During most of its history, the basic unit of the Roman army was the Legion (Roman formation)legion, which consisted only of Roman citizens and during the time of the early Empire numbered about 5,000 men. Each legion was organized into ten infantry Cohort (military unit)cohorts, one of which consisted of five centuries of 160 men each, while the remaining nine cohorts were each composed of six centuries of 80 men each. The Centuries (Roman formation)centuries were grouped into Maniple (Roman unit)maniples, each consisting of two centuries. During the first to third centuries c.e., each legion also included a cavalry detachment of 120 men. The command structure of the legion consisted of the fifty-nine Centurions, Romancenturions, who commanded the centuries; five Tribunes, Romantribunes, each of whom commanded two cohorts; a Prefectsprefect of the camp; a tribune of senatorial rank; and the legions’ commanders, the Legates (Roman)legates.

The legions were supported by units known as Auxilia (Roman contingent)auxilia, which consisted of troops recruited from subject peoples. These included infantry cohorts of 480 men divided into six centuries, and Cavalry;Romancavalry detachments Alae (Roman cavalry units)(alae) consisting of sixteen troops Turma (Roman army unit) (turmae) of thirty-two riders each. In the late first century c.e. these were enlarged to cohorts of ten centuries and alae composed of twenty-four turmae; the new cohorts and alae each theoretically numbered 1,000 men but were actually somewhat smaller in number. There were also mixed units, known as cohortes equitatae, consisting of one infantry cohort and four troops of cavalry, and units known as Numeri (Roman army units) numeri, which were not grouped as cohorts or alae but retained their own ethnic characteristics in terms of organization and weaponry. In addition to infantry and cavalry units, the auxilia included specialized troops such as archers and slingers.

Roman Empire, c. 117 c.e.

The early imperial army also included certain elite units based in Rome. The most important of these was the Praetorian Praetorian Guard (Roman elite unit)Guard, which was created by the emperor AugustusAugustus (Roman emperor)Augustus (63-14 b.c.e.) and originally consisted of nine cohorts. It supervised public life in the capital, escorted the emperor, and eventually came to play a major political role by occasionally helping to determine the succession to the imperial throne. The emperor was also protected by an elite personal cavalry unit known as the Equites (Roman cavalry unit)equites singulares Augusti. In the fourth century, the emperor Constantine the Constantine the GreatConstantine the Great (Byzantine emperor) Great (c. 275 to 285-337 c.e. ) disbanded both of these units because they had supported his rival Maxentius (died 312), and replaced them with a new bodyguard of German cavalry, the Scholae Palatinae scholae Palatinae.

In the late second and third centuries c.e., the imperial army underwent some notable changes. The emperor Lucius Septimius Severus, Lucius SeptimiusSeverus, Lucius SeptimiusSeverus (146-211 c.e.) increased both the pay and the size of the army, adding new auxilia units as well as three new legions. One of these was stationed near Rome, serving as a reserve unit and ensuring that Severus remained in power. In 212 c.e. Severus’s son, the emperor CaracallaCaracalla (Roman emperor)Caracalla (188-217 c.e.), extended Roman citizenship to most of the Empire’s population; this action essentially ended the distinction between legions and auxilia. At the start of the third century crisis (235-284 c.e.), the Empire lacked reserve forces that could deal with invasions by German tribes. As a result, the emperors of this period formed reserve field armies that could readily respond to such Barbarians;enemies of Romeinvaders. The cavalry of the early imperial army were essentially light cavalry, but by the fourth century the army included two types of heavily armored cavalry, known as Cataphracts (cavalry)cataphractarii and Clibanarii (Roman cavalry) clibanarii, which were modeled after Sarmatian and Persian cavalry respectively.

Roman Empire, c. 400 c.e.

In the fourth century, Constantine the Great established a single large mobile field army known as the Comitatus (Roman field army)comitatus. This was led by two newly created officers, the magister Magister peditum (Roman officer) peditum, who commanded the infantry, and the magister Magister equitum (Roman commander) equitum, the commander of the cavalry. Constantine thus established a clear division between the field army and the frontier troops, the Limitanei (frontier troops) limitanei, who during this period were organized into legions of 1,000 men. However, due to the inability of this single field army to respond to simultaneous attacks on various parts of the frontier, Constantine’s successors divided the comitatus into a number of regional field armies.

In the late fourth century, the Roman army faced mounting manpower shortages, which became particularly acute following a disastrous campaign against the Persians (363 c.e.) and a major defeat at Adrianople, Battle of (378 c.e.)Adrianople (378 c.e.). As a result, units of limitanei were transferred to the field armies. Moreover, the Romans permitted individual German tribes to settle within Roman territory as allies, or Foederatifoederati, who were obliged to provide military service to the emperor. However, the field armies fell into decline, and individual military commanders and other wealthy individuals consequently organized private armies known as Bucellarii (Roman private troops) bucellarii, which continued to exist after the fall of the western Roman Empire in 476 c.e.

During the early imperial period Roman leaders believed that it was Rome’s destiny to rule the entire world, a view that is reflected in book 6 of Virgil’s (70-19 b.c.e.) Aeneid (Vergil) Aeneid (c. 29-19 b.c.e. ; English translation, 1553). However, during this same period they came to recognize major factors that limited further territorial expansion. One of these was the sometimes formidable resistance by enemies such as the Caledonians, the Germanic tribes, and the Parthians and Sāsānians. Moreover, some territories open to conquest, such as the Arabian deserts to the far southeast, were of little economic or strategic value. Finally, the empire simply did not possess the military manpower or resources to expand indefinitely. Augustus stationed most of the legions on the frontiers and recommended to his successors the basic strategy of defending Rome’s existing frontiers rather than conquering additional territory.

Despite Augustus’s recommendation, emperors of the first to third centuries c.e. did not completely abandon the policy of Rome;expansionexpansion. Notable examples of this policy can be seen in the conquests of Britain, Dacia, and certain Middle Eastern territories, and in Septimius Severus’s campaigns in Mesopotamia and northern Britain. In addition, Roman emperors and their generals sometimes carried out Preemptive warfare;Romepreemptive attacks or reprisals in order to eliminate potential threats to the Empire. However, for the most part Roman emperors developed and adhered to a strategy of defense of the Empire’s frontiers. In doing so, they gradually established defensive zones, orLimes (Roman defensive zones)limes, along the frontiers. The central feature of such zones was a military road running along the actual frontier. At various intervals along such roads the Roads;RomanRomans built various defensive Fortifications;Romanfortifications, including large legionary camps, smaller forts, watchtowers, and fortified ports along rivers. In the first and second centuries emperors sometimes implemented a policy of “forward defense,” in which Roman forces took control of adjacent enemy territory and built roads, watchtowers, and forts in order to monitor enemy activity and discourage possible attack.

Sometimes the Romans built continuous defensive barriers in the limes in order to prevent barbarian entry into imperial territory as well as to define the Empire’s actual boundaries. These include three barriers built in the second century: Hadrian’s Hadrian’s Wall[Hadrians Wall]Walls;RomanWall and the Antonine Antonine WallWall in northern Britain, as well as a 240-mile-long wooden palisade built to protect the strategic area between the upper Rhine and Danube Rivers. Such fortifications consisted of a ditch, an embankment, and a rampart, with smaller forts and military camps of varying size built at intervals along the wall. A military road was built along the entire wall for the purposes of communication and moving troops in the event of an enemy threat.

During the early imperial period, frontier provinces were guarded by armies composed either of legions and auxilia or simply of auxilia cavalry and infantry units. The northern frontiers consisted of three regions: northern Britain;RomanBritain and the Rhine frontier (Rome)Rhine and Danube Danube frontiers (Rome)frontiers, each of which was threatened by warlike barbarian peoples. Rome’s eastern provinces lacked natural geographical barriers and were therefore vulnerable to attack from the Parthians;attacks on Roman Empire[Roman Empire]Parthians and, beginning in the third century, the Sāsānian Sāsānian Dynasty;attacks on Roman Empire[Roman Empire]Persians. During the reign of Augustus, the Rhine and North African Africa;and Romans[Romans]frontiers were considered the most dangerous in the Empire. However, as these frontiers were stabilized, their garrisons were reduced, and those on the Danube and eastern frontiers were gradually increased during the first to third centuries.

During the third century crisis, frontier defenses collapsed and emperors consequently developed a new strategy of imperial defense. During this period Germanic tribes and Sāsānian Barbarians;enemies of Romearmies frequently penetrated the limes and sometimes moved virtually at will within Roman territory. They sometimes posed a threat to cities located in interior areas away from the frontiers. The inhabitants of such cities consequently began to build defensive walls around them; in the late third century the emperor AurelianAurelian (Roman emperor)Aurelian (c. 215-275 c.e.) began construction of a wall around Rome itself. Moreover, third century emperors began to develop a strategy of “defense in depth,” which featured less emphasis on frontier forces and greater use of mobile field armies that centered on heavy cavalry units. Such armies were stationed in cities away from the frontier and then sent to intercept and defeat invaders. Moreover, in an attempt to deal with a shortage of manpower, some barbarians Laeti (barbarians)(laeti) were allowed to settle in Roman territory and entrusted with defense of part of the frontier; they were also required to provide recruits for the army.

In the fourth century, Constantine the Constantine the GreatConstantine the Great (Byzantine emperor)Great and his successors made increased use of mobile field armies. During this period, some emperors also attempted to strengthen the frontier defenses. Under DiocletianDiocletian (Roman emperor)Diocletian, frontier defenses were rebuilt, and new forts were built along the Danube and eastern frontiers and in North Africa. Valentinian Valentinian IValentinian I (Roman emperor)[Valentinian 01]I (321-375 c.e.) strengthened defenses on the Rhine and the Danube and directed Preemptive warfare;Romepreemptive attacks against barbarians along both frontiers. However, by the late fourth century the Empire was confronted with mounting manpower shortages as well as growing barbarian pressure on the frontiers. The manpower shortage resulted in understrength garrisons on the Rhine frontier being grouped together at a few vital points. In the fifth century c.e. Germanic invaders simply bypassed such strongpoints, which led to a complete collapse of the Rhine frontiers and, ultimately, to the end of the western Roman Empire.

The principal tactical objectives of a Roman commander were to move his army safely and swiftly and ultimately to defeat the enemy in open battle. A Roman army was most vulnerable when on the march, and therefore it had to be arranged in an order of march that would enable it to deal effectively with an enemy attack. Moreover, army commanders had to provide maximum protection for the baggage train because if enemy forces captured it and began looting, soldiers might break ranks in order to retrieve their belongings and consequently place the entire army in peril. In order to ensure safe and rapid passage through enemy territory, Roman troops often built roads and bridges. Moreover, at the end of each day’s march they built temporary marching camps for protection. These camps were surrounded by earthen ramparts and ditches and were disassembled the following morning before the army resumed its march.

When preparing for battle, Roman commanders sought to gather information about the enemy and to position the army in a manner best suited to the terrain on which it would fight. In battle, the Roman army was normally deployed in three parts, including a center or main body with flanking forces to its right and left that could be used to encircle the enemy. The legions were the most important component of the army. By the second century c.e. their basic battle formation was a solid phalanx consisting of several ranks of legionaries; however, the legion’s subdivisions of cohorts, maniples, and centuries gave it great flexibility in battle.

A Roman army normally began a battle with an artillery salvo designed to demoralize and disrupt the enemy. Next archers and slingers fired on the enemy, and the infantry hurled javelins. This was followed by a great shout from the Roman lines that was intended to frighten the enemy. If the enemy then fled, the Roman cavalry was sent in pursuit; the advance cavalry units moved rapidly to make sure that the enemy retreat was not a tactical deception, while the remaining cavalry advanced carefully in battle formation. If the enemy attacked, the front ranks of the legions held firm while other ranks hurled javelins, and archers fired arrows upon the attackers; the cavalry was sent to meet any enemy flank attacks. However, if the Roman army made the initial move, it directed its attack against the weakest point in the enemy position. Auxilia units carried out the initial assault. They were followed by the legions, who advanced in a Tortoise (Roman formation)“tortoise,” or Testudo (Roman formation)testudo, formation, with their shields locked together in the front, at the sides, and overhead in order to protect the legionaries from enemy javelins or arrows. After the enemy position was broken, hand-to-hand combat followed until the enemy either surrendered or fled. If the enemy did flee, Roman troops first searched the immediate surroundings to avoid falling into an ambush, and then the cavalry was sent in pursuit of the enemy.

When conducting Siege warfare;Romansieges of enemy fortresses or cities, Roman armies first set out to confine the enemy within their defenses by means of a series of fortified positions. The defenders were surrounded by a ditch and earthen rampart as well as a system of forts. Once this was constructed, the Romans set out to penetrate the enemy’s defenses and force them to surrender. In some cases, as in the Siege of Masada Masada, Siege of (70-73 c.e.)(73 c.e.), the Romans built a high approach platform or Rampsramp, which they would use to move a large siege tower close to the enemy wall. Archers positioned at the top of the tower could then fire on the defenders below; sometimes siege towers also were equipped with battering rams that were used to break through the enemy wall. Another method was to approach the enemy position under cover of a movable protective structure and then attempt to undermine the wall. If these methods did not work, the Romans would launch a frontal assault on the weakest point in the enemy defenses. This was preceded by a major artillery bombardment. The legionaries would then approach under cover of a testudo and scale the walls. After the top of the walls was secured, enemy cities were then sacked.

During the late imperial period, Roman warfare changed considerably. By the fourth century, most military action consisted of small-scale skirmishes involving small detachments of troops. However, in large-scale battles Roman commanders still sought to defeat barbarians such as the Goths by means of a decisive infantry clash in which the Roman infantry was deployed in a phalanx formation. When the enemy approached, they came under fire from archers deployed behind the phalanx; this might slow or even halt the enemy advance. If it did not, both sides would shout a battle cry, or Barritus (Roman battle cry)barritus, and the enemy would resume their advance. The Roman archery fire continued, while Roman infantrymen in the rear ranks hurled their javelins and moved forward to support the troops in the front ranks. After the enemy made contact with the Roman phalanx, the two sides pressed upon each other until one side lost heart and gave way. The cavalry then pursued the soldiers of the defeated army; it was in this last stage of battle that the largest number of casualties were inflicted.

Roman infantry employed the same tactics against enemy cavalry attacks. However, such attacks were relatively rare since it was difficult for cavalrymen to make their horses charge up against tightly packed infantry positions. If the infantry held firm, they could easily repel such attacks.

During the fifth century c.e., Cavalry;Romancavalry replaced infantry as the most important element in Roman armies. They generally used one of two different attack formations: a wedge, or rhomboid, formation, which was effective when carrying out elaborate maneuvers or seeking to pierce enemy formations, and a square, or oblong, formation, which was used when carrying out a full-scale charge. During the late imperial period, Roman cavalry used both skirmishing and shock tactics. In the former, the cavalry rode up to an enemy formation and fired their arrows; if the enemy held firm, they would fall back and attack again. If the enemy broke ranks, they then charged and engaged in close combat. FoederatiFoederati and other German cavalry in the late Roman army used shock tactics in which they simply charged, sometimes with the support of mounted archers, and attempted to defeat the enemy in close combat.

The noted Roman historian Cornelius Tacitus, CorneliusTacitus, Cornelius (Roman historian)Tacitus (c. 56-120 c.e.) wrote a number of works that offer valuable insights into early imperial warfare. These include a biography of his father-in-law, a governor of Britain, that describes Rome’s military campaigns in that province. Tacitus also wrote Ab Excessu Divi Augusti, also known as Annales (c. 116 c.e. ; Annals, Annals (Tacitus) 1598), an account of events in the Empire in the period from 14 to 68 c.e. , and the Historiae (c. 109; Histories, Histories (Tacitus) 1731) on the period from 68 to 96 c.e. , of which only the portions on the period from 69 to 70 c.e. have survived. The Jewish historian Flavius Josephus, FlaviusJosephus, Flavius Josephus (c. 37-c. 100 c.e. ) wrote a history of the Jewish revolt of 66-70, which includes descriptions of the Roman army in action.

Arrian ArrianArrian (Roman historian)(c. 89-155 c.e.), a governor of Cappadocia under the emperor Hadrian, wrote a firsthand account of a campaign that he conducted against the Alani in 134. He also wrote the Ars Ars Tactica (Arrian) Tactica, a manual on the training of cavalry. Pseudo-Hyginus, an obscure figure who probably lived during the second century c.e. , wrote De Munitionibus Castrorum (second century c.e. ; Fortifications of the Camp, 1993), a discussion of the planning and construction of Roman military camps. The fifth century Roman military theorist Flavius Vegetius Vegetius Renatus, FlaviusVegetius Renatus, Flavius Renatus wrote De Re Militari (383-450 c.e. ; The Fovre Bookes of Flauius Vegetius Renatus: Briefelye Contayninge a Plaine Forme and Perfect Knowledge of Martiall Policye, Feates of Chiualrie, and Vvhatsoeuver Pertayneth to Warre, 1572; also translated as Military Institutions of Vegetius, 1767), a treatise in which he called for a restoration of traditional military drill and training, and in doing so discussed various aspects of the Roman army in earlier periods.

Ammianus Ammianus MarcellinusAmmianus Marcellinus (Roman historian)Marcellinus (c. 330-395 c.e.), an officer who served in the Roman army in the 350’s and 360’s, wrote a history of the Roman Empire that continued Tacitus’s account from 96 to 378 c.e. However, only the books on the period from 353 to 378 c.e. have survived; these are a major source for political and military events of this period. The Notitia Dignitatum (c. 395 c.e. ) is an illustrated manuscript that lists the officers of the late fourth century army, as well as their units and where each was stationed.Rome;Empire

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Greek Warfare to Alexander

Greek and Hellenistic Warfare from Alexander to Rome

Carthaginian Warfare

Roman Warfare During the Republic

Celtic Warfare

Berber Warfare

Tribal Warfare in Central and Eastern Europe