One of the most successful and long-lived armies of antiquity, it developed standards of discipline, organization, and efficiency that would not be seen again in western Europe until the late 17th century. It began as the small warbands of aristocratic war leaders, but by the end of the 6th century bc it had developed into a phalanx of heavily armoured hoplites fighting in dense array and carrying round shields. The core of the army was composed of all citizens with the property to pay for a panoply. Poorer citizens served as light infantry or servants. As in Greece, the army was designed for short campaigns in the less busy periods of the agricultural year.
By the late 4th and early 3rd centuries bc, the army began to assume the familiar form of the manipular legion. This was described in its classic form by the Greek historian Polybius, writing in the 2nd century. Each legion consisted normally of 4, 200 infantry and 300 cavalry, but in times of emergency this could be increased to 5, 000 infantry. Its main strength was the heavy infantry, divided into three lines (the triplex acies) each of ten maniples. The first and second lines, the hastati and principes respectively, each consisted of 1, 200 men armed with two heavy javelins, or pila, while the third line, the triarii, mustered 600 spearmen. Recruitment to the heavy infantry was based on property qualification and membership of each line on age and experience, the triarii consisting of veterans. All heavy infantrymen wore body armour, ranging from a mail corselet to a simple disc-shaped chest protector, carried the oval, semi-cylindrical body shield (scutum), and used the short thrusting sword (gladius). In support were 1, 200 light infantry or velites, armed with a bundle of light throwing spears and a round shield. Maniples were commanded by centurions and deployed in a chequerboard formation (quincunx) so that the maniples in the second line covered the intervals between those in the first, while the third line covered the gaps in the second. The legion was commanded by six tribunes. Each of the two consuls, the annually elected senior magistrates of the Roman republic, were normally given command of two legions and a similar number of allied troops, divided into two wings (alae) with 4, 000-5, 000 infantry and 900 cavalry. The pick of allied troops, about one third of their overall number, were formed into the cohorts of extraordinarii, kept at the immediate disposal of the consul.
Consular armies of two legions plus allies fought most of the wars in the 3rd and 2nd centuries bc, finally beating Hannibal and crushing the armies of the Hellenistic kingdoms. Sometimes the armies of both consuls were concentrated, in which case the consuls commanded on alternate days. The manipular legion proved very effective in fighting pitched battles. Armies moved rapidly into contact, but then spent days or weeks close to the enemy, jockeying for a favourable position. Another characteristic was the great care taken to build a highly ordered camp every night, giving it a secure base for this manoeuvring. In battle the manipular formation proved far more flexible than the rigid phalanx still employed by Hellenistic pikemen.
Prolonged campaigning against Spanish and Gallic tribal armies probably provided the impetus for the next major reform of the Roman army. Traditionally associated with Marius, the changes are now thought to have been more gradual, reaching fruition near the end of the 2nd century bc. A citizen militia was unsuitable for long service as garrisons in the provinces, so increasingly the army came to consist of professional soldiers, men drawn from the classes lacking the minimum property qualification formerly required for service. Dependent on their commanders during their service and upon retirement, this broke the allegiance of the army to the Roman state that had previously been such a source of political stability.
After the Social and Civil Wars and the extension of Roman citizenship to most of Italy the allied alae vanished and all Italians were henceforth recruited into identically armed and organized legions. When the property qualification was abandoned, so were the distinctions of equipment within the legion. The velites disappeared and all legionaries were now heavy infantrymen, armed with the pilum. The basic subunit of the legion became its ten cohorts of 480 men each, composed of one maniple from each of the three lines, each divided into two centuries of 80 men commanded by a centurion.
The legion of ten cohorts was more flexible than the manipular legion. As adept at fighting pitched battles, its structure allowed it to operate effectively in the smaller scale fighting common against the politically disunited tribes of the western empire. The growth of professionalism and permanence of units improved the army's overall quality and in particular its abilities in specialist tasks such as engineering and siegecraft. These were the armies with which Caesar and Pompey added vast territories to the empire. They were also the armies which they and other commanders turned against each other in the civil wars which destroyed the republic and led to the establishment of a principate under Caesar's adopted son, Augustus.
The army of the principate was shaped in the period from Augustus to Claudius, building on the developments of the last centuries. Legions became permanent units with their own numbers and names and many were to remain in existence for centuries. Each consisted of ten cohorts of 480 men in six centuries of 80, each commanded by a centurion, and a small cavalry force of 120 riders. At some periods, some legions had a larger first cohort of 800 men in five centuries. Legions included large numbers of specialist personnel, ranging from armourers to administrators, catapult crewmen to engineers. Soldiers were Roman citizens who served for 25 years, the last five with the veterans who were exempt from most duties. Each legion was commanded by a legate supported by a senior tribune, Roman aristocrats whose career included a range of both civilian and military tasks and who served with a legion for a few years. Greater continuity and professionalism was provided by the corps of centurions, some of whom were promoted from the ranks. Supporting the legions were the non-citizen troops of the auxilia. The infantry were organized into cohorts of 480 or 800 men, the cavalry in alae of 512 or 768. There were also units (corhortes equitatae) composed of a mixture of infantry and cavalry. The auxilia included units of archers and light troops, but most seem to have been equipped with mail armour, helmet, and shield and armed with a sword and various types of spear/javelin. At the end of their 25 years' service these auxiliaries were granted citizenship.
The army's strategy and tactics were highly aggressive, attempting to seize and maintain the initiative in any conflict. It was also flexible enough to adapt to the local situation. This, combined with the usually high quality of its units and sound logistical support, gave the army an advantage over all its opponents. The army of the principate remained in essentially this form until the 3rd century ad. Many of the details of the organization of the later Roman army are now obscure. More units were created, but the units themselves seem to have been much smaller, legions perhaps being reduced to as little as 1, 000 men. There was also a move away from deploying almost all of the army in the frontier provinces as had been the practice throughout the principate. This culminated in the division between the troops deployed on the frontiers (limitanei), and the units of the field armies (comitatenses). The comitatenses were not involved in local policing and administration and so were not tied to one region. They formed central reserves against both external threats and political rivals from within the empire.
The units of the later Roman army were potentially as efficient as they had ever been, but political weakness often made it harder to muster and supply a large army in the field. The army still won most of the battles it fought, but its doctrine had become less confident, less aggressive, and increasingly reluctant to risk open battle. Considerable use was made of foreign troops fighting under their own leaders, and traditionally it has been assumed that the barbarization of the army led to decline in quality, but this is now fiercely debated. Even so, the Roman army in the west disappeared in the 5th century when the political and economic infrastructure to support it collapsed, not as a result of military defeat.
Bibliography
- Elton, Hugh, Warfare in Roman Europe ad 350-425 (Oxford, 1996).
- Goldsworthy, Adrian, The Roman Army at War 100 bc-ad 200 (Oxford, 1996).
- Keppie, Lawrence, The Making of the Roman Army (London, 1984).
- Webster, Graham, The Roman Imperial Army (London, 1985)
— Adrian K. Goldsworthy
