Auxilia

Auxilia (Latin auxilia, "help" or "support troops") were the regular non-citizen units of the Roman army that served beside the legions under the Principate. If the legion was the core of citizen heavy infantry, the auxilia supplied what the legion often lacked: cavalry, archers, slingers, light infantry, scouts, local guides and garrisons for numerous frontier forts.

A soldier in such a unit is called an auxiliary. In the earlier period the word could describe many kinds of allied contingents, but after the reforms of Augustus the auxilia became a permanent professional system. Through them Rome drew peregrini, provincial elites and local military traditions into the army: Batavian cavalry, Syrian and Hamian archers, Thracians, Pannonians, Dalmatians, Spaniards, Numidians and many other groups.

From Republican Allies to the Army of the Principate

In the Roman Republic Rome did not rely only on its own citizens. Italian allies provided socii contingents, client kings supplied cavalry, archers or ships, and individual peoples retained their customary ways of fighting. After the Social War, most Italians became Roman citizens, and the old system of Italian allied troops lost much of its former meaning.

In the first century BC commanders increasingly used provincial and foreign detachments: Gallic, Germanic, Spanish, Thracian, Numidian, Cretan and eastern cavalry or missile troops. Under Augustus this practice was stabilised. The legions became citizen professional infantry, while the auxilia formed a parallel system of non-citizen units with long service, pay, officers, standards and fixed unit names.

This created the two-part army of the early Roman Empire. The legions supplied the politically prestigious core and heavy line, while the auxilia broadened the army's tactical range and held the provincial frontier. In numbers the auxiliary forces gradually equalled the legions or even outnumbered them in some provinces.

Types of Units

The main forms of the auxilia were established in the first and second centuries AD. Their names reflected size, troop type and origin:

• cohors peditata - an infantry auxiliary cohort, usually about 480 men in a quingenaria and more in a milliaria;
• ala - a cavalry unit divided into turmae, especially important for scouting, flanks and pursuit;
• cohors equitata - a mixed cohort combining infantry with a smaller mounted contingent;
• cohortes sagittariorum - archer cohorts, often associated with the eastern provinces;
• specialised units of slingers, scouts, sailors, guides, frontier troops or ethnic detachments.

Names such as Cohors I Hamiorum, Cohors I Pannoniorum, Cohors IV Delmatarum, Cohors IX Batavorum or Cohors II Cantabrorum do not always mean that the entire later unit was recruited only from one people. The name often preserved the memory of the original levy, while replacements increasingly came from the province where the unit was stationed.

Recruitment, Service and Citizenship

Most auxiliaries of the early empire were free non-citizens. For a provincial, service offered pay, food, a share of booty, the protection of a powerful institution and the possibility of rising above a local background. For Rome, it supplied needed military skills while tying provincial communities to imperial power.

A normal benchmark for service was twenty-five years. After honesta missio, honourable discharge, an auxiliary could receive Roman citizenship and conubium, the right to a legally recognised Roman marriage. These rights were recorded in bronze military diplomas: the text named the emperor, the unit, commanders, the veteran and the family covered by the privilege.

The auxilia were therefore not only a military institution, but also a mechanism of Romanisation. A soldier might be born outside the citizen body, spend decades on the Rhine, Danube, British or eastern frontier, and then become a veteran with a new legal status. After Caracalla's edict of AD 212, when most free inhabitants of the empire received citizenship, the old distinction weakened, but auxiliary units did not disappear at once: their forms changed gradually with the army of the third and fourth centuries.

Battlefield Role

The auxilia should not be reduced to "weak" infantry beside the legions. Their role depended on the unit type. Infantry cohorts could hold a sector of the line, guard a fort, escort baggage, build roads and take part in sieges. Light infantry operated ahead of the main line, harassed the enemy with javelins and withdrew behind denser formations. Archers and slingers struck men, horses and exposed parts of an enemy formation at range.

Auxiliary cavalry performed tasks for which legionary infantry was unsuited: reconnaissance, flank protection, sudden raids, pursuit of a fleeing enemy, communication between columns and rapid response to threats. On the frontiers, alae and mixed cohorts were often the first forces to meet raids and check movement beyond the fort line.

In major campaigns the auxilia and legions worked as one system. A legion supplied heavy infantry mass, engineers and siege work, but without cavalry, missile troops, guides and provincial garrisons the army would have been far less flexible.

Equipment and Appearance

Auxiliary equipment was not a single uniform for the whole empire. Early images and finds show oval or round shields, spears, javelins, swords, daggers, bows, scale or mail armour, and sometimes no body armour. In the cavalry, the long sword, spear, horse harness, saddle, spurs and protective fittings for rider or horse became especially important.

The difference from a legionary did not rest on one object. A legionary is more often associated with the large scutum, pilum and heavy infantry line, but Roman equipment changed constantly by period and region. Auxiliaries could use the clipeus, parma, hasta, javelins, gladius, spatha, pugio, mail armour or scale armour in different combinations.

Auxiliary Infantry D helmets, reliefs from Mainz, tombstones from Rhine and British garrisons and images on Trajan's Column show not one canonical appearance, but a range of solutions. A first-century auxiliary, an archer from an eastern cohort, a Batavian horseman and a late Roman cavalryman should therefore not look the same.

Forts, Frontiers and Daily Life

On the imperial frontiers, the auxilia often lived not beside a legion, but in their own forts. Such forts were smaller than legionary fortresses, yet they had gates, headquarters, barracks, granaries, workshops, a bathhouse and a civilian vicus nearby. In Britain, on the Rhine and on the Danube, auxiliary garrisons controlled roads, crossings, pasture, tax collection, merchants' movement and local conflicts on a daily basis.

This environment is especially visible on Hadrian's Wall and at Vindolanda. The Vindolanda tablets name commanders, soldiers, slaves, families, supply requests, festivals, letters and household affairs. They show that an auxiliary unit was not only a battle formation: scribes, craftspeople, women, children, traders and local intermediaries existed around it.

Auxiliary units were also a major channel of cultural exchange. Eastern archers could serve in Britain, Batavians on the continent and overseas, Thracians or Pannonians far from their homelands. Names on tombstones, dedications to local and Roman gods, military diplomas and everyday objects show people who both preserved origins and entered the Roman military system.

Command and Internal Organisation

Auxiliary commanders usually belonged to the equestrian order. An infantry cohort was commanded by a praefectus cohortis, an ala by a praefectus alae; large milliaria units could have a tribune. Beneath them stood centurions in infantry, decurions in cavalry, optiones, standard-bearers, trumpeters and junior specialists. In a cavalry ala the main small unit was the turma.

This command system tied local recruitment to Roman discipline. A unit name could be provincial or ethnic, but pay records, orders, guard duty, construction, personnel lists and rewards belonged to a common military administration. The auxilia therefore preserved diversity while becoming part of a single imperial army.

Chronology

• 3rd-1st centuries BC - Rome uses allied and client contingents: Italian socii, Numidian cavalry, Cretan archers, Spaniards, Gauls and other troops.
• 91-88 BC - the Social War changes the status of the Italians; the old model of Italian allied troops loses its former shape.
• Late 1st century BC - Augustus creates a stable system of professional auxilia beside the legions.
• 1st century AD - many cohorts and alae with ethnic or provincial names are formed and moved between provinces.
• AD 69-70 - the Batavian revolt shows both the strength and the danger of provincial military networks.
• 2nd century AD - the auxilia become central to garrison life on the limes, especially in Britain, on the Rhine and on the Danube.
• AD 212 - Caracalla's edict weakens the distinction between citizens and peregrini, but does not abolish auxiliary units.
• 3rd-4th centuries AD - the old auxiliary system gradually dissolves into new forms of the late Roman army.

Related Topics

• Roman Army
• Legion
• Cohort
• Ala
• Auxiliary Spearman
• Auxiliary Skirmisher
• Auxiliary Cavalryman
• Sagittarius
• Cohors IX Batavorum
• Cohors II Cantabrorum
• Peregrini
• Roman Citizenship

Literature

• Cheesman G. L. The Auxilia of the Roman Imperial Army. Oxford: Clarendon Press, 1914.
• Haynes I. Blood of the Provinces: The Roman Auxilia and the Making of Provincial Society from Augustus to the Severans. Oxford University Press, 2013.
• Holder P. A. Studies in the Auxilia of the Roman Army from Augustus to Trajan. BAR International Series 70. Oxford, 1980.
• Spaul J. E. H. Cohors 2: The Evidence for and a Short History of the Auxiliary Infantry Units of the Imperial Roman Army. BAR International Series 841. Oxford, 2000.
• Spaul J. E. H. Ala2: The Auxiliary Cavalry Units of the Pre-Diocletianic Imperial Roman Army. Andover, 1994.
• Goldsworthy A. K. The Roman Army at War 100 BC-AD 200. Oxford, 1996.
• Bishop M. C., Coulston J. C. N. Roman Military Equipment: From the Punic Wars to the Fall of Rome. Oxford, 2006.
• Roman Inscriptions of Britain; Vindolanda Tablets Online; Roman Military Diplomas.