List of Roman auxiliary regiments

Types of regiment

During most of the Principate era, until 212 CE, auxiliary regiments, called auxilia by the Romans, were formations kept separate from the legions, who were recruited from Roman citizens only. Auxilia were mostly recruited from the peregrini, the vast majority of subjects in the Roman empire who did not hold Roman citizenship. (in 212 CE, all the inhabitants of the empire were granted Roman citizenship).

There were three basic types of auxiliary regiment:

alae, which contained only cavalry and consisted nominally of 480 soldiers

cohortes peditatae or simply cohortes, which contained only infantry and consisted nominally of 480 soldiers

cohortes equitatae, which contained infantry with an attached cavalry contingent and consisted nominally of 600 soldiers, of which 480 were infantry and 120 were cavalry

A number of regiments, of all three types, were designated sagittariorum (sagitt), indicating that their members were equipped as archers. After about 80 CE, about 12 percent of regiments were enlarged from the quingenarie size and designated milliarie, which nominally consisted of 1000 soldiers, but in reality consisted of 720 soldiers, 800 soldiers, and 1040 soldiers respectively.

Contents of tables

Table I below lists auxiliary regiments during Hadrian's rule, for which there is the most comprehensive evidence. The table does not show regiments that were attested to in the 1st century but that, according to Holder, were dissolved by 117 CE, nor those that were probably founded after 138 CE. The precise number of regiments that existed during Hadrian's rule is disputed. The regiments are listed by the Roman province where they were deployed c. 130 CE.

Ethnic composition of regiments

The rule of the first emperor, Augustus, (30 BCE–14 CE) saw the foundation of the majority of the regiments attested in Hadrian's time. In the earlier part of this period, regiments were raised from and named after individual tribes, for example Campagonum, Trevirorum and Bessorum. Later, units were raised from and named after broad national groups, for example Hispanorum, Gallorum, and Thracum.

There is very little evidence concerning the organisation and policies of auxiliary recruitment. The ethnic origins of auxiliary recruits are attested in only a tiny fraction of cases. For example, the cohors II Gallorum veterana equitata must have recruited a calculated 8,000 soldiers over its probable lifespan of about 250 years but the origins of only two rankers are known. Conclusions about auxiliary recruitment drawn by scholars from the available evidence is regarded as tentative.

According to Holder, during the Julio-Claudian dynasty (14–68 CE), regimental ethnic identity was preserved to some extent, with evidence of continued recruitment from the original people. By the time of Hadrian, however, a regiment's name, in most cases, probably represented the ethnic origin of few, if any, of its members. This is because during the Flavian dynasty (69–96 CE), as a matter of deliberate policy, most regiments were deployed in provinces far from their original home and drew the majority of their recruits from local natives and the rest from all parts of the empire. In most cases, therefore, a regiment's name had become an identification tag devoid of ethnic significance. A regiment deployed long-term in the same province would thus, over time, acquire the ethnic character of its host population.

There are exceptions to this rule:

A minority of regiments remained stationed in their original home province, e.g., cohors I Delmatarum mill eq, still attested in Dalmatia in 130 CE.

Regiments founded a relatively short period before 130 CE, for example cohors I Aelia Dacorum which was stationed in Roman Britain in 130 CE would probably still have contained mostly Dacian recruits at this time, as it had been established by Hadrian only about a decade earlier.

Some specialised regiments, such as Syrian archers and the elite Batavi show some evidence of continued preferential recruitment from their original province.

Glossary

Some regiments were named after other people, for example ala Sulpicia after its first, or early, praefectus. In the Augustan era, commanders of auxiliary units were often Roman legionary centurions, or native chieftains. For example, ala Gallorum Atectorigiana was probably once commanded by a Gallic chieftain named Atectorix. Later, emperor Claudius restricted auxiliary commands to the lower aristocratic class of equites only.

Imperial dedications

Augusta

founded by emperor Augustus (r. 30 BCE–14 CE), or honoured with this title by any of his successors

Claudia

founded by, or honoured by, one of: Tiberius (r. 14–37 CE), Caligula (r. 37–41 CE), or Claudius (r. 41–54 CE), all of whom were members of the gens Claudia

Flavia

Vespasian (r. 69–79 CE) or one of his two sons and successors, Titus (r. 79–81 CE) or Domitian (r. 81–96 CE)

Ulpia

Trajan (r. 98–117 CE)

Aelia

Hadrian (r. 117–138 CE)

Aurelia

Marcus Aurelius (r. 161–180 CE)

Septimia

Septimius Severus (r. 197–211 CE)

In the 4th century, Valeria referred to emperor Diocletian (r. 284–305 CE) and Flavia to Constantine I (r. 312–337 CE) or some of his successors.

Raised during the Illyrian revolt

Names of regiments originally raised by emperor Augustus during the Illyrian revolt (6–9 CE) from Roman citizens unsuitable for service in legions, such as vagrants, convicted criminals, debtors, and emancipated slaves:

civium Romanorum

regiment originally composed of Roman citizens (including emancipated slaves)

ingenuorum

regiment originally composed of free-born (ingenui) Roman citizens

voluntariorum

regiment originally composed of volunteers (voluntarii), in reality slaves freed in return for military service during the Illyrian revolt

After their initial recruitment of Roman citizens, these regiments recruited non-citizens (peregrini) like all other regiments.

Other non-ethnic regimental names

classica

the regiment was originally recruited, probably during the Illyrian revolt, from naval personnel (from classis = "fleet"), who were mostly non-citizens

nauticarum

from nautae= "sailors"

maritima

praetoria

originally a cohort of the Praetorian Guard in Rome. Apparently a detachment of the cohort was left behind at the end of an imperial campaign, presumably to form the core of a new auxiliary cohort, retaining the prestigious name

singularium

ala formed around members of the elite equites singulares Augusti (imperial horseguards), left behind to reinforce frontier at the end of an imperial campaign

contariorum

specialised regiment of lancers (contarii) from contus (a long lance)

dromedariorum

specialised regiment of camel-mounted troops for desert warfare

Unit Epithets

Some regiment names included additional descriptors:

civium Romanorum (c.R.)

"of Roman citizens", honorific title awarded by the emperor to a regiment for valour. All current (but not future) members would be granted Roman citizenship, and the regiment would retain the title in perpetuity.

pia fidelis (p.f.)

veterana

uncertain meaning which may have been used to distinguish older unit from a newer unit with the same serial number and name

tironum

from tirones ("trainees")