List of Roman army unit types

This is a list of unit types and ranks of the Roman army from the Roman Republic to the fall of the Roman Empire. This includes a list of the sub-units of the Roman Legion.

The list below covers mainly unit types of the Roman Empire, since the early Roman army was from surviving records more uniform. Likewise, there is a greater concentration on legionary ranks, since there are greater records extant than for auxiliary and other non-legionary units.

More than one term was often used to describe essentially the same rank or unit type and, additionally, several words could be strung together to more exactly describe a man's unit or rank - for instance a "discens immunis veterinarius" would be a trainee military veterinarian.

Comments added include period when such units existed, cause of disappearance (if relevant), and brief summary of role, as well as link to the main article (if existing).

Unit types

• Accensus - either a public officer who attended on several of the Roman magistrates; or a kind of supernumerary soldier who served to fill the places of those who were killed or disabled by their wounds in the Roman Republic
• Adscripticius - a supernumerary soldier of the Roman Republic who served to fill the places of those who were killed or disabled by their wounds.
• Antesignani - Vanguard troops. Antesignani means "those before the standard" (Signus, Signum)
• auxilia - troops in the Roman army of the late Republican and Imperial periods who originally stayed in their home province but were formalised and later took on the role of providing specialist support to the legions. An example would be the Syrian archer.
• Balearic slingers - Expert slingers from the Balearic Islands off the Mediterranean coast of modern Spain.
• bucelarii - a unit of soldiers in the late Roman and Byzantine empire, that were not supported by the state but rather by some individual such as a general or governor.
• cataphractarii - heavily armed and armoured cavalrymen, adopted from the Parthians and first deployed by the Romans in the 2nd Century AD during the reign of emperor Hadrian.
• Classiarii - naval infantry
• Celeres - a force of 300-500 probably cavalry that served as a bodyguard to the early Roman kings. Their name Celer is Latin for "swift".
• Clibanarii - a military unit of heavy armoured horsemen similar to the Cataphracti
• Cohortes urbanae - a police unit of urban Rome and sometime counterbalance to the power of the praetorian guard.
• Comitatenses - the standard legionary soldier after the reforms of Constantine
• Comitatenses Palatini or Auxilia Palatini- a central field army of the late Roman Empire that was unique in that it was always under the direct command of the Roman Emperor
• Contarií - cavalry equipped with the contos (kontos), a very long lance
• dromedarii - camel riding auxiliary forces recruited in the desert provinces of the east Roman republic
• Duplicarius - officer in the army
• Equites - Roman citizen horse troops drawn from the Roman equestrian class.
• Foederati - soldiers provided by barbarian tribes in return for subsidies
• frumentarii - the secret service of the Roman Empire.
• Hastati - the first line of battle in the Roman Republican Army.
• herculiani - the imperial guard of the Emperors of the Roman Empire from 284 until 988
• Ioviani (also called Jovians) - the imperial guard of the Emperors of the Roman Empire from 284 until 988
• Lancearii - Spear armed mail clad field troopers that supported the comitatenses
• Latini - allied troops of the Republic provided by non-citizens living in allied Latin towns
• Limitanei- Lighter late legionaries similar to the auxilia of Caesar's day normally use in garrison.
• Menapian spearmen - More few and at best auxiliary mercenaries.
• Nabataean archers - Auxiliary bowmen recruited from Nabataea, in what is now southern Jordan.
• Numerii - A loose term for any soldier
• pedites - the infantry of the early army of the Roman kingdom. The majority of the army in this period.
• Peditatus - a term referring to any infantryman in the Roman Empire
• praetorians - a special force of bodyguards used by Roman Emperors
• Principes - the second line of battle in the Roman Republican Army. They were also chieftains in Briton like Dumnorix of the Regneses (he was killed by Gaius Salvius Liberalis' soldiers)
• Rorarii - the final line, or reserve, in the ancient pre-Marius Roman army. These were removed even before the reforms as the Triarii provided a very sturdy anchor
• Sagittarii - archers, including horse-riding auxiliary archers recruited mainly in the Eastern Empire and Africa
• Scholae Palatinae - an elite troop of soldiers in the Roman army created by the Emperor Constantine the Great to provide personal protection of the Emperor and his immediate family
• Socii - Conscripts
• speculatores - the scouts and reconnaissance element of the Roman army
• supernumerarii - a kind of supernumerary soldier who served to fill the places of those who were killed or disabled by their wounds
• Triarii - the third standard line of infantry of the Roman Republic's army
• Velites - a class of light infantry in the army of the Roman Republic
• Vigiles - the firefighters and police of Ancient Rome

Military ranks

• Accensus - a reservist or light legionary infantry soldier.
• Acceptarius - a discharged soldier.
• Actarius - a military or camp clerk.
• Adiutor- a camp or headquarters adjutant or assistant.
• Aenator - military musician such as a bugler.
• Agrimensor - a surveyor (a type of immunes).
• Aquilifer - carried the legionary eagle.
• Alaris - a cavalryman serving in an ala.
• Architecti - an engineer or artillery constructor.
• Armicustos - a soldier tasked with the administration and supply of weapons and equipment. A quartermaster.
• Ballistarius - an artillery operator.
• Beneficiarius - a soldier performing an extraordinary task such as military policing or a special assignment.
• Bucinator - a trumpeteer or bugler.
• Cacula - an un-enlisted camp servant
• Capsarior - a medical orderly.
• Causarius - a soldier discharged for wounds or other medical reasons.
• Centurion - officer rank, generally one per century, in charge of century.
• Clinicus - a medic.
• Cornicen - bugler
• Doctor - a trainer, subdivisions for everything from weapons to hornblowing
• Draconarius - Roman cavalry standard bearer
• Decurion - leads a troop of cavalry (14-30 men). Often confused with decanus.
• Decanus - leads a contubernium (a legionary tent group of 8 men)
• Discens - Miles in training for an immunis position.
• Dux - a general in charge of two or more legions
• Evocatus - soldiers in the Roman army, who had served out their time and obtained their discharge (missio), but had voluntarily enlisted again at the invitation of the consul or other commander
• Hastatus Prior - a centurion commanding a manipulus of hastati. A high ranking officer within a manipuli
• Hastatus Posterior - a deputy to the hastatus prior
• Hastiliarius - a weapons instructor.
• Imaginifer - A standard-bearer carrying the imago - the standard which bore a likeness of the emperor, and, at later dates, his family.
• Immunes - those soldiers of the military of ancient Rome who were "immune" from combat duty and fatigues through having a more specialist role within the army
• Legatus - general in the Roman army; literally the "deputy" of the emperor, who was the titular commander-in-chief
• Legionary - the heavy infantry that was the basic military unit of the ancient Roman army in the period of the late Roman Republic and the Roman Empire
• Medicus - physician or combat medic. Specializations included surgery (medicus vulnerarius), ophthalmology (medicus ocularius) and even veterinary (medicus veterinarius). At least some held rank equivalent to a centurion.
• miles or Miles Gregarius - The basic private level foot soldier
• Optio - One per century as second-in-command to the centurion. Could also fill several other specialized roles on an ad hoc basis.
• Pilus Prior - The commander of the first century of each cohort.
• Pilus Posterior - Deputy to the pilus prior
• Praefectus Castrorum - camp prefect, third-in-command of the legion, also responsible for maintaining the camp, equipment and supplies. Usually a former primus pilus.
• Primus Pilus - (literally 'first file', not spear) the commanding centurion of the first cohort and the senior centurion of the entire Legion
• Princeps Prior - a centurion commanding a manipulus of principes
• Princeps Posterior - a deputy to the princeps prior
• Principales - a group of ranks, including aquilifer, signifer, optio and tesserarius. Similar to modern NCOs.
• Protectores Augusti Nostri (aka Protectores Divini Lateris) honorific title for senior officers singled out for their loyalty to the Emperor and soldierly qualities. Constitute an Order of Honour rather than a military unit. First appears in mid-Third Century AD
• Quaestionarius - an interrogator or torturer.
• Retentus - a soldier kept in service after serving required term
• Salararius - a soldier enjoying special service conditions or hired as a mercenary.
• Scorpionarius - an artilleryman operating a scorpio (dart-thrower) artillery piece
• Signifer- Standard bearer of the Roman Legion
• Tablifer - A guard cavalry standard-bearer
• Tesserarius - guard commander, one per century
• Tribuni militum angusticlavii or military tribune -
• Tribunus militum laticlavius - military tribune of senatorial rank. Second in command of a legion. Appointments to this rank seem to have ceased during the sole reign of Gallienus as part of a policy of excluding senators from military commands.
• Venator - a hunter (a type of immunes)
• Vexillarius - a standard-bearer (carried the Vexillum)

The three main ranks are the Hastati, The Principes, and The Triari.

Sub-Units of the Roman legion

In the years following the reforms of Gaius Marius in 107 BC the organisation of the legions became standardised as follows:

• Contubernium - The smallest organized unit of soldiers in the Roman Army. It was composed of eight legionaries led by a non-commissioned officer called a decanus. Ten contubernia formed a centuria.
• Centuria - A centuria consisted of 80 men under the command of a Centurion and his Optio. Six centuria formed a cohort.
• Cohort - A cohort consisted of 480 men. The most senior ranking centurion of the six centuria commanded the entire cohort.
• First Cohort - The first cohort was a double strength cohort (consisting of five double-strength centuria). The centurion of its first centuria, the Primus Pilus, commanded the first cohort and was also the most senior Centurion in the legion.
• Legion - A legion was composed of nine cohorts and one first cohort. The legions overall commander was the Legatus legionis, assisted by the Praefectus castrorum and other senior officers.
• Vexillation - These were temporary task forces composed of one or multiple centuria detached from the legion for a specific purpose. Vexillations were under the command of an officer appointed by the Legatus.