Auxilia (“support”) were auxiliary forces in the Roman army. During the republics auxilia were constituted by allied armies, and their main task was supporting the Roman legions. The auxiliary troops were recruited from the inhabitants of Latin cities and allies (peregrini). With the conquest of Italy by Rome, other municipalities and cities of the Apennine Peninsula joined the community of arms with Rome. Members of these communes and cities were admitted to the community of arms with Rome on the basis of an agreement (feodus).
After the collapse of the Latin Union in the second half of the 4th century BCE Rome’s former allies were obliged and forced to provide military contingents. The number of these contingents corresponded to the number of allied forces. The allied troops were trained and armed according to the Roman pattern, which greatly facilitated their cooperation. Cities located on the coast were required to deploy a certain number of combat or transport ships with their crews. The normal quota of each commune from the territory of Italy was established by an agreement. In line with this, the consuls determined each year, after prior agreement with the senate, from which communes and in what number the quotas would be established. The overall strength of the auxilia contingent (established annually) was approximately four infantry legions made up of Roman citizens, while the cavalry of the allies was three times greater. The leader and the person responsible for financial management were established by the allied commune itself.
From the time of Octavian Augustus auxiliary troops alongside the legions became the second main formation of the Roman land forces. From their formation by Caesar to the victory of Octavian at Actium, they gained a prominent place in the army, especially thanks to their values demonstrated during the civil war. Octavian, having defeated his opponents’ armies and defeated his enemies, disbanded some of their auxiliary units and left the rest. Nevertheless, he was recruiting to new auxiliary units, which other emperors continued. It is very difficult to estimate the number of these divisions due to the constant changes in their organization.
With the conquest, auxilia were recruited only from provincial people who did not have Roman citizenship. The soldier serving in auxilia usually received Roman citizenship upon the termination of service, which has become the rule since Claudius. A certain danger revealed by the events at the turn of 69 and 70 CE in Germania and Gaul, was to keep auxiliary units close to the recruiting area and use locally-born officers. Soldiers in these units frequently deserted and acted to the disadvantage of the Roman army. For this purpose, troops were sent to the farthest part of the country, away from the recruitment site, to avoid similar situations. It was a reform of Emperor Vespasian. It was in force throughout the empire. Auxilia were to be stationed away from their home country, where there was recruitment, so as not to support their brethren in the event of revolts. People from quite distant towns were also mixed up. Vespasian deprived the troops of their native commanders and replaced them with Roman equites. These steps have proven to be very effective.
Auxilia were divided into cavalry squads, alae and infantry squads, cohortes. The cohortes was headed by the cohort prefect (prefectus cohortis), and alae, praefectus equitum was at the head. Under Emperor Claudius, this title was changed to prefectus alae. There were also mixed cohorts of infantry and cavalry (cohortes equitatae) introduced under Emperor Tiberius.
The ride usually consisted of 500 riders (alae quingenaria), but sometimes it consisted of 1000 riders (alae milaria), hence the distinction between them.
In the 2nd century CE they were divided into smaller units: alae quingenaria was divided into 16 turmae 32 people each, while alae milaria into 24 turmae 42 people each.
Walking cohorts (cohortes peditae) were organized in a similar way, and they were divided into centers. According to tradition, the names cohortes and turmaeauxilia come from cities and tribes subordinate to Rome. Hence the consistency of the appointed contingents of allied communes. It is not known whether the size of the individual cohorts and turmae were equal.
Under the emperor Nero or Vespasian, a new type of these units was created, known as milliariae, having almost twice as many soldiers as cohortes equitatae. For this reason, they have always served in strategically important places. As a result of the wars with the Parthians and the experience gained as a result of it, special units of heavy armoured cavalry auxiliary troops appeared in the Roman army, the so-called cataphractarii. In the third century CE In order to face the Persian cavalry, the so-called armoured cavalry, modelled on the Persian cavalry, was established. clibanarii.
Clibanarii was the last stage in the development of the Roman heavy cavalry. Completely armoured horsemen appeared in the Roman army from 69 CE when Vespasian took the Sarmatian cavalry on duty. The number of heavily armed cavalry increased in the 2nd century CE. Then Aurelian increased the numbers of this type of weapon around 275 CE, after failures in the fight against the rebellious Palmirian clibanarii. Again around 360 CE Constantine II increased their numbers. The clibanarius shown in the drawing was from around 275 CE. The reconstruction was based on the horse armour found in Dura Europos, on the descriptions of Ammian and Emperor Julian, who recorded that the rider was completely covered with a metal mask covering his head and face. This made the rider look like a “shining statue”. He further described the precisely made chain mail that covers the hands and joints. The limbs were protected by iron hoops. The body cover could have been a scale armour or it could have been made of rectangular iron plates connecting the chain mail.
The auxiliaries units were tasked with patrolling, repelling enemy attacks and other border protection tasks until the arrival of a regular Roman army stationed further from the border. During the battle, the auxiliary army supplied the legions with the same number of infantry and three times more cavalry. Allied forces were commanded by their own commanders, but the main command was 12 prefects (praefecti sociorum).
From each branch of the allied forces, a group of 1,600 pedestrians (pedites extraordinarii) and about 600 riders (equites extraordinarii) were separated, who were at the exclusive disposal of the commander-in-chief. The rest was divided into two groups, called wings (alae). They were placed on either side of the legions and their task was to keep the legion from being outflanked.
In the late empire, the divisions of auxilia included the Sarmatians (auxilia sarmatae), the Alans (auxilia allani), the Vandals and the Goths.
The strength of auxiliary troops during the principate period was probably at least the same as that of the proper army, ie about 150,000 soldiers.
The greatest honour for the auxiliary soldier was obtaining the title of citizen of Rome after 25 years of service in the legions. For this purpose, the so-called imperial decrees – tabulae honestae missionis (diplomata militaria ). Today, several hundred certified copies of imperial decrees are known, releasing auxiliary troops from military service (after a certain period of its duration) and granting them Roman citizenship, as well as for wives (not always) and children born earlier. This means that diplomata militaria was not issued for individual soldiers, but for entire units. The original text of the decree was written on large bronze tablets and displayed to the public in Rome on Capitoline Hill. None of such originals has survived to our times. For their own needs, the soldiers made copies of the entire general content of the document, and from the detailed part only the part that pertained to them personally. Such a copy consisted of two rectangular bronze plates, approx. 25 x 11 cm in size, with holes in the upper corners, enabling the plates to be joined with wire or metal rings. On both inner sides of such a diptych (a book of two cards), parallel to the long side of the plates, the entire text of the privilege was copied. After the whole was closed, a bronze wire was threaded through the centre of the plates, through specially made holes, and then sealed with wax seals, which were secured with brown capsules. The text of the privilege was repeated on one of the outer pages, and the names of seven witnesses confirming the credibility of the copy were posted on the other outer side.
From a legal point of view, the most important was the text inside the diptych. Such a document had to contain:
- imperial title fully developed;
- name of the unit (alae, cohortes) in which the soldier receiving the privilege was serving;
- the name of the province in which he served and the name of its viceroy;
- main text of the privilege;
- date of the decree (day, month, annual consular date);
- name of the detachment in which the holder of the copy served and the name of the commander;
- name of the holder of the copy, sometimes its origin (name of a tribe or territory), sometimes names of wife and children (up to about 140 CE);
- formula regarding the fact of making the write-off;
- on the outside of tablet II, names of seven witnesses.