The series of military defeats, civil wars, crop failures, epidemics, and other upheavals known as the crisis of the third century had a major impact on the entire Roman society, not least on the principle of recruitment, property, and social status of soldiers. At the very beginning of the third century AD. the emperor Caracalla granted the rights of Roman citizenship to all free residents of the state, which effectively destroyed the age-old division of the Roman army into auxiliary cohorts (auxiliaries), where provincials willingly served for the coveted rights of citizenship, and legions, whose service was much more profitable and prestigious, but was considered a privilege of Roman citizens. The reform of Caracalla removed the main motivation of service in the auxilia, and it ceased to exist in the form known in the time of the principate.
Formally, the call (dilectus) existed in the era of the principate, but in fact the authorities resorted to it only in a few cases, for example, before a major campaign of conquest or after heavy losses, as in the Marcomanian wars. However, Rome at the end of the third and beginning of the fourth century needed a much larger army than in the old days, and the principle of voluntary service could not physically meet the needs of the military machine. The population has declined significantly due to the Antonine plague and a series of civil wars, and with it the number of volunteers willing to serve in the army has decreased. In addition, a series of defeats suffered by the Roman army in the third century AD, combined with a drop in the purchasing power of soldiers ' salaries, made military service not very attractive in the eyes of the population. Therefore, the appeal, or conscription, came to the fore. Landowners were required to supply the army with a certain number of recruits, in proportion to the size and wealth of their land. In addition, since the time of Emperor Constantine, the sons of military men were also considered liable for military service, which made military service hereditary and served as a serviceable source of recruits.
However, even in the days of the dominant, military service carried a lot of benefits. All military personnel were provided with natural food, clothing and household items (annona), and their salaries (stipendium) were paid in gold solidi-coins that were practically not subject to inflation and had a reliable purchasing power. Salaries in solidi were a special privilege for military and civil servants of the state. In addition, military personnel received tax relief at the time of entry into service, and after five years of service, their wives were exempt from taxes (dominat soldiers were allowed to marry) and, depending on the status of the unit, their parents. Given that a large proportion of retired military personnel became owners of land, merchants or artisans, and the wives of soldiers often engaged in agriculture and crafts themselves, this created an additional incentive to send their sons and husbands to the army.
The tumultuous vicissitudes of the third century opened up many social elevators. The highest officer positions were now held by those from the equestrian class, but competent and successful commoners were also often promoted to the highest positions. The military reforms initiated by Diocletian and continued by Constantine created many new officer positions, and an ordinary soldier from the common people had every chance to become a centenary (analogous to a centurion), and then go on to become a commander of a separate part of the Roman army, whether it was a legion, cavalry ala or auxilia. In addition, even at the grassroots level, there were still profitable and promising positions, for example, in the znamenny group. Also, the specific privileges and size of a soldier's allowance depended on the prestige and status of the army unit where he served. The reform of Caracalla and the army's need for new, unknown or previously sparsely distributed branches of the armed forces, such as horse archers and super-heavy cavalry, led to the fact that service in legions or vexillations could be less prestigious and profitable than in auxiliaries. In short, the age-old division of the army into elite legions of citizens and auxiliaries of provincials disappeared forever.
Numerous third-century foreign invasions, revolts, and civil wars have built legions and auxiliaries with centuries of permanent home bases. Moreover, vexillationes (vexillationes), independent formations in 1-2 cohorts, were very often distinguished from the legion. There were a number of reasons for this. First, the army might need reinforcements in one area, but it didn't make sense to send an entire legion to it, exposing a large section of the border. Secondly, practice has shown that a compound of 1-2 cohorts of legionnaires with the support of auxilia can quite act independently and perform independent combat tasks. By the end of the third century A.D., many of these bills of exchange had effectively become independent units of the Roman army, maintaining only a formal connection with the legions from which they had been separated decades earlier.
The clear difference in the tactics and equipment of the legions and auxiliaries, characteristic of the principate, also disappears by the beginning of the IV century. All types of soldiers served in the legions, which sometimes left 1-2 cohorts, and in vexillations, and in foot auxiliaries, which will be described in detail below. However, finally, it is worth noting that the dominant is characterized by a high degree of unification of equipment elements of different types of troops. So, the set of a combat spearman (hastatus) turns into a set of an archer (saggitarius) by replacing the shield and spear with a bow and quiver with arrows, all other elements of equipment remain unchanged. Replacing the spear with javelins turns the spearman into a skirmisher (lancearius). Thus, the reconstruction of the dominant era is good because it allows you to create a lot of images without having to make most of the elements of the set again.
1) The Roman Army in the IV century. From Constantine to Theodosius. A.V. Bannikov
2) Armies of the Late Roman Empire. AD 284 to 476. History, Organization and Equipment. G. Esposito
3) De Re Militari, Publius Flavius Vegetius Renatus
4) Rerum Gestarum, Ammianus Marcellinus