The word "legion" comes from "legio," meaning a levy, hearkening back to the days of the Republic and its conscript armies. The professional legions of the principate however, were both astonishingly modern and quintessentially Roman in their recruitment, organization, and training.

Recruitment and Training

A dilectator, or recruiting officer, would recruit candidates to stand before the probatio, or recruiting board. Vegetius informs us that a candidate for the legions was given a thorough physical, and was required to be a minimum of five feet, five inches tall (in Roman measurements: five feet, ten inches tall), with a good bearing and muscular build (3). However, height was a desired, as opposed to mandatory, trait, and if all other characteristics were considered satisfactory, height could be waived. While Vegetius focused heavily on the physical characteristics of the recruits, the Roman patronage system cannot go unmentioned. Patronage in Rome was considered an essential element of Roman political and social life, and a recommendation from a person of import, whether a relative or patron, heavily influenced a recruit's chance to be accepted into the legions. Moreover, the higher the social status of the family of the candidate, the higher he was likely to begin in the legion hierarchy (Bohec 72-74). Hence the son of a patrician or equestrian would begin as a tribune, while the son of a centurion could hope for acceptance into the centuriate. A cives (Roman citizen) was allowed to enter the legions while a peregrini (non-citizen) was directed toward the auxilia.
Once accepted, the new tiro was sent off to training. The Romans regarded training as an absolute necessity in the preparation for war. They did not consider warriors to be born, but made, and their intense training programs reflected this. When available, an evocatus controlled all training, ably assisted by a number of training specialists, including the armatura or doctor armorum, who taught swordplay. Even the instructors had a trainer: the discens armaturarum (Bohec 112-112). From the very beginning, a tiro was drilled relentlessly, both to strengthen him physically, and to acquaint him with the tools of war. Once he had acquired sufficient proficiency with his individual weapons, he joined in the various unit level exercises, which ranged from civil engineering to actual battle drills (Bohec 110). The skill of marching in step was emphasized, as was swimming and road marching. Soldiers habitually trained with double weight weapons to build endurance and speed, and the men were taught to thrust with their blades, not to strike with the edge. The thrust was considered more deadly, inflicting lethal wounds in the vitals, and Vegetius remarks that the Romans "made a jest of those who fought with the edge of that [the sword] weapon" (5). Josephus, in "The Wars of the Jews," provides us with one perspective on how Roman training was perceived by other cultures:

". . . for they do not begin to use their weapons first in time of war, nor do they then put their hands first into motion . . . they have never any truce from warlike exercises . . . for their military exercises differ not at all from the real use of their arms . . . nor would he be mistaken that should call those their exercises bloodless battles, and their battles bloody exercises." (Josephus V, 70)

It is easy to see how the Roman war machine would overawe a people less dedicated to the science of warfare.


The smallest unit in a legion was the century, which consisted of roughly 80 men. A century was subdivided into ten sections of eight men (referred to as a contubernia), sharing a tent and mule in the field. While in Republican times the base maneuver element was the maniple (composed of two centuries), by the principate the maniple had been replaced by the cohort. A cohort was composed of six centuries, and ten cohorts formed a legion. The first cohort was milliary, meaning it had five double centuries as opposed to the six standard centuries of the remaining cohorts, giving the legion a strength of roughly 5100 men (Webster 109-110). Each Legion also had a small cavalry force attached to it, which Josephus listed as 120 in number (III, 6). These mounted trooops were not assigned to the legion as a whole, but rather to individual centuries, and were thus commanded by centurions. They were not used as cavalry (this was the function of the attached alae); instead they formed a mounted force of scouts and dispatch riders.

Legionary Officers

The legion commander was the legatus legionis, the representative of the Emperor, to whom a portion of the princeps' imperium had been delegated. The position of the legatus fulfilled a necessary step on the cursus honorum, the sequence of positions a Roman nobleman filled as he advanced through his political career. Typically, the legatus would remain in this role for only a few years before moving on to another position. Assisting the legatus were six tribuni militi, or military tribunes. The senior of the tribunes was normally a tribunus laticlavius (of senatorial rank and thus entitled to the broad purple stripe on his toga), a senator delegate working his way up the cursus honorum. The remaining tribunes were of equestrian rank and designated as tribuni angusticlavii (wearing a toga with a narrow stripe). Finally, the last equestrian officer was the praefectus castrorum, responsible for the maintenance, supplies, and equipment. The praefectus castrorum was third in command, and had risen through the centuriate to become a primus pilus, or senior centurion. While this was normally the height of a primipilares' career, they could rise to even greater rank as procurators of provinces-or, if fortunate, enter the Praetorian Guard (Webster 113). It should be noted that, while competence certainly played a role in promotion and advancement, social status played at least as large a part. Men were selected as tribunes based upon their social standing in society and the power of their patrons; there was no competitive "academy" such as we have today. Although we consider such patronage a sign of corruption today, the Romans believed this was the natural order of things. The Roman system certainly produced its share of inept commanders and officers, but it must be stressed that it also produced many exceptional ones as well-and while the commander and many of his officers rotated in and out of positions, they could always fall back upon the institutional continuity of the legions: the centurions.

Legionary Officers
legatus legionis
tribunus laticlavius
praefectus castrorum
tribunus angusticlaviustribunus angusticlavius tribunus angusticlaviustribunus angusticlavius tribunus angusticlavius

The Centuriate

The centuriate was the backbone of the legions. Each century was commanded by a centurion, and the legion had a total of sixty of these vital leaders. The centurions were ranked by seniority, with the commander of the first century of the first cohort titled the primuspilus. This post was held for only one year, allowing it to rotate among the most senior, and outstanding, centurions (Webster 114). The primipilates was a highly coveted position, well paid and accompanied by a hefty retirement bonus-sufficient wealth to move the centurion and his family into the ranks of the equestrians. The primipilates was also a stepping-stone to greater advancement in civil and provincial positions. Second in seniority was the princeps prior, who trained and led the headquarters personnel. The remaining centurions of the first cohort were, in descending order of seniority, the hastatus, princeps posterior, and hastatus posterior. In the remaining cohorts the command structure was less rigid, with the centurions of roughly equal status (Bohec 44). The titles of these men, pilus prior, pilus posterior, princeps prior, princeps posterior, hastatus prior, and hastatus posterior, were remnants of the Republican manipular-based legion and its triple battle lines (Keppie 174).

Centurion Organization Within the Cohort
1st Maniple2nd Maniple3rd Maniple4th Maniple 5th Maniple6th Maniple
1st Cohortprimus pilusprinceps priorhastatus prior princeps posteriorhastatus posterior
2nd-10th Cohortspilus priorprinceps prior hastatus priorpilus posteriorprinceps posterior hastatus posterior

Within the rank structure of the centuries there were four positions between the centurion and the common legionary: the signifer, optio, tesserarius, and custus armorum (Webster 117). The signifer and optio were each paid double wages (and were therefore called "principales"), with the signifer carrying the century's standard in combat and handling all of its paperwork in garrison. The optio commanded the century in the absence of the centurion. Below these positions were the tesserarius and custus armorum. The tesserarius was responsible for assigning the daily challenge and password, organizing sentries, and conducting inspections of the guards. The custus armorum was the century's armorer, responsible for weapons and equipment. Outside of the centuries, but below the centuriate, were numerous positions that were integrated into the legions staff in a complex weave. Among the most important were the aquilifer (who carried the legionary eagle), and the imaginifer (who carried the image of the emperor). The aquilifer was also in charge of the legion's war chest, from which the legion was paid.

The Immunes

Perhaps the most difficult positions to categorize were the immunes. The legion had no separate engineering or other specialty corps; instead there were a large number of men who were granted dispensation-immunity-from the various unpleasant physical duties a legionary could be assigned (Webster 118). This dispensation was a significant benefit, as the centurions were accustomed to receive bribes from soldiers seeking to avoid such tasks. The array of immunis positions is staggering, ranging from the agrimensores (surveyors), to the sagittarii (arrow makers), and extending through the various medical specialists, engineers, and even shipwrights.

The Roman people demonstrated an astonishing talent for organization and discipline, and this talent translated into a high level of training and leadership in Roman armies. While many ancient cultures produced skilled individual warriors, they rarely had a training program as evolved or detailed as that of the Romans. The Roman fascination with organization also enabled them to train on a grand scale, drilling large units in the complex maneuvers required to ensure victory over numerically superior opponents. The high percentage of leaders in a Roman army-leaders who fought on the front lines with the soldiers-ensured that the common legionary executed his part of the battle properly, and that he did so willingly, knowing he would be asked to do nothing which his superiors were not also prepared to do.