The Marian reforms were putative changes to the composition and operation of the Roman army during the late Roman Republic usually attributed to Gaius Marius (a general who was consul in 107, 104–100, and 86 BC). The most important of these concerned the altering of the socio-economic background of the soldiery. Other changes were supposed to have included the introduction of the cohort; the institution of a single form of heavy infantry with uniform equipment; the universal adoption of the eagle standard; and the abolition of the citizen cavalry. It was commonly believed that Marius changed the soldiers' socio-economic background by allowing citizens without property to join the Roman army, a process called "proletarianisation". This was thought to have created a semi-professional class of soldiers motivated by land grants; these soldiers in turn became clients of their generals, who then used them to overthrow the republic.
Belief in a comprehensive scheme of reforms under Marius emerged in 1840s German scholarship, which posited that any changes in the Roman army between the times of Polybius and Marius were attributable to a single reform event. This belief was spread relatively uncritically and was accepted as largely proven by the 1850s and through much of the 20th century. There is, however, little ancient evidence for any permanent or significant change to recruitment practice in Marius' time. The occurrence of such a comprehensive reform led by Marius is no longer widely accepted by specialists; 21st-century scholars have called the reforms a "construct of modern scholarship".
Other reforms to the army's operations and equipment, said to have been implemented by Marius, are also largely rejected by scholars. Few of them have any basis in the ancient and archaeological evidence. Others are wrongly dated or misattributed. Changes in the Roman army of the late republic did occur, but appear to have happened later than at the end of the 2nd century BC. Rather, these shifts were during the Social War and following civil wars, and emerged from circumstance rather than a reformist Marian vision.
Background
The Roman army traditionally found its manpower by conscription from the top five census classes. Those classes were assigned in decreasing order of wealth and allotted citizens to a corresponding century in the comitia centuriata. These citizens were called adsidui. Citizens who owned less wealth than that required for bottom of the fifth census class were called capite censi (lit. 'those counted by head') or proletarii. These least-wealthy citizens were grouped into a single century which voted after all the others. Under this scheme, the proletarii were exempt from conscription except when an emergency, called a tumultus, was declared; under such circumstances, the poorest were levied as well. The first documented instance of the proletarii being called up was some time in the fourth century; they first received arms at state expense in 281 BC, probably related to the start of the Pyrrhic War.
For much of the 20th century, historians held that the property qualification separating the five classes and the capite censi was reduced over the course of the second century to a nugatory level due to a shortage of manpower. The basis for that belief, however, was merely three undated Roman figures for the amount of property required to serve which would serve as evidence for reductions only if forced into a descending order. Many scholars have also now abandoned the notion that Italy suffered in the second century BC any deficit of manpower which would have driven such putative reductions.
Some or all of the following reforms have been attributed to Marius in modern historiography. They are, however, variably dated. Many modern sources date them to his first consulship, during the Jugurthine War against Jugurtha of Numidia, in 107 BC. However, it is also possible that other far-reaching actions, especially in opening army recruitment, were undertaken during Marius' repeated consulships from 104 to 100 BC during which Rome faced the serious threat of Germanic invasion.
Ancient attributions
Marius was credited with setting the precedent for recruiting the poor by the historian Valerius Maximus writing in the early 1st century AD. Two further reforms (distinguished from mere actions taken by Marius) are attributed, in sources postdating his career by hundreds of years, to Marius directly: a redesign of the pilum and sole use of the eagle as the legionary standard.
Army proletarianisation
The main putative reform attributed to Marius is a change to recruitment starting, as is generally held, in 107 BC. In that year, Marius was consul, had himself assigned by plebiscite to the war against Jugurtha, and recruited additional soldiers to send to war by enlisting volunteers from both those in the five census classes and also the capite censi. The senate had in fact given Marius the right to conscript, but he chose to also enrol some three to five thousand volunteers.
Various motives have been ascribed to Marius' decision to accept volunteers. The motive attributed in Sallust, Marius' personal ambition to seize power, may more reflect Sallust's desire to connect the republic's collapse with moral decline and failure to adhere to tradition. The second edition Cambridge Ancient History viewed it as an expedient to evade popular opposition to conscription. R J Evans, with whom François Cadiou agreed, instead proposed that Marius' decision emerged from his promise of a quick victory in Numidia followed by an energetic effort to follow through by raising and bringing an army as quickly as possible to Africa so to maximise his time campaigning as consul. Regardless, after Marius' victorious return from the Jugurthine War, his volunteers were discharged and, in the following Cimbric War, he assumed command of consular legions recruited via hitherto normal procedure.
It was believed that Marius' decision to enlist volunteers from the capite censi changed the socio-economic background of the army by allowing the poor to take it over. These poor soldiers then professionalised and lived only as soldiers. These professional soldiers, disconnected from a society in which they had no property stake, over time became clients of their generals who then used them to seize power in Rome and plunge the republic into civil wars that eventually brought about its collapse. It is largely accepted, however, that Roman conscription continued to take place after 107. Nor is there much evidence that later Roman armies during the 1st century BC were made up of volunteers; almost all ancient references to army recruitment, outside private armies, involve conscription.
Conscription continued after Marius' time, especially during the Social War, and the wealth and social background of the men who joined before and after the opening of recruitment changed little. Pay remained extremely low – only five asses per day – and irregular. Moreover, although the surviving sources frequently characterise soldiers as "poor", these sources largely reflect the perspectives of the elite, by whom the vast majority of the population were considered "poor" and for whom the notion of poverty was broader than actual landlessness. Many of the soldiers of the 1st century BC possessed modest lands. Nor did the legions meaningfully professionalise: as, in general, both soldiers and commanders served only for short periods intending, respectively, to secure plunder or political advancement from military victory. There is little evidence that this putative change in army recruitment created anti-republican client armies.
Equipment changes
Beyond changes to army recruitment, there are two other reforms attributed to Marius specifically in the ancient sources: a redesign for a javelin, and the designation of the aquila (eagle) as the universal legionary standard.
Plutarch relates that Marius altered the design of the Roman pilum, a heavy javelin designed to stick into shields, by including a wooden peg which broke when the javelin was thrown. Many scholars believe this was to prevent the javelin from being thrown back, but it is more likely that the swinging motion of the broken peg was meant to force someone to discard a shield into which the javelin was struck. Regardless of the efficacy or purpose of the redesign, archaeological evidence from the 80s BC through to the early imperial era show that Marius' redesign was not adopted. Roman pila without Marius' peg often bent or broke on impact, but this was more likely a by-product of their long, narrow shanks than an intentional feature.
Pliny's Natural History attributes Marius with adopting the eagle as the universal legionary standard. This has been interpreted as a rallying symbol for each cohort. Pliny's claim, however, is incorrect; sources show late republican and early imperial legions with other animal symbols such as bulls and wolves.
Modern attributions
Most of the reforms attributed to Marius in various sources emerged only in modern times. These reforms have little ancient pedigree. They rest largely on the basis of comparison between the army described by Polybius and the army in the texts of the 1st century BC with an assumed attribution to Marius.
Equipment at state expense
It is also sometimes claimed that Marius – because the poor citizens enrolled could not afford to purchase their own weapons and armour – arranged for the state to supply them with arms, displacing the traditional system of self-purchase. Such a scheme may have been incipient during Gaius Gracchus' plebeian tribunate (c. 122 BC); according to Plutarch, Gracchus passed a law to abolish deductions from soldier pay for clothing. The Italian historian Emilio Gabba argued, for example, that Plutarch's text could be emended from merely encompassing clothing to equipment more generally, reflecting Gabba's belief that this policy emerged from the recruitment of poor soldiers unable to pay for their own equipment.
Neither a Gracchan abolition of deductions for equipment or a Marian programme to equip soldiers is attested in the evidence. There are no indications that Gracchus' law ever came into effect and literary evidence indicates that deductions for clothing and equipment were common in the imperial army of Augustus into the 1st century AD. If Marius purchased equipment for his troops in Numidia at his own expense, later generals and the state in general did not do so.
"Marius' mules" and training
Marius is said in ancient sources to have moved much of the baggage off beasts of burden and onto the backs of the common soldiers, giving them the moniker muli Mariani ("Marius' mules"). Some modern historians have read this action as a permanent reduction in the size of Roman baggage trains, increasing the speed of army movement. However, attempts to force soldiers to carry their own equipment were common among successful generals at the time; Marius' predecessor in Numidia, Quintus Caecilius Metellus, as well as Scipio Aemilianus, was said to have forced their soldiers to carry their own equipment.
Some modern historians have also attributed to Marius reforms in the training of Roman soldiers which ostensibly reflected a professionalising service. Such training and drilling, however, had become common before Marius due to the loss of collective experience in the generations after the Second Punic War. Quintus Fabius Maximus Aemilianus drilled his men for almost a year before deploying them in the Lusitanian War (c. 145 BC); Scipio Aemilianus, for example, drilled his men before his campaigns against Numantia (c. 133 BC); Metellus similarly drilled his men prior to their departure to Africa in 109 BC. Such attempts to reintroduce discipline reflected the recruits' lack of military training rather than a class of budding professional soldiers.
Unit composition
Modern historians have sometimes credited to Marius the abolition of Roman cavalry and light infantry and their replacement with auxilia. There is no direct evidence for this contention, which is driven largely by literary sources' silence on those branches after the 2nd century; continued inscriptional evidence attests both citizen cavalry and light infantry into the end of the republic. The decline of Roman light infantry has been connected not to reform but cost. Because the logistical cost of supporting light infantry and heavy infantry was relatively similar, the Romans chose to deploy heavy infantry in extended and distant campaigns due to their greater combat effectiveness, especially when local levies could substitute for light infantry brought from Rome and Italy.
Marius has also been credited with the introduction of the cohort (a unit of 480 men) in place of the maniple (a unit of only 160 men) as the basic unit of manoeuvre. This attribution is rather dubious and there is no ancient evidence of it; cohorts may have been used as far back as the Second Punic War near the end of the third century BC. The cohort itself emerged as an administrative unit conscripted from Rome's Italian allies and is first attested in a description by Polybius, a usually reliable historian, of a battle which occurred in 206 BC. By the 130s BC, through the Spanish wars and operations with Italian allies, the cohort had developed into a tactical unit. While, after 109 BC, the maniple disappears from the literary evidence, Marius' predecessor in Numidia is documented to have used cohorts in battle: if cohorts replaced maniples around this time, Marius was likely not responsible.