'At first the legionaries stood motionless, keeping to the defile as a natural protection: then, when the closer advance of the enemy had enabled them to exhaust their missiles with certitude of aim. they dashed forward...'
Tacitus' description of the defeat of Boudicca in Britain in AD 60 (Tacitus. Annals 14.37)
The great struggles with Carthage and the Hellenistic powers were fought and won by Rome’s militia army, but during the 2nd century BC this system of recruitment came under growing pressure. The acquisition of overseas provinces created a demand for large permanent garrisons and meant that many of the part-time legionaries were required to spend a decade or more in continuous military service. This interruption from normal life could easily spell ruin to one of the yeoman farmers who had traditionally made up the bulk of citizens eligible for military call-up. The Romans themselves began to worry that this class was in decline, and their fears for the future grew as a series of wars began with defeats and were only won after very hard struggles. Eventually the Republic was forced to abandon the militia system in favour of a professional army, recruited overwhelmingly from the poorest citizens. The change has sometimes been associated with the great commander Caius Marius, but may actually have happened far more gradually. Whether the change occurred as a result of long-term trends or sudden reform, it profoundly altered the character of the legions. Military service became a career which lasted for much of a man’s adult life, so that soldiers were increasingly separated from civilians. Legionaries ceased to be men of property, which meant that they had no source of livelihood once the army no longer required their services, and many proved willing to fight for their commanders against other Roman armies. Prolonged periods of civil war in the 1st century BC resulted in the collapse of the Republic, which was replaced by a form of monarchy known as the Principate.
Under the Principate the process of creating a professional army was completed. All troops now served in permanent units, many of which existed for many centuries. The rank and file were professional soldiers who spent 25 years with the colours, but in many of the more senior ranks aspects of the old militia system survived. Officers from the senatorial and equestrian classes commanded legions and auxiliary units respectively. Most senators in particular spent only part of their public career with the army, interweaving this with civil posts in the traditional manner.
Detail from a relief found in Rome and probably dating to the early 2nd century BC showing a parade of Praetorian guardsmen. The men wear ornate classically styled helmets, muscled cuirasses, and carry heavily decorated shields.
Marius and the capite censi
The creation of a professional army has often been attributed to Caius Marius. In 107 BC he was elected consul and sent to replace the commander in the Numidian war in spite of strong opposition from the Senate. Denied the right to raise new legions to strengthen the army in Africa, Marius was only permitted to take volunteers with him. In an unprecedented move, he appealed to the poorest citizens, men who lacked sufficient possessions to qualify for military service. These, the ‘head count’ (capite censi), responded with enthusiasm and proved themselves to be fine soldiers. The link between property and military service was broken for ever, recruits now needed only to be citizens and came increasingly from the poor.
(Above) A legion of 10 cohorts deployed for battle. Alt cohorts were equipped and trained to fight in the same way. which meant that they did not have to occupy a fixed position to be effective.
The change may not have been quite as sudden as this. Some scholars argue that Marius merely made open admission of a practice that was already common. Certainly the minimum qualification for service had been lowered, and there is a little evidence for poorer volunteers serving with the legions in many campaigns and effectively becoming career soldiers, although we do not know how many of these men there were. Even so, Marius’ reform was certainly an important stage in the transition from militia to professional army. Soon afterwards the last great rebellion of Rome’s Italian allies, an extremely brutal conflict known as the Social War, led to the granting of citizenship to virtually all of the communities south of the River Po. The alae disappeared, and now all troops were recruited into legions organized in the same way.
The new legions
Although many of the traditions of the militia legions were preserved, the new professional or semi-professional units were fundamentally different in their spirit and tactics. The new legions were much more permanent, keeping the same name and number throughout their existence. In the past each legion had carried five standards, an eagle, horse, bull, wolf and boar, but Marius gave each legion a single silver eagle as its standard. Legionaries who viewed the army as a career, not simply as an interruption to normal life, came to identify very strongly with their legion, and these units developed tremendous corporate spirit. Skilful leaders such as Caesar would play on soldiers’ pride in their legions and rivalry with other units in the army.
Soldiers no longer provided their own equipment, instead being issued with weapons, armour and clothing by the state. The differences between the various classes in the legion vanished, the cavalry and light infantry disappearing with them. All legionaries were now heavy infantrymen, armed alike with pilum and gladius. The men were still organized into centuries, though these were now all 80-men strong, and a pair of centuries composed a maniple. However, the maniple was replaced as the basic tactical unit by the larger cohort. This consisted of three maniples, one from each of the old lines, whose names were preserved in the titles of the centurions, and mustered 480 men as ‘paper strength’. Allied contingents had been organized into cohorts for some time, and Polybius twice mentions the formation in use with the legions in Spain during the Second Punic War. On one of these occasions he seems to say that a cohort consisted of three maniples, although the text is a little ambiguous. It may be that cohort was the term employed for any temporary unit larger than a maniple but smaller than a legion. It is also possible that conditions in Spain encouraged its use at certain times by the legions fighting there, but there is no good reason to believe that all legions at all times were organized into cohorts as well as maniples before Marius.
The cohort offered several advantages over the same number of men organized into maniples. In the first place it was a unit used to working together and must certainly have had its own commander, although none of our sources tell us this explicitly. He was most probably one of the six centurions commanding the centuries. One or several cohorts made up a coherent and effective detachment if a force was required for an operation not sufficiently large to warrant the use of an entire legion. In battle, the legion still most commonly deployed into the triplex acies formation, four cohorts in the front line and three in the middle and rear lines. However, each cohort was the same size and carried identical equipment. Such a legion could just as easily form in two or four lines if this suited the tactical situation. It was also far easier for a commander to control, since now he had only to convey his instructions to 10 cohort commanders instead of the leaders of 30 maniples. Cohorts were not forced to move only with the rest of the line, but could be shifted as individual units. The legion of 10 cohorts was far more flexible tactically and strategically than its predecessor the manipular legion.
A silver denarius minted in 49 вс showing a legionary eagle (aquila) flanked by two century standards (signa). Marius is credited with having given each legion a single eagle as its principal standard.
A reconstruction of the siege lines built by Julius Caesar's army at Alesia in 52 BC, giving a good impression of the high levels of engineering skill common in the professional legions At Alesia the Romans constructed two such lines - one facing inwards towards the defended town and the other facing outwards to guard against the Gallic relief army - each more than 17.5 km (11 miles) long, including 23 forts and with towers at intervals of c 24 m (80 ft) along the rampart.
Professionalism and the new permanence of the legions brought other advantages. Experience and technical knowledge was more easily preserved and passed on to the next generation instead of being lost each time the army was disbanded. During the 1st century вс the Roman army first began to display a mastery of engineering works unrivalled by any of its opponents. Legions contained specialists and skilled craftsmen as well as soldiers who willingly provided a labour force. Julius Caesar’s army included men capable of building a bridge across the Rhine, of constructing and repairing a fleet of ships, of building ramps and engines to storm Avaricum or lines of fortification to blockade Alesia into submission during his Gallic campaigns. These craftsmen were only formed into separate teams for the duration of a task, otherwise remaining dispersed throughout the cohorts and performing the same duties as the other soldiers.
The best legions produced by the militia system, hardened by long service and trained by experienced officers, had been very good indeed, perhaps as confident and tactically skilled as even the finest of the later professional legions. However, the new professional units were on average better trained and disciplined than their predecessors, simply because they were more permanent. The Romans believed that it took many years of successful fighting for a unit to reach the peak of its efficiency. One of Caesar’s officers contrasted a legion in its eighth campaign in Gaul and showing great promise, but still not quite as good as the veteran units of the army.
Under gifted and ambitious commanders the well-trained professional legions undertook the most intensive period of conquest in Rome’s history. Lacking integral light infantry or cavalry, Roman armies now relied on allies, often locally raised to provide these supporting arms, but it was always on the legions that the brunt of any operation fell. Men such as Marius, Sulla, Pompey, Lucullus and Caesar demonstrated the flexibility of the cohort legions time and again. In Europe, North Africa and the Near East the Romans took on very different, and often far more numerous, enemies and destroyed them, often with contemptuous ease. Overconfidence contributed much to the disaster at Carrhae in 53 вс, when Crassus’ army was virtually destroyed by the Parthians.
The legion of 10 cohorts still lacked a permanent commander. However, it became increasingly common for one of the governor’s deputies (legati) to be placed in charge. When fighting the German King Ariovistus in 58 вс, Caesar placed his quaestor and five legati in command of his six legions. The quaestor was an elected magistrate, a senator at an early stage in his career who was supposed to administer the finances of the province and act as the governor’s deputy. The legati were not elected but chosen by the governor from amongst his family, friends and political allies. Some of these might be former governors and army commanders, providing experienced, if still temporary, leadership at this level.
There were also still six tribunes in each legion. Some of these were still young, inexperienced aristocrats embarking on a political career, but an increasing proportion were from the equestrian order (the class was named after its original role as cavalrymen). Many of the latter were as professional as the men in the ranks, for it seems to have become common to serve over long periods of time. The frequency of foreign wars and the not-uncommon outbreak of civil conflict in the 1st century BC allowed many officers to see almost continual service.
Another important factor in preserving collected experience and skill in the army was the rise of the professional centurion. Although Polybius commented on the care taken to select determined fighters to fill the ranks of the centurionate, it is only in the Late Republic that these men become more prominent. In Caesar’s narrative of his own campaigns, it is the centurions more than any other grade of officer who receive attention and praise, both collectively and as named individuals. Men like Sextus Baculus in Gaul and Crastinus at the battle of Pharsalus in Greece (48 BC, where Caesar defeated Pompey) are depicted as heroic figures, who inspired the soldiers under their command. On several occasions Caesar notes that he promoted gallant centurions from lower grades in veteran legions to higher positions in recently raised units. Only once in the entire Caesarian Corpus is a man specifically mentioned as having risen to the centurionate from the ranks of the legions, and the individual in question was serving with Pompey not Caesar. Otherwise we have no real clue to the selection of these officers and whether they entered the army as officers or were promoted from the ranks. What is clear is that once a man joined the centurionate, he became an individual of some status and in time often wealth.
The post-Marian army was in many ways a more flexible and effective force than its predecessor. Its relationship with the Republic was also very different. To a great extent the old militia army had been the entire state and people under arms. Men were granted varying degrees of political influence in relation to the capacity with which they served in the army. Military service was sometimes glorious and sometimes profitable, but generations of citizens were willing to serve out of a sense of duty to the Republic with which they strongly identified. In essence the old hoplite ideal was preserved, since the men fighting for the state were the ones who had a greatest stake in it.
The professional soldiers came overwhelmingly from the poorest classes, whose direct political influence was negligible. The army fed and clothed such men, giving them an income and a sense of purpose. All of this was lost as soon as they were discharged. The Senate refused to acknowledge that the army was no longer a militia of the propertied classes, instead of a force of soldiers dependent on the army for a livelihood. The soldiers therefore now looked to their commanders to provide them with some means of support, usually a grant of farmland, when they returned to civilian life. A good general, one who had campaigned long and successfully with an army, especially one who was a gifted leader, was now able to create an army whose loyalty was to himself far more than the state which ignored the soldiers' problems. It is a striking feature of the Late Republic that the times of greatest conquest were intermeshed with recurrent civil wars. Legion turned against legion with much the same ruthless efficiency that they had shown fighting foreign opponents. The great conquerors were the major leaders in these internal conflicts, as time and again legions were marched on Rome to seize political power by force. The professional army was a major factor in making possible the upheavals which in time destroyed the Republican system of government and led to the creation of the Principate, a monarchy in all but name.
A memorial commemorating Marcus Caelius Rufus, a senior centurion of Legio ХIIХ, and two of his freedmen. Caelius was killed at the age of 53 when his legion and two others under the command of Publius Quinctilius Varus were ambushed and destroyed in Germany in ad 9. The inscription concludes by granting permission for his remains to be deposited here if they were ever found.