The Legion. The core of the Roman army of the Republic and most of the Empire was made up of formations of heavily armed and armored infantry. The largest standing unit was the legion, theoretically composed of about five thousand men. (The legion and all of its subdivisions were ordinarily smaller in practice than on paper.) This legion was divided into ten numbered “cohorts,” the first being about twice the size of the others. Each cohort in turn consisted of six “centuries” made up of about eighty men. Finally, centuries were divided into contubernia of eight men. The century was commanded by a centurion; he was often an experienced soldier promoted from the ranks, but sometimes a political appointee instead. He was assisted by a standard-bearer and two other officers. The cohorts did not have officers of their own but appear to have been in the charge of their senior centurion. The legion was commanded by two or more military tribunes (no relation to the magistrate of similar name). In practice, however, the tribunes often served as staff officers for the magistrate or promagistrate in command of a whole army rather than directing a particular part of the army. Tribunes were often, in fact, young aristocrats who needed military experience more than the army needed them. Also attached to the commander could be a number of legati. These were also aristocrats, but normally of more experience, and they might be dispatched with a force of their own if the army needed to be in more than one place at a time. Also attached to the legion as a whole were a small group of cavalry, some artillery, and an “eagle-bearer” carrying the legion’s standard.
Equipment. These soldiers were equipped in uniform fashion. They wore armor from shoulders to waist made of scale, mail, or bands (and the famous protective leather skirt below this). There was also a large helmet, a heavy, partly cylindrical shield with a central boss, and greaves. The main weapons were fairly heavy throwing spears and short, broad swords. The former were cast at modest range to injure but also to disorganize the enemy; the latter were primarily thrusting weapons. Some may also have carried some kind of knife, and the heavy shield could be used effectively to strike an enemy. Cavalry were equipped more lightly than infantry and often carried a stabbing spear or lance. Legionary cavalry were often more important for communications and scouting than for battle.
Auxiliary Forces. Around the legions, and sometimes even outnumbering them, were “auxiliary” troops provided by Rome’s allies. Sometimes this situation was a matter of mutual interest, but more often it was a condition of peace with Rome. Republican auxiliary troops were equipped in national fashion. For Italians, this gear was essentially Roman. For Gauls and Africans it could vary considerably. Under the Empire, auxiliary infantry was generally organized like the Roman forces, but the largest unit was the cohort, not the legion. This unit was commanded by a Roman prefect. Most of these units also used arms and tactics like those of the legions. However, others provided the Roman army with its light-armed troops and missile-firers (archers, slingers). Nearly all of the “Roman” cavalry were actually auxiliary. The main unit was the ala (wing) of about five hundred men, commanded by a Roman prefect or indigenous leader. This unit was divided into sixteen turmae (squadron, singular turma), each lead by a decurion. Some auxiliary cohorts of the imperial army also combined a full compliment of infantry with a substantial number of cavalry.
Recruitment and Service. All able-bodied male Roman citizens between seventeen and forty-six (older in emergencies) were liable for service in the Republican army. At the beginning of a campaign the consul (or other responsible official) would hold a levy to which the potential soldiers were summoned. From these he chose enough men to fill the number of legions to be filled. Originally levies were held at Rome, but as Roman citizenship spread, regional levies were also added in times of need. A man was liable for sixteen years of service, but would not normally have to serve more than six years consecutively. For most of the Republic there was a minimum property qualification to serve in the army, though its value declined over time. (The theory was apparently that the best soldiers were those with something to fight for.) The general Marius seems to have been the first to recruit among the landless as a matter of course, at the end of the second century b.c.e. It soon became common practice.
Professionalization. Poorer soldiers had less economic motivation to return to civilian life. Rome’s wars grew increasingly distant over time and so there was greater need to keep the troops away. Thus, it was probably not surprising when Augustus shifted the army to a more professional basis. The term now, apparently, became sixteen years plus four more of special veteran service. Troops stayed in the army for the full term even when not campaigning and received a substantial cash bonus on discharge. Units of the army also developed continuing histories; some can be traced for two centuries. The levy was never actually abolished, but the career was attractive enough that volunteers were normally sufficient. Auxiliary service also came to be more professionalized. There was a standard term of service (twenty-five years) and a conventional grant of Roman citizenship at its end.
Engineering. The Roman army had no separate corps of engineers, but most of the soldiers were taught construction skills of various sorts. The most basic was construction of the field camp set up at the end of each day’s march during war. This bivouac was not a heavy fortification, but it prevented easy infiltration or sneak attack by an enemy. It must also have been valuable as a symbol of Roman discipline and occupation. When occasion demanded they could also construct much more elaborate defenses as well. Soldiers also needed to be able to build and use various devices of siege warfare: ramps, mobile towers and shelters, rams, and tunnels. Special needs might also require unusual items: Julius Caesar’s bridge across the Rhine, field fortifications to guard the army’s flanks, fences to protect a naval beachhead. Additionally, legionary soldiers operated artillery—both large, cross-bow-like bolt-throwers and even larger, catapult-type stone-throwers. Either would have been used primarily in sieges or against packed groups of men.
Military Law. Roman soldiers were citizens and thus subject to ordinary law except when some specific exception was made. This exception happened primarily in two areas: criminal and family law. A soldier accused of a criminal offense, including theft and violations of military discipline, was subject to the commander’s summary judgment rather than a trial. The soldier also lacked the citizen’s normal immunity to corporal punishment. Minor offenses could be punished correspondingly—loss of pay, reduced rations, or the like. More serious infractions, however, were met with beatings or death. Violations of military discipline were often punished at the unit level as well as the individual level. Most famously, a unit might be “decimated.” That is, one tenth of the soldiers were to be clubbed to death by their fellows. Under the Empire, steps were taken to weaken the legal ties of soldiers to their families. For the first two centuries c.e., soldiers could not form legal marriages, though the rule seems to have been widely ignored. Soldiers with living fathers were given the exceptional ability to hold and bequeath property independent of those fathers.
Toward the end of his conquest of Gaul (52 b.c.e.), Julius Caesar cornered the leader of a major uprising in the hilltop town of Alesia. His troops built a ring of fortifications to contain the Gauls in the city, then built another around themselves to fend off the huge relief force that arrived soon. He describes the works himself in his memoir of the Gallic campaign.
Both construction material and food supplies had to be gathered and great fortifications be built at the same time, despite our reduced forces, which were going further and further from camp. Occasionally, the Gauls tested our defenses and attempted sallies in full force from the town from several gates at a time. As a result, Caesar thought these works needed to be reinforced so they could be defended by a smaller force. Tree trunks and strong branches were cut off and their ends were smoothed and sharpened and continuous trenches of five-foot depth were dug. The stakes were set into the trenches, fastened at the bottom so they could not be removed, and the other end was allowed to stick up. Five ranks of these were joined and bound together so that anyone who entered would impale himself on very sharp points. This they call “boundary markers.” In front of these, arranged like the dots on a “five” on a die, three-foot deep pits were dug, narrowing at the bottom. Into these were set smoothed sticks, thick as a man’s thigh, sharpened and fire-hardened at the end, and projecting only a few inches from the ground. To firm and stabilize them, the ground was trampled down for a foot from the bottom of the pit; the rest of the pits were covered in twigs and branches to hide the trap. There were eight rows of these, three feet apart from each other. These were called “lilies” from their resemblance to the flower. In front of these lilies, foot-long sticks with iron hooks attached were completely buried in the earth and scattered everywhere at modest intervals. They call these “spurs.”
The Early and Late Armies. The Roman army remained remarkably stable over its history, but there are a few significant differences at the beginning and end of the period. The armies that fought the Punic Wars were based on the “maniple” of two centuries, not the cohort of six. This maniple was a slightly more mobile unit, but too small to operate on its own as well as the cohort did. There was also a little variation in equipment within the legion. There were skirmishers up front, and the back rank had thrusting (not throwing) spears. The army of the late
Empire changed rather more. Emperors created more and more legions and auxiliary units, but these were much smaller than before. A legion might have as few as one thousand men. Cavalry became more prominent (though infantry was always more numerous). Finally, from time to time “barbarian” forces were absorbed into the army for political reasons. Unlike Republican auxiliaries, these were large groups and not well integrated into the Roman command structure.
The Army in Battle. The structure offerees was actually more flexible than the century/cohort/legion scheme might suggest. Field commanders made free use of “vexillations” (vexillum, or “military standard”)—temporary, ad hoc units. These might be single cohorts, segments of one or more legions, combinations of legionary and auxiliary troops, or even groups of picked individuals. The importance of such vexillations even grew under the late Empire. Whether permanent or temporary, units had considerable freedom of action in battle. This freedom was not so much a matter of deliberate choice as poor communications and surveillance. A general essentially had to choose between a position in the rear from which he could see the whole battle (but give orders only inefficiently) or one closer in where he could direct the surrounding troops (but not tell what else was going on).
Infantry and Cavalry. Most Roman battles were contested primarily by masses of infantry that collided and fought. If a clash was not decisive, they would pull back briefly, then try again. Eventually, one side would usually start to flee long before most were actually killed. If a hole opened up in the center or end of an enemy’s line, it was much easier to roll up the rest by attacking from two directions at once. Cavalry could be used to charge enemy infantry, but only if they did not hold their ground well. Otherwise, it could attack stragglers or those in flight and protect the flanks of an infantry formation. The military effectiveness of fire and (except in special circumstances) archery was much less than it is portrayed to be in modern television and movies.
The Army and Society. Except perhaps for the church of the later Empire (which had as yet no central authority), the Roman army was the largest organization in the ancient world. Naturally it had effects on the larger society of which it was a part. First, Rome was at war, often on multiple fronts and far from Italy, for almost the whole of the Republic. The militia-style organization of the army and
the extensive needs of this massive warfare combined to put massive demands on the ordinary citizenry. A large percentage of men of military age were in service every year, often for years at a time. This service created massive social and economic disruption at home, even for families whose members survived. Second, the legions contributed to the “Romanization” of the Empire. When legions fought or were stationed far from Italy, they brought with them the Latin language and other aspects of Roman culture. Under the Empire they often settled in the same areas after retirement. Moreover, the auxiliary forces were a good career path for those who wanted (or could tolerate) a Romanized lifestyle. None of these things forced anyone to become more Roman, but they certainly encouraged it. Third, the army encouraged a more sophisticated economy (though the extent of this effect is debated). The soldiers were paid in coins and so had cash to spend. Taxes to pay them were collected in coin, so taxpayers had to have at least some cash as well. Before the coming of Rome, much of the eventual empire was dependent on barter and traditional entitlements to move goods, a much less efficient system than one that uses money. Under Roman rule even small farmers had to be part of the money economy. While the army’s purpose was certainly not to lead Rome to a monetary economy, that must have been one of its effects in at least some degree.
Frank E. Adcock, The Roman Art of War under the Republic (New York: Barnes & Noble, 1960).
J. B. Campbell, The Roman Army 31 B.C.-A.D. 337 (London & New York: Routledge, 1994).
Arther Ferrill, The Fall of the Roman Empire: The Military Explanation (London: Thames & Hudson, 1986).
Adrian K. Goldsworthy, The Roman Army at War 100 B.C.-A.D. 200 (Oxford & New York: Clarendon Press, 1996).
Michael Grant, The Army of the Caesars (New York: Scribners, 1974).
L. J. F. Keppie, The Making of the Roman Army: From Republic to Empire (London: B.T. Batsford, 1984).