Roman Legions: Formations

The Roman Legion, renowned for its discipline, organization, and innovation, stands as one of the most formidable military forces in ancient history. The success of Rome, from a small city-state to a vast empire dominating the Mediterranean world, can be significantly attributed to the strategic prowess and tactical acumen of its legions. This page delves into the various tactics employed by the Roman Legion, tactics that have been studied and admired for centuries for their effectiveness in various combat situations.

Formations of the Late Republican Army

Often the Late Republican Army would have the legions holding the centre line with the auxiliary infantry on either side, and the auxiliary cavalry on the wings. Tacitus describes this formation being adopted by Furius Camillus, proconsul of Africa.

The legion was in the army’s centre; the light cohorts and two cavalry squadrons on its wings. 

Tacitus, The Annals of Imperial Rome: Book II: Chapter 52 – War in North Africa.

Formations of the Legion

Forming the Century

The configuration for the century most frequently given is an arrangement of 10 files and 8 ranks with the files on 0.9m (3’) intervals and the ranks on either 0.9m (3’) or 1. (4’) intervals. Each rank may have been offset to cover the gaps between men and to provide more room for manoeuvre.

The figure shows that configuration for a maniple of two centuries arranged front to back. Some authors say this was a muster or manoeuvre formation and that in battle the two centuries would have been side by side, as they are depicted a little further on.

Two centuries of eighty legionaries made a maniple, with three maniple’s to a cohort. The centuries placed one behind the other. The most likely configuration is 16 files by 10 ranks. It has the advantage of scaling down by units of 5 or ten as the maniple strength was depleted. Since the number of men in a cohort could vary considerably the formation must have been scalable in some consistent manner so that its fighting efficiency was not destroyed by the reduction in manpower.

The typical formation, described above, uses a spacing of 0.91m (3′) for the files and 1.22m (4′) for the ranks; allowing for the centurion, then, the cohort would have a front of 15.85m (52′). If the three cohorts fought side by side, as is always depicted, then their combined front would have extended to 48.16m (158′). The cohort would, in essence, be a miniature phalanx, 10 ranks.

Intervals between cohorts

Intervals between cohorts were necessary to maintain the cohesion of the units forming battle lines and to prevent them dissolving into a disorganized mass. It was easier for battle lines to advance and maintain formation if this was carried out at a cohort level, rather than by a huge and unwieldy continuous line. By the time of Caesar it is clear that the cohort had become the fundamental tactical unit. He describes battle formations and troop movements in terms of cohorts and legions appear more as administrative units than battlefield tactical units. Caesar sends cohorts and groups of cohorts, not legions, on flanking manoeuvres.

Intervals allowed light troops to make sallies against the enemy and then retreat to safety.

Antonius gave him the [light-armed] troops, and when the enemy made his attack, he fell upon them, not as on former occasions, at the same time withdrawing towards the heavy-armed soldiers and retreating

Plutarch – Plutarch’s Lives, Life Of Antonius: XLI

Intervals between cohorts in battle order are, thought to have been equal to the cohort front ; but though this was true of the era of the Punic wars, there is much room to doubt such intervals in Caesar’s time. No doubt there was an interval, in close (three-foot) order there were intervals between cohorts equal to cohort front; and in open or battle (six-foot) order, these intervals were quite filled up. As the third line was apt to be held in reserve and in close order, a legion in battle order would have the first two lines deployed, — without intervals between cohorts and the third line deployed into close order with intervals equal to cohort front.

Position of Cohorts within the Battle line

The discussion concerning the placement of cohorts in the battle line come from the writings of Vegetius, in which he describes the Double Acies formation or 5-5.

Position of the First Cohort

The first cohort, which was a double cohort, is placed on the right. This would have been the weakest point in the line as a legionaries shield is on his left, leaving his right side more exposed.

The legion should consist of ten cohorts, the first of which exceeds the others both in number and quality of its soldiers, who are selected to serve in it as men of some family and education. This cohort has the care of the eagle, the chief ensign in the Roman armies and the standard of the whole legion, as well as of the images of the emperors which are always considered as sacred. It consists of eleven hundred and five foot and one hundred and thirty-two horse cuirassiers, and is distinguished by the name of the Millarian Cohort. It is the head of the legion and is always first formed on the right of the first line when the legion draws up in order of battle.

Vegetius: De Re Militari Book 2: Chapter 6, Para 1

Position of the Third Cohort

The Third Cohort is the positioned in the centre of the line, while possibly not as important as the flanks it would need to be full of seasoned troops, to give courage to the less experienced cohorts, second and forth to its flanks.

The third is composed of five hundred and fifty-five foot and sixty-six horses, generally chosen men, on account of its situation in the centre of the first line.

Vegetius: De Re Militari Book 2: Chapter 6, Para 2

Position of the Fifth Cohort

The fifth Cohort is placed on the left flank, which again is described as important and so has seasoned troops in it.

The fifth has likewise five hundred and fifty-five foot and sixty-six horse, which should be some of the best men, being posted on the left flank as the first cohort is on the right. 

Vegetius: De Re Militari Book 2: Chapter 6, Para 2

Position of the Sixth Cohort

The fifth Cohort is placed on the left flank, which again is described as important and so has seasoned troops in it.

The sixth includes five hundred and fifty-five foot and sixty-six horse, which should be the flower of the young soldiers as it draws up in the rear of the eagle and the images of the emperors, and on the right of the second line. 

Vegetius: De Re Militari Book 2: Chapter 6, Para 3

Position of the Tenth Cohort

The Tenth Cohort is placed on the right flank, behind the fifth, again Vegetius describes it as important and so has seasoned troops in it.

The tenth consists of the same number of five hundred and fifty-five foot and sixty-six horses and requires good men, as it closes the left flank of the second line.

Vegetius: De Re Militari Book 2: Chapter 6, Para 3

The Other Cohorts

by implication the weakest cohorts thus appear to be the ninth and seventh and the fourth and second, and it would be in the first of these two pairs that one might expect to find recruits in training.

The Simplex Acies

The Simplex Acies was rarely used, and only for a specific tactical reason such as to extend the line to overlap enemy flanks or meet wider enemy formations and protect its own flanks. This happened in to Caesar at the Battle of Ruspina in 46 BC, as detailed below.

Caesar drew up his army in a single line, being obliged to do so by the smallness of his numbers; covering his front with his archers, and placing his cavalry on the right and left wings

The African War: Julius Caesar Book I: Chapter 83

The Duplex Acies

The duplex acies consist of two lines each with 5 cohorts in one line and the remaining 5 cohorts in the second. The duplex acies gives fewer reinforcements and reserves but a longer line to prevent outflanking manoeuvres. The duplex and triplex acies were the most commonly formations used by Caesar.

The Duplex Acies

Caesar, hoping to surprise this legion, and anxious to repair the loss sustained that day, left two cohorts employed in the works to make an appearance of intrenching himself, and by a different route, as privately as he could, with his other cohorts amounting to thirty-three, among which was the ninth legion, which had lost so many centurions, and whose privates were greatly reduced in number, he marched in two lines against Pompey’s legion and his lesser camp.

The Civil War: Julius Caesar Book 3: Chapter 67

The Triplex Acies

The triplex acies were lines consisting of 4 cohorts in the first, 3 cohorts in the second, and 3 cohorts in the third. This 4-3-3 arrangement of cohorts has been taken to be the standard for a legion in triplex acies formation. It obviously developed from the triple-line formation of the manipular legion.

The three lines were some 150 feet- 200 feet apart, although that’s still debated by historians.

Caesar refers to this formation in his Gallic Wars.

Caesar had three lines, four cohorts out of each of the five legions formed the first line. Three more from each legion followed them, as reserves: and three others were behind these. The slingers and archers were stationed in the center of the line; the cavalry closed the flanks.

The Civil War: Julius Caesar Book I: Chapter 83

The middle line of three cohorts would act as the reserves mentioned by Vegetius and Onasander whilst the rear line could carry out outflanking manoeuvres and if necessary turn around to face an enemy
attacking from the rear.

Quadruplex Acies

Caesar states that Scipio’s normal line of battle was the quadruplex acies, but his first line was made up of cavalry interspersed with elephants (B. Afr. 41), probably with a triplex acies of legionaries behind this.

Scipio, when the latter, fearing lest he should lose the town, whence he procured water and other conveniences for his army, resolved therefore to preserve it, at all hazards, and brought forth his whole army, and drew them up in four lines, forming the first of cavalry, supported by elephants with castles on their backs.

Julius Caesar, The African War: Book I: Chapter 41

To oppose and outflank these elephants at Uzitta, Caesar sent reinforcements to each wing to create a fourth line of cohorts.

When Caesar came to the place, he found Scipio’s army in order of battle before the intrenchments, the elephants posted on the right and left wings, and part of the soldiers busily employed in fortifying the camp. Upon sight of this disposition, he drew up his army in three lines, placed the tenth and second legions on the right wing, the eighth and ninth on the left, five legions in the centre, covered his flanks with five cohorts, posted opposite the elephants, disposed the archers and slingers in the two wings, and intermingled the light-armed troops with his cavalry.

Julius Caesar, The African War: Book I: Chapter 81

A Legion Forming a Square agmen quadratum (the hollow square)

A legion in three lines could readily form square by leaving the first, second and third cohorts facing to the front; by facing the fifth and sixth to the right; the fourth and seventh to the left, and by facing the eighth, ninth and tenth to the rear. The term orbis may have come from the natural habit of flattening out the corners of such a square for easier defence. It is difficult to imagine the manoeuvre by which a legion deployed into anything approaching an actual circle and again deployed into line. It may have been an irregular half-square, half -circle, according to the accentuation of the ground or to the conditions demanding a defensive formation.

  • the testudo (turtle) was used when advancing or retreating under heavy fire. The front ranks held their scuti in front of them while the internal ranks held theirs over their heads.

On the march, cohorts could be organized into:

  • the agmen quadratum (the hollow square): four columns of troops mraching in parallel. Used when in hostile territory since it was easy to shift into a triplex acies at the first sign of trouble.
  • the orbis (the circle) was used if the legion had to retreat under fire

On rare occasions there was a quadruple line. The fourth was intended to protect a flank and might consist of some cohorts specially detailed and marshalled at an angle to the general line. Such was Caesar’s disposition at Pharsalus. The auxiliary troops were drilled to conform to the same methods. They had not the cohort formation, but they were utilized so as to sustain the legionary tactics, much as the velites of old had been. The bowmen and slingers were mere skirmishers having no definite tactical position.

An army of seven legions in three lines — twenty -five thousand men field strength — would take up somewhat less than a mile and a half of front. The defensive formation of the legion was in one line (acies simplex) or in a square (acies quadrata) or a circle (orbis). The one line was usual for the defence of breast-
works or of the camp, — depth being unnecessary, as reserves were kept for the protection of the gates and for sorties. The five front ranks were on the rampart without intervals, the five rear ones at the foot of the rampart. Sometimes only two ranks were on the rampart and the three other ranks of the ordo back of it in reserve, while the rear ordo of five ranks was similarly disposed at the left of the front ordo. The space allowed for the usual defensive line was six feet per man; or with only ordo depth and assuming that the centurions were not in line, two hundred and sixteen feet for the maniple, four hundred and thirty- two feet for the cohort, and forty-three hundred and twenty feet, four fifths of a mile, for the legion. A single line disposition was sometimes practiced to resist attacks in the field, but the cohort retained its front of about one hundred and twenty feet, and the intervals being closed, the legion had but twelve hundred feet front. How much of a circle the orbis was, we do not know. It was formed for defence in the field against overwhelming and surrounding forces. To resist such an attack, the cohorts drew up in what was the equivalent of our hollow square. Smaller bodies might form circular groups, using their shields and hurling their spears and occasionally falling to with the sword. Were not the hollow square also described we should be tempted to believe that the orbis was the same formation.

The Baggage Train

The baggage consisted of pack-train (impedimenta) and the soldier’s own load (sarcince), which Cicero says was sixty pounds in addition to his armour and weapons, — a possible maximum. Sutlers (mercatores) were the only persons accompanying the army who used carts. The tents were of skins, ten feet square. Each tent could accommodate eight men, of whom two would probably be on duty. Each centurion had a tent; the camp-followers must be sheltered ; the higher officers had servants and more tents than the lesser. With tools for intrenching, tent-poles and pegs and the usual baggage carried, there could be five hundred and twenty sumpter-mules for a field legion of thirty-six hundred men, —or one animal for every seven men. This was all there was to the pack-train, and is not far astray, Marius invented a forked stick or pole (muli Mariani) for convenience in carrying the sarcince. The bundles of rations, clothing, etc, were tied to this, and it was the ration for fifteen days, grain imgronnd, weighed probably twenty-five pounds. The rest of the kit, armor, etc., much more than doubled this load. Cicero’s estimate may be considered high.

The allied legions of old times had all disappeared. A legion no longer meant one Roman and one allied legion, or ten thousand men. It meant simply a body of ten cohorts. In place of the allied legions there was a larger force than theretofore of light troops armed like legionaries, but less heavily, and considerably more bowmen and slingers. The light troops had a leather jerkin but no armour, and carried the round shield (parma) instead of the cylindrical scutum. The bowmen and slingers wore no armour at all.

Roman Cavalry Tactical Units

In the cavalry, turma of thirty-two enlisted men was the tactical unit. It rode in four ranks of eight front. It
has been thought that the ranks were open so that the men stood checker-wise. There were three decurions to each turma, the senior being its chief. The turma must have been a body about forty feet square, reckoning crudely five feet front and ten feet depth per mounted man. Twelve turmae were an ala (wing) or regiment, which may have been formed in two (or three) lines, each say four hundred and forty (or two hundred and eighty) feet long, counting intervals equal to turma-front between turmae, which were more essential in the cavalry than the infantry. The cavalry was commanded by praefectus equiturn. In larger bodies, in which the cavalry often acted, we must guess at the formation. It no doubt, at this era, conformed much to the habits of the peoples furnishing the troops, modified by Roman experience and the necessities of the army. Ceasar had no Roman cavalry, properly speaking. It was all recruited among the Gauls or Germans.

The Order of the March

The order of march (agmen) was quickly formed by facing the legion to the right or left, according as it was to move. The cohorts thus followed each other in order. If to the right, the maniples of each cohort would be pilani, principes, hastati; if to the left, the reverse. The depth of the file, on facing to the right or left, would be column front, i.e. eight or ten men ; and as the men could comfortably march in a breadth of three feet each, this front could be reduced to twenty-four or thirty feet by simply dressing on the front rank man ; or by making each second ordo fall in behind its first, this could be again reduced to fifteen or twelve feet front.

It was a ‘‘column of fives or fours.” This was called marching in column of maniples The legion in column of maniples could then file in any direction. Or the legion could march in column of centuries (centuriatim or ordinatim) by the maniple on the right or left marching straight forward, followed in order by each succeeding maniple. In this order each cohort would march with its centuries in regular sequence: first ordo of pilani, second ditto; first ordo of principes, second ditto ; first ordo of hastati, second ditto. In other words, the centuries (ordines) would successively follow each other. This column would hare a front of twelve men if the cohort had only field strength ; but we can imagine it deployed into a “column of sixes.” In its full width it was employed only in open country. Few roads would accommodate so wide a column.

Line was again (quickly formed from column by converse means, just as it is to-day. Deployments were sometimes made by the left instead of the right, as, e. when circumstances would expose the right flank, which, with the shield on the left it will be remembered, was considered the weak or open side (latus apertum). Thus, in debouching from a defile, to deploy at its mouth, the column might issue left in front, and deploy to the right of the leading century or cohort. The open side would not be thus exposed.
The men could readily march each in a space of four feet from front to rear. A cohort of field strength (three hundred and sixty men) would thus take up, in length of column, if marching centunatim full front, one hundred and twenty feet; half front, two hundred and forty feet. If manipulatim and the men kept their distance of three feet, as they could for short distances, it would be one hundred and eight feet long; if the column was extended so as to allow each man four feet, it would be one hundred and fifty- two feet long in full front, three hundred and four feet in half front. It scarcely seems probable that the column could be allowed to drag its length out so much beyond the space required by the line of battle. But marches then were governed by the condition of the roads as they are to-day, and it was, no doubt, difficult to keep the column closed up.

The legion could march in line (acies instructa); in column (agmen pilatum) in square (agmen quadratum).

The march in line was only employed on the battlefield and had the same advantages and disadvantages, saving the absence of artillery, as it has today. If the legion in three lines wished to take ground to the right, and still remain in line of battle, it could do so by facing the whole body to the right and marching the three columns so made as far as desired. By a halt and front the line of battle was again formed in three lines. This enabled a legion to change its position obliquely without great difficulty.

If the line was on difficult ground it could advance by column of wings (cornu). he right wing would have cohorts 1, 5, 8 ; the centre would have cohorts 2, 6, 9; the left wing would have cohorts 4, 3, 7, 10.

Each of these would march by the flank and file to the front, like our forward by the right of companies. On halting, each cohort would file to its proper place in line and dress forward on its right.
In marching in column the cohorts followed each other according to number (No. 1 to No. 10 from right to left). Thus marching centuriatim gave the legion, with an interval of twenty feet between cohorts, some fourteen hundred feet of length; if doubled up, twenty-six hundred feet.

Baggage-train of a Legion

The baggage-train of a legion is estimated at five hundred and twenty pack-animals. In a breadth of forty feet eight animals could go abreast, which gave sixty-five ranks of them; or allowing ten feet for each, six hundred and fifty feet for the pack-train, or thirteen hundred feet if doubled on a road twenty feet wide. Thus the marching length of a legion of thirty-six hundred men, with its train, was not far from two thousand feet, or doubled, four thousand feet, say three quarters of a mile. If the legion was marching manipulatim in “column of fives,” the cohorts would take up over three thousand feet, and with baggage added would stretch out somewhat more ; on a bad road, a full mile.

In presence of the enemy, or in line of battle, the troops were drilled to ploy into column or deploy back into line, to march by the right or left flank, to the front or rear, much as modern armies do. The drill-ground or battlefield manoeuvres of a legion were almost identical in principle and performance with our own, the variation relating mainly to the greater depth of the Roman lines, the difference in arms and the absence of artillery. The manoeuvres of one of our civil war brigades, in a line of battalion-columns doubled on the centre, would not be much unlike those of a legion.

The legion in presence of the enemy also marched, when the ground permitted, in a sort of square formed by a van and rear with baggage between and heavy flanking columns on each side of the train. The square was quickly formed for the march from the legion in line. Cohorts 1, 2 and 3 kept straight on. Cohorts 5 and 6 formed column left in front so as to face outwardly when coming to a front. Cohorts 4 and 7 formed column right in front. Cohorts 8, 9 and 10 formed line to the rear, and then broke by the right of cohorts or maniples to the rear and marched behind the baggage.

These last were then in such order as readily to form line to the rear and complete the square.
The baggage was thus enclosed in the centre; its length might somewhat modify the formation of the marching square. We hear of the Roman army marching over what we know must have been very difficult ground in this formation. It is not to be presumed that accurate order was preserved when the ground was wooded or much cut up.

Caesar is as perfectly exact in his use of terms to describe these manoeuvres as if writing a book of tactics. And the Roman “drill-regulations” had been established for generations and modified only as requirements from age to age dictated. Still there are many minor points which cannot be positively elucidated. The cavalry wings of four hundred men marched by turmae forty feet wide, taking up, without baggage, nearly five hundred feet length of column. The train probably added half as much. The ranks of the turmae column were also doubled in narrow ways, just how is not known. They must often have been obliged to reduce front and thus lengthen the column. A body of four thousand horse, such as Caesar had in Gaul, with baggage, would take up, in simple column, nearly a mile and a half ; doubled up, three miles.

All this was naturally subject to precisely the same difficulties which are encountered by every army in the field. And the more wooded and broken the territory the less accurately could the “tactics ” be conformed to. In Gaul, no doubt, there was constant and great deviation from the regulations.

Romans on the March

The day’s march (iter) was reckoned from camp to camp. A day of rest was customary after every three or four marches. Each night, or whenever a stop was made, the camp was fortified. This intrenching practically took the place of our outpost system, besides being something else. The legions usually fought with their camp in their rear. If they came across the enemy on the march, they stopped, half the men fortified a camp, while the others protected them, placed the baggage in it and then fought, — provided, indeed, they could so long fend off the enemy. The ordinary day’s march was from fifteen to eighteen miles, theoretically supposed to be done in five summer hours, nearly seven of ours, generally from early morning to noon, there being thus enough time left for camping.

The step (gradus) was two and one half Roman feet long; the route step one hundred to the minute ; the quick step one hundred and twenty. This is about our own standard. The pace (passus) was two steps, from right heel to right heel. The Roman foot was nine tenths of ours.

The average Roman march was no greater than that o£ modern days. Some exceptional marches were remarkable. Caesar left Gergovia at daybreak to move on Litavicus, marched twenty five Roman miles, struck him and brought him to reason the same day, marched back twenty five miles, and the next day reached Gergovia before daybreak, the legions having rested three hours during the twenty four, and six more having been consumed in watching the enemy under arms. The only superior to this march which can be quickly recalled is that of the Spartans to Marathon, one hundred and fifty miles in three days. Crassus marched to Join Ceasar, who was moving to the assistance of Cicero, and made from midnight to nine A. M. twenty five Roman miles. In the Zeta raid, Caesar’s legions marched thirty-six miles from before day-break to nightfall, capturing a town and fighting four hours in retreat on the way. We do not know just what periods of rest were allowed during the day’s march. We rest usually ten minutes every hour. On occasion marches were made without baggage. It goes without saying that the Roman marches were subject to the same interruptions, difficulties and delays as our own. Muddy roads and rivers were as common.

The Vanguard

A vanguard (primum agmen) was usual, and consisted of the bulk of the cavalry and light troops, scouts, staff-officers and camp men supported by some cohorts without baggage. The main body followed. A guard brought up the rear. The duty of the van was to attack and hold the enemy, if met, so as to enable the main body to form; to reconnoitre the front’ and advance flanks; to select and stake out a camp. The cavalry Caesar sometimes kept with the main body when he did not deem it reliable, or when one of the flanks had to be protected from danger of attack. Light troops alone were used as vanguard when the cavalry was on other duty.

The rear-guard in marches towards the enemy had no duties except to keep order at the tail of the column and pick up stragglers. The main body marched in simple column or in battle order by the flank, according as the enemy was far or near, or the land was friendly or inimical. An army of five legions, with baggage, eighteen to twenty thousand men, all told, took, in a forty-foot wide order, from two to two and a half miles of length, with ranks doubled twice as much. In practice, the column was much more strung out than this when the roads were not good.

Out of presence of the enemy, the train of each legion accompanied it for greater convenience; in his presence, the train was kept together in one body. When moving on the enemy, the bulk — say three quarters — of the main army was in front, then the train, then the remainder as baggage and rear-guard.
In battle order the legions were not intended to march any distance. This order was used only in the immediate vicinity of the enemy. When Caesar moved against the Usipetes and Tenchtheri, each legion is supposed to have marched deployed into three columns at deploying distance. There were thus fifteen parallel columns for the five legions. The whole could at once deployed forward into line. The legionaries had their helmets on, their shields uncovered and their weapons ready ; the baggage had been left in the camp.

We remember that on the march the legionary had his helmet hanging on his chest, his shield in a case, and his plumes, and other insignia of rank or corps, wrapped up. If suddenly attacked the men must lay down their baggage, prepare and put on their badges and get ready their weapons. At the river Sabis the Romans had to fight without this preparation.

The marches in retreat were conducted on reverse principles, with similar precautions. The baggage went with the vanguard, followed by the bulk of the army ; then came a strong rear-guard. The marches in squares were made through an enemy’s territory, or in times of insurrection, or when the enemy was on every side. Sometimes the square was composed of the whole army; sometimes each legion marched in square. On every front of such a square, cavalry, bowmen and slingers were thrown out as skirmishers. The baggage was in the centre of the one large square, or that of the legion in the centre of each legionary square.

Flank marches were made in battle order, with baggage on the side opposite the enemy, or between the lines if there were more than one. Such marches were not usually made for any great distance. In the open field the legions so marching were protected by flankers. In a valley a stream might serve to protect the column. Caesar marched up the Elaver in battle order by the flank for several days.

The order of march was changed daily, to equalize the labour of the legionaries. Caesar’s legions crossed rivers with ease, wading fords up to the waist, breast and even neck. They carried no ammunition ; their armour and weapons could not be spoiled. Bridges took as a rule too long to build; Caesar preferred fords when available. If the river was deep and the current rapid, a line of cavalry was stationed above and below, the first in an oblique line to break the current, the last to catch men who were carried down. Fords were now and then passed in line of battle, as at the Thames.

Bridges were as quickly built as today. The absence of pontoon-trains was no apparent hindrance. They were built of boats picked up along the river, as often as on piles; whichever was at the moment handier. But once did Ceasar in the Gallic War cross a river directly in the face of the enemy. This was the Thames. Bridgeheads usually protected both ends of a bridge.

Ceasar kept to the uniform ancient habit of drawing up his legions for battle on the gentle slope of a hill, so that they might have the advantage of the descent for casting their pila as well as for the rush upon the enemy. The utmost reliance was put upon the initiative so as to make the first shock a telling one when possible. The legions were wont to await the advance of the enemy to within two hundred and fifty paces (if, indeed, he would advance), then at the common step to move upon him, and when within half this space to take the run (cursus). The distance was not great enough to wind the men, even in their heavy armour. The first two ranks held their spears aloft in readiness and hurled them at ten to twenty paces from the enemy. If the volley produced sufficient gaps, falling to with the sword the legionaries would penetrate into these and have the enemy at their mercy. In case the enemy was brave and determined, the legions often remained longer at javelin-casting distance and used their spears only, the rear ranks advancing through the front ranks to hurl their pila in their turn. The ten ranks could thus deliver five heavy volleys of javelins, having exhausted which, the first line of cohorts drew the sword or allowed the second line to advance in its turn. It sometimes occurred that the enemy was so rapid as to leave no time to hurl the pila, and the legionaries set to at once with the gladius. But this was rare. The light troops kept the fighting line supplied with javelins, collected from those hurled at it. Or again the two first lines, after casting their pila, would at once close in with the sword. When exhausted they would allow the next two ranks to come forward, hurl their pila and use the sword; and thus the ranks worked successively, — hours being often consumed in this array of duels between the individuals of each fighting line.

The old legionary always pushed his enemy with his bossed shield. He was so well armed and so expert that he could sometimes fight all day without receiving a wound. He was physically strong and could gradually force the enemy back in places by sheer pressure and thus make gaps into which he could penetrate with deadly effect. During battle, few legionaries were either killed or wounded, — but when one line bioke, the other could cut it to pieces.

In case the enemy awaited the Roman advance, this was conducted in similar manner. The first ranks were sustained by the backward ones in such a manner that there was a never-ceasing motion in each cohort as those who still held their pila in their turn advanced to hurl them; yet there was no loss of formation, as the space occupied by each man gave ample room to advance and retire within the body of the cohort. The second and third lines remained at a suitable distance in the rear, — two hundred feet or more, — ready to support the front line by advancing into or through its intervals. The second line was ordered forward when the first line ceased to gain a perceptible advantage over the enemy. All the lines gradually came into action, — the third at the critical moment.

The legion in Caesar’s time excelled because he was at its head. It was not without its disadvantages. The soldiery was brave and were disciplined, but the Roman army was not independent of terrain. The work of the skirmishers, slingers and bowmen, of the auxiliaries, and of the veteran antesignani did not always chime in with that of the legions. The two kinds of infantry would sometimes clash, owing to their different formation. The cavalry was often inefficient, and had to be strengthened by bodies of light infantry placed in the intervals of the turmae. This infantry, when the shock with the enemy’s horse came, could inflict serious damage on it. It helped to steady the movements of the turmae, while protected at the same time from being run down by the enemy’s cavalry. This mixing cavalry and foot is one of the most ancient of devices. In a modified form it has survived to our day. The Roman cavalry was service- able, but at its very best it was not cavalry, such as were Alexander’s Companions or the squadrons of Seidlitz.

The real battle was fought out by the legions. In fact, the legions could be independent of any other troops. Cavalry could attack cavalry; it could cut up broken infantry ; but unbroken cohorts could not be successfully attacked by cavalry except in flank. By a front attack, steady infantry could drive cavalry in every instance. During battle, cavalry was useful only against the enemy’s squadrons. The cavalry and skirmishers were chiefly of use in outpost and reconnoitring duties and in pursuit. In actual battle, the cavalry was not much employed. Since Alexander’s day, it will be seen, cavalry had degenerated.

The cohorts were all-sufficient. When cavalry and light troops were not on hand, the legions found no difficulty in doing all the work themselves. Still they relied on the cavalry and light troops, if present, to protect their flanks while fighting. In case there was grave danger of a flank attack, especially on the right, a fourth line was more than once made by Caesar, the duty of which it was to stand near and defend the threatened quarter.

Habitually the line of cohorts in each legion was threefold as before detailed. This arrangement in an army of six legions in line would give twenty-four cohorts in the first line and eighteen cohorts in each of the others. The third was considered as a reserve not to go into action till ordered by the general. It was on occasion used to sustain the flanks of the legions, or threaten the enemy’s. Its utility was shown at Bibracte and in the battle against Ariovistus. A curious feature of Caesar’ s formation, due probably to Marius, was that the oldest and best cohorts were placed in the front line, and the younger ones in the rear. This was the direct reverse of the principle which in the old legion had ranked the three class-lines as hastati, principes, triarii.

The cavalry was placed as occasion required. As a rule it was on the flanks. It might be posted in the rear, as was the case at Bibracte, because it was not deemed reliable, and in the battle against Ariovistus because the barbarians were protected in flank and rear by their wagons set up as defence, and cavalry against these was useless.

The light troops were only available as a curtain or as skirmishers. In battle they were harmful rather than of use. They do not appear to have been employed to open the action as uniformly as in earlier days, but rather in collateral duties. But they collected darts and kept the legionaries supplied with them.
The line had a centre (acies media) and right and left wing (cornu dextrum, sinistrum). The cavalry wings sometimes first advanced; then legion after legion under the legates in command. This was, as it were, an order of battle with the centre withdrawn. The oldest and most experienced legions were posted on the right and left. If there were no prevailing reasons to the contrary, Caesar preferred to attack with his right in advance, where, like Alexander, he was wont to take his stand. This resulted in a species of oblique order of battle. It was more the result of Caesar’s predilection for personally leading off in action than a definite tactical oblique order, like that of Epaminondas, or as most perfectly exemplified by Frederick at Leuthen. On the signal being blown, the right cohorts at once advanced, those on their left successively following. It was not a tactical advance in echelon with heavily reinforced right flank, but a gradual rushing to battle of the cohorts from right to left. In a measure it had similar results. The best legions* would naturally be stationed on the attacking wing.

The line of cohorts impinged upon the enemy only along part of its front when there were intervals between the cohorts ; and the enemy might and sometimes did penetrate into these intervals, and take the cohorts on the sensitive right flank. But the second line was always on the watch for just this thing, and was ready to correct the evil by a vigorous onset. Caesar’s probable formation, by which the cohorts deployed into a battle order without intervals, eliminated this danger. During the fighting contact there was not only a succession of smaller shocks by the several ranks of each cohort, but the first, second and third lines could deliver their heavier blows in succession, following each other as the tired lines got rest from the advance of those in rear. A hard-fought field was one of incessant motion.

The Phases of Roman Battle

Before the action opened — unless it was precipitated — the general rode the lines and made a short address (cohortatio) to each of his legions, to rouse their martial ardour. He then went to the attacking flank and gave the trumpet signal, which was repeated down the line. The legions of the attacking flank advanced with their battle-cry and the legions on their right or left successively came on in a species of rough echelon. The legions of the first line were followed after a certain lapse of time, perhaps minutes, perhaps hours, by the second and third lines, the cavalry riding forward at the same time to protect the flank or attack the enemy’s cavalry, or — when this was beaten— the flank of the infantry line. When the first line was exhausted, the lines in rear replaced them in places or along the whole; front as ordered, and special bodies of troops were brought up to support decimated legions much as in our own days; moving forward through intervals when these existed, or allowing the broken lines in front to fall irregularly through intervals specially opened for the purpose. Victory being won, the cavalry pursued. Defeat ensuing, the legions withdrew to the fortified camp and re-formed there, the general holding back the enemy with his reserves or the legions least exhausted, and the cavalry. The battles of remote antiquity were very different; the battles of Alexander, Hannibal and Caesar bear more resemblance, in a general way, to our own.

Defensive battles were not fought unless the terrain was especially suitable. The flanks were then leaned on natural obstacles, and the front was protected by wolf -pits or other entanglements. If possible, the army backed on the camp, protected their flanks, and gave the enemy only one approach, in front and up a slope. The camp of Caesar on the Axona, where he invited an attack, was a good sample of this. If the barbarians had crossed the morass in his front, they must have broken ranks in so doing, and Caesar could have charged down on their phalanx with decisive effect, for his flanks were protected by ramparts. At Alesia, the fighting was defensive, coupled with sallies. But in the open field, the Roman strength lay in attack, or in inviting attack and in meeting it halfway.

How many men are in a Legion?

A Roman legion was an infantry unit consisting of heavily armed soldiers, equipped with shields, armour, helmets, spears and swords. In the early republic, the strength of a legion was about 3,000 men; there were 4,800 legionaries in the days of Julius Caesar; the twenty-five legions that defended the empire during the reign of Augustus counted more than 5,000 soldiers.

How many men in a century?

Its basic unit was the century, which comprised eighty men, divided into ten sections (contubernia) of eight, who shared either a barrack room or tent. Six centuries of eighty men formed a cohort, and ten cohorts made up a legion.

When was the first Roman legion raised?

The first reliable records of the Roman army come from the writings of the Greek historian Polybius, who describes the legions of the mid-second century BC.

When did Roman auxiliaries start to be used?

The auxiliaries, or auxilia, were introduced by the emperor Augustus and hailed from all over the Roman empire. They fought alongside the legions, with their precise roles – archer, skirmisher, slinger or cavalry – depending on where they were raised. They were formed into contubernia, centuria and cohorts, each of which had its own Roman commander. Unlike the legionaries, the auxilia were not Roman citizens; citizenship was their reward for completing 25 years of service.

What was the testudo?

One famous battle formation that made use of the scutum was the testudo, or tortoise. The legionaries would lock their shields both in front and above their heads – forming a shell that allowed the whole unit to advance safe from projectiles from above.

Requirements to be a legionary?

All hopeful legionaries had to be Roman citizens, in good physical shape and a minimum of six Roman feet (5ft 9 inches). Though not a requirement, recruits from the countryside were preferred to those from urban areas, as it was thought that they were more accustomed to physical labour and would bear the hardships of war easier.

How many men in a contubernium?

There is ambiguity amongst the classic sources about the exact number of men that made up a contubernium. Probably only 8 men could sleep in the standard 3×3 metre tent at any one time, although two men would have been on watch. 2 colones (army servants or slaves); in both scenarios with two men always on watch. In this major reform to the Roman army, eight fighting men formed a contubernium.

How much were Ceasar’s legionaries paid?

The pay of Ceasar’s legionaries was two hundred and twenty-five denarii (forty dollars) a year. This was about the pay of a day-labourer. His rations and clothing were deducted from his pay, but booty and largesses greatly increased it. His ration is variously stated to have been from one to three pecks of wheat, or other grain, a month; which was probably supplemented by beef , and such vegetables and fruit as the foragers could find.


  • Caesar A History Of The Art Of War Among The Romans by Theodore Ayrault Dodge