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This webpage reproduces part of
Gallic War

Julius Caesar

Loeb Classical Library

The text is in the public domain.

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Gallic War

 p595  Appendix A

The Roman Army

The army with which Julius Caesar fought his campaigns in Gaul consisted of legions — four in the first instance, subsequently increased to ten — with auxiliaries attached.

The Legion

The word legio, which originally denoted a "muster" of citizens for infantry service in the force raised year by year for the early wars of Rome, came in due course to denote a "mixed brigade," of infantry and cavalry — to which, by Caesar's time, artillery also was added. A consul's, or pro‑consul's, army consisted of two such legions. Tradition ascribes to one of the Kings, Servius Tullius, the introduction of a property qualification for the levy (dilectus): but, as military service became more and more distasteful to Roman citizens, the property qualification was lowered, and when C. Marius enrolled legions in 104 B.C., at a time of grave disaster and impending invasion, he was glad to accept capite censi — citizens indeed, but poor men and even penniless, who looked to the service for their livelihood. Thus the professional soldier replaced the citizen soldier.

From the beginning of the Republic until the time of the 2nd Punic War (218 B.C.), the infantry establishment of the legion was about 4,200; thenceforward, until the time of Marius, it varied from 4,200 to 5,000, or even 6,000. In Caesar's day the establishment appears to have been about 5,000; but the actual strength of his legions was rarely up to establishment, as may be inferred from B. G. V.49, where he reckons two legions, with some cavalry, as 7,000 men.

 p596  Cavalry

The normal quota of cavalry in a legion was 300. This was composed of Roman soldiers until about 150 B.C.; but the Roman soldier was an infantryman by instinct, and it is significant that in the contingent of allied Italian troops (socii) regularly attached to each legion up to the time of the Social War (90‑88 B.C.), as many infantry were required as in the legion itself, but twice as many cavalry. After the Social War the cavalry consisted almost entirely of foreigners — e.g., in Caesar's army, of Spaniards, Gauls and Germans — commanded partly by officers of their own nationality.


The legions of the Regal Period and of the early Republic appear to have been formed in phalanx — an unbroken line 5 or 6 deep.1 But this formation was too rigid and unwieldy to suit the uneven ground on which much of the fighting of Roman armies in Italy took place. In the age of Camillus, i.e., the beginning of the 4th century B.C., the manipular system began to be adopted. The infantry of the legion were arranged in maniples (manipuli) or double companies, each composed of two centuries (centuriae) drawn up one behind the other, and formed for battle in three lines, quincunx-fashion — :·: This formation gave the individual soldier room to fight, and made it easy to extend or reinforce the first line — in other words, it satisfied the tactical requirements of breadth, depth, and a reserve. This system continued, with some modifications, to the time of Marius; but considerably before this the need of a larger tactical unit than the maniple had been recognised, and the legion had been divided on occasion, if not regularly, into ten cohorts  p597 (cohortes) or battalions of three maniples (six centuries) each. The definite adoption of the cohort as the tactical unit is attributed to Marius; and in the Gallic War of Caesar there are frequent instances of a certain number of cohorts detached for particular duties. There is, however, no clear evidence of the manner in which the maniples were distributed among the cohorts. Two general arrangements appear to be possible:

(1) With the centuries of each maniple, and the maniples of each cohort, drawn up one behind the other thus:

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Or with the centuries of each maniple in line, thus:

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(2) With the three maniples of each cohort in line, thus:

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 p598  Of these formations (1) secures that the immediate reinforcement of the first line is provided by maniples belonging to the same cohort: (2) provides that the three maniples of the same cohort fight side by side in the first instance, or march immediately behind one another in column. Either formation is an acies triplex battle, or an agmen quadratum if turned to a flank for the march in parallel columns preparatory to forming line of battle. For the encounter itself, such intervals as there may have been between maniples of that first line when deployed were probably reduced to a minimum, especially in battles against natives. But the tendency to close in — probably from right to left, as the right was the unprotected side (latus apertum) — sometimes necessitated an order to open the ranks (manipulos laxare: II.25). The maniples retained their standards (signa) after the reforms of Marius; and upon these standards the regular movements of drill and manoeuvre seem to have been pivoted (cf. such expressions in the B. G. as signa inferre, conferre, convertere; ad signa constare).

Of special formations occasionally adopted we may note here the orbis — a "circle" several ranks deep, like the British square, to meet an enveloping attack (cf. IV.37); and the testudo — in which the front rank held their shields in front, the others locked theirs over their heads, opposing a veritable "tortoise-shell" to volleys of missiles (cf. V.9).

The Roman infantry was trained to attack — with a volley of javelins (pila) at short range, followed immediately by a charge and a hand-to‑hand encounter with swords; the second line reinforced or relieved the first at need, and the third likewise, unless it was required, as in the battle against the Helvetii (I.25), to fight a separate action in another part of the field. There is no doubt that Caesar was fully alive to the necessity of adapting his tactics to the occasion; and the readiness and steadiness of his officers and men in sudden emergencies shows how good was their tactical training.

The cavalry of Caesar were formed in regiments or "wings" (alae), stationed, as the name denotes, on the  p599 flanks of the legions, and sub‑divided into troops (turmae) and squads (decuriae). In the battle itself they seldom played an important part: but in pursuit they were often used with effect. The auxiliary infantry (auxilia: also called, from their station, alarii) were organised in cohorts, and were generally employed as skirmishers (levis armatura), or in the use of their special weapons, as archers and slingers. Reconnaissance was carried out by patrols or parties of scouts (exploratores), or by single scouts (speculatores).

Caesar varied his order of march (agmen) according to the nature of the ground and the nearness of the enemy. From II.17 it would appear that the usual order was for each legion to march in column of route, followed immediately by its own baggage-train; and from II.19 that, as the enemy were near at hand, six legions in light order marched first, then the baggage-train of the whole force, and then two legions as rear-guard. A similar march-formation is described in VIII.8 as paene quadratum agmen, which seems to mean a line of columns advancing on a broad front preparatory to battle.


The commander-in‑chief (imperator) of an army of two or more legions was in earlier days one of the consuls, in later days a proconsul or propraetor in charge of a province. The principal staff officer of a provincial governor was his quaestor, whose functions were originally financial: when, as in Caesar's case, the governorship involved military operations as a first necessity, the quaestor combined the duties of Quarter-Master-General and Chief of the Staff, commanding a legion sometimes, and superintending the general administration of the legions in the field. He was, in fact, second in command, ranking above the legati; and in camp his quarters (quaestorium) were next those of the commander-in‑chief (praetorium). In the Gallic War the office was held by M. Crassus and M. Antonius. The legati (staff) of a provincial governor were usually men of senatorial rank, nominated by him  p600 to the number allowed, which in Caesar's case was ten. In the Gallic War the legati served as a General Staff, entrusted from time to time with special duties or separate commands: thus we find them commanding single legions for an engagement of for the winter season, superintending the work of recruiting or shipbuilding. Most prominent among them was T. Labienus (called on one occasion (I.21) legatus pro praetore — that is to say, deputy for the governor and commander-in‑chief): we find him on several occasions holding a large command — of two or more legions, of all the entrenchments, of all the cavalry. The legati of Caesar certainly took precedence of the tribuni militum, of whom there were six to each legion, employed now, it would seem, as commanders of single cohorts, groups of cohorts, or detachments — or even of ships (III.14). Legati and tribuni were summoned to councils of war, and on some occasions the senior centurions (primi ordines) also. These appear to have formed by this time a definite class in the gradation of the 60 centurions in a legion;2 and the chief centurion of all (primipilus) held a responsible and important position. The chief officers of the cavalry and of the auxiliary infantry were called praefecti (commandants), some of whom were chiefs of the nations furnishing contingents. The chief officer of the engineers was the praefectus fabrum.

Special Units

(1) The institution of a cohors praetoria, or commander-in‑chief's bodyguard, dates back to the earliest times, when the commander himself was called praetor; and it was certainly the custom towards the end of the Republican period for a commander to have such a body in immediate attendance. The soldiers who composed it were picked men; and, as a mark of distinction, Caesar declared that the Xth Legion should form his cohors praetoria (I.40).  p601 Under the Empire, the cohortes praetoriae were organised into a definite corps of household troops — the Praetorian Guard.

(2) The evocati, in Caesar's day (cf. III.20), were veterans, time-expired men who renewed their service as volunteers on a special summons. As privileged soldiers, ranking above the legionaries, they were excused ordinary fatigue duties, and were allowed horses on the march (VII.65).

(3) A detachment of troops employed on special duty apart from the legion sometimes had a separate ensign (vexillum) and was called by the same name. (Cf. VI.3540).

4) In Caesar's army there were engineers (fabri), expert workmen who repaired armour, built bridges, looked after siege-material, and performed or superintended other mechanical labours. It is not known how many engineers there were to an army: but it is unlikely that a definite number were attached to each legion.


From the earliest times a Roman army recognised the principle, and followed the practice, of protecting itself with an entrenched camp when it halted after an action or a march. So closely were the day's march and the camp connected, that such expressions as tertiis castris (in three days' march) became common. Sometimes, when an army halted on a battlefield and was about to engage, a part of the force, before the action began, was detailed to entrench a camp.

The ordinary camp of the Republican period was a square, with sides about two thousand feet long, enclosing an area sufficient for the accommodation of two legions, with their cavalry and auxiliaries. The rampart (agger) consisted of the earth thrown inwards from the ditch (fossa) dug all round, with a palisade (vallum) set along the top, made of the stakes (valli) carried by each soldier as part of his field equipment. Between the rampart and the lines was a space (intervallum) of 200 feet. There were  p602 usually four gates — the porta praetoria, in the centre of the front face; the porta principalis dextra and p. p. sinistra, at about one‑third of the distance from the front along the two side faces; and the porta decumana, in the centre of the rear face. From the p. p. dextra to the p. p. sinistra ran the principal street (principia, via principalis), opposite the centre of which, on the side of the porta praetoria, was the praetorium, the headquarters of the commander-in‑chief, with the eagles of the two legions, and the staff on which the red flag (vexillum) was hoisted as a signal for march or battle. On one side were the quaestor's quarters (quaestorium), on the other the market (forum), and beyond on both sides the quarters of the legati and cohors praetoria. In the lower and larger portion of the camp definite spaces were assigned to the legions and the auxiliaries, the latter being nearest to the intervallum on both sides.

For the security of the camp it was usual to post outlying piquets (stationes) of infantry and cavalry, guards (custodes, custodiae) at the gates, and sentries (excubiae, excubitores: or, by night, vigiles, vigiliae) along the ramparts, at general headquarters, and elsewhere.

The ground for the camp was sometimes selected by the general himself, but more often by one of the tribunes, assisted by a party of centurions. Three trumpet calls sufficed to break up camp and resume the march; at the first call, tents were struck and baggage packed; at the second, the baggage was loaded on the pack-animals; at the third, the army marched.

Unless compelled by the sheer necessity of war, Roman commanders did not keep their troops under canvas and in the field during the winter months, but sent them into winter quarters. In the case of Caesar's troops in Gaul, this would generally mean the dispersion of the legions in detachments, to build and fortify cantonments for themselves in or near friendly towns and villages; or, if the inhabitants of a district were still hostile, the establishment of a regular winter camp for one or more legions in some position of strategic importance.

 p603  Assaults and Sieges of Towns

The Roman operations in this connection fall under two main heads: oppugnatio, an assault or a siege leading to an assault; obsidio, a blockade.

In the actual assault of a small or ill‑defended town, part of the troops formed a cordon round the walls, while the rest, with their shields locked over their heads in "tortoise-shell fashion" (testudo), endeavoured to mount the walls in one or more places by means of scaling ladders (scalae), or to break in the gates. When the assault was not immediately practicable — and but few of the Gallic strongholds could be taken off‑hand (ex itinere) — it became necessary to prepare the approaches by formal siege. An inclined plane or ramp (agger), of earth reinforced and revetted with timber, was built from some distance close up to the wall of the place; and along it were pushed one or more wheeled towers (turres ambulatoriae) of several stories (tabulata) high, from which missiles could be discharged at short range upon the garrison, while battering-rams (arietes) were worked below. Large hooks (falces murales) on poles were used to tear down stones from the walls; and artillery (tormenta) of various types (e.g. scorpio, VII.25) hurled stones, pointed stakes, large pikes (pila muraria), or bullets (glandes). Sometimes mines (cuniculi) were dug up to and under the walls. For the protection of the troops engaged sheds or shelters of different kinds (vineae, plutei, testudines, musculi) were used. The defenders, on their part, would attempt to make sorties (eruptiones), to break the heads off the battering-rams or deaden the shock of their impact by fenders, to burn or crush the towers and shelters, to undermine and undercut the ramp, to increase the "command" of their own wall by raising wooden towers upon it, to meet mine by counter-mine, or to make a retrenchment behind a breach in the wall caused by the battery of the besiegers.

If the siege was likely, or was intended, to develop into a blockade, the usual method of the Romans was to surround the town with a continuous field-work (circumvallatio),  p604 strengthened sometimes by towers or redoubts (castella) at intervals, and, if there was danger of an attack from without upon the besieging army (as at Alesia, VII.72), by a second line of entrenchments. The inner line might be further protected by breastworks, chevaux de frise, or such obstacles as are described in VII.73.

Clothing, Arms, and Equipment

The legionary of Caesar was close-cropped and clean-shaven. His clothing consisted of a woollen tunic, a leathern doublet (with metal facings if he could afford them), heavy horseback-nailed sandals (caligae), and a cloak (sagum) of russet. His legs were bare: but in later days breeches (bracae) or puttees (fasciae) came to be worn for campaigns in colder countries like Gaul and Germany. For defence he had a helmet of metal, on which he would set a coloured crest just before battle; a frame (4 feet by 2½) tipped with metal; a greave on his right leg, unprotected by the shield. His weapons of offence were a two‑edged Spanish sword (gladius), about two feet long, which hung on his right side — a sword to thrust with rather than to cut; a dagger, worn on the left side; two six‑foot pikes (pila), carried in the right hand.

On the march he carried his kit (sarcinae) and food in a bundle, on a crutch strapped to his shoulders — called after its inventor mulus Marianus. The heavy baggage (impedimenta) was carried on pack-animals (iumenta), driven by camp-followers (calones). There is no actual evidence that wheeled transport was used by the Romans in the Gallic War; but it is not impossible that, where the roads were good enough, native carts may have been requisitioned for the purpose.

Food and Pay

The staple food of the Roman soldier at this time was wheat. It was issued to him as grain, ground by him in  p605 portable mills, and made into bread or pulse. He was not by choice an eater of meat; and, in view of this, it may be seen that Caesar's skill in organising the cornº-supply was in no small degree responsible for the efficiency of his troops, and the success of his campaigns. Requisitions for corn were made on tributary states, on the ancient principle that war should support itself; and the corn-ration was charged against the pay of the soldier. Good generals allowed their troops no wine; but "vinegar" (posca) was a common drink.

Before Caesar's time the scale of pay was 120 denarii (1,200 asses, about £4) a year; he increased it to 225 denarii (about £7 10s.).

Siege Works

The Roman agger at Avaricum (VII.1724)
(After Colonel Stoffel)

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At a . . . A, B . . . B, the agger is built up in inclined planes, on which towers (T, T) with battering-rams are pushed up to the wall. C . . . C is a terrace, level or nearly level with the top of the wall: from the vinea here a covering fire is kept up to assist the operations. The area D . . . D is not built up, but left at the natural level; from it the troops move by steps, as at E, E to the level C, C.

Roman Works at Alesia (VII.72, 73)
(After Colonel Stoffel)

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Pluteus (VII.73) is the whole screen made up of lorica with pinnae, with vallus behind.

Gallic Wall (VII.23)

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Roman Siege Appliances

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Vinea, mantlet: the sides were covered with skins or wickerwork when required.

The testudo was similar to the vinea, but squarer and more stoutly built, with a sloping roof or shutter on the side next the enemy's walls: it was covered over with hides or other non‑inflammable substances.

The musculus was longer, lower, and narrower than the vinea, forming a covered gallery, pushed up at right angles to the enemy's wall.

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Pluteus, a screen of wickerwork on wheels, generally semicylindrical in form.

The Author's Notes:

1 The word phalanx is used in I.24 of the formation in which the Helvetii attacked, evidently a "mass" of considerable depth.

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2 From VI.40 it is seen that centurions were sometimes promoted for merit from a lower grade in one legion to a higher grade in another.

Page updated: 9 Nov 13