Roman Army - Encyclopedia

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ROMAN ARMY. In the long life of the ancient Roman army, the most effective and long-lived military institution known to history, we may distinguish four principal stages. (1) In the earliest age of Rome the army was a national or citizen levy such as we find in the beginnings of all states. (2) This grew into the Republican army of conquest, which gradually subdued Italy and the Mediterranean world. A citizen army of infantry, varying in size with the needs of each year, it eventually developed into a mercenary force with long service and professicnal organization. This became (3) the Imperial 'army of defence, which developed from a strictly citizen army into one which represented the provinces as well as Italy, and was a garrison rather than a field army. Lastly, (4) the assaults of the Barbarian horsemen compelled both the creation of a field force distinct from the frontier garrisons and the inclusion of a large mounted element, which soon counted for much more than the infantry. The Roman army had been one of foot soldiers; in its latest phase it was marked by that predominance of the horseman which characterized the earlier centuries of the middle ages.

So far as we can follow this long development in its details, it was throughout continuous. So unbroken, indeed, is the growth that many of the military technical terms survived in use from epoch to epoch, unchanged in form though deeply modified in meaning, and ordinary readers often miss the diversity which underlies this unchanged-seeming system. The term legio, for example, occurs in all the four stages above outlined. But in each its significance varies. Throughout, it denoted citizen-soldiers: throughout, it denoted also a force which was chiefly, if not wholly, heavy infantry. But the setting of these two constant features varies from age to age. In the first period legio was the "levy," the whole host summoned to take the field. In the second period it was not the whole levy, but one of the principal units into which developing organization had divided that levy; the "legion" was now a body of some 5000 men - the number of "legions" varied with the circumstances, and the army included other troops besides citizens, though they were for the most part unimportant. In the third or Imperial age there were many legions (indeed, a fixed number) quartered in fixed fortresses; there were also other troops, numerous and important, if not yet so formidable as the legionaries. Finally, the legions became smaller units, and the other troops of the army, notably the cavalry, became the real fighting-line of Rome (see Legion).

Table of contents

First Stage

The history of the earliest Roman army is, as one might expect, both ill-recorded and contaminated with much legend and legal fiction. We read of a primitive force of 300 riders and 3000 foot soldiers, in which the horseman counted for almost everything. But the numbers are clearly artificial and invented, while the pre-eminence accorded to the cavalry has no sequel in later Roman history. We reach firmer ground with the organization ascribed to Servius Tullius. In this system the host included all citizens from 17 to 60 years of age, those under 47 for service in the field, those over 46 for garrison duty in Rome. The soldiers were grouped at first by their wealth - that is, their ability to provide their own horses, armour, &c. - into cavalry (18 "centuries"), heavy infantry, a remainder which it would be polite to call light infantry, and some artificers. The heavy infantry counted for most. Armed with long spears and divided into the three orders of hastati, principes and triarii (the origins and real senses of these names are lost), they formed a phalanx, and charged in a mass, while the cavalry protected the wings. The men were enrolled for a year - that is, for the summer campaign; in the autumn, like all primitive armies, they went home. It has been conjectured that about the time of the fall of the kings the normal Roman army comprised some 8500 infantry under 47 years of age, 5000 seniors, 1000 riders and 500 fabri, &c. The evidence for the calculation is unfortunately inadequate, but the result is not altogether improbable, and it may help the reader to realize what "may have been." It must be added that this Servian system is closely connected with the political organization (see Rome, History). Second Stage. - From this Servian army a series of changes which we cannot trace in detail produced the Republican army of conquest. Our ancient authorities ascribe the chief reforms to the half-legendary Camillus, who introduced the beginnings of pay and long service, improved the armour and weapons, abolished the phalanx and substituted for it an open order based on small subdivisions (maniples), each containing two centuries.

Whatever the truth about Camillus, some such reforms must at some time have been carried through, to convert the Servian system into the army which was engaged for nearly three centuries (from 350 B.C.) in conquering Italy and the world. This army broke in succession the stout native soldiers of Italy and the mountaineers of Spain and overthrew the trained Macedonian phalanx. Once only did it fail - against Hannibal (see Punic Wars). But not even Hannibal could oust it from entrenchments, and not even his victories could permanently break its moral. Much of its strength lay in the same qualities which made the Puritan soldiers of Cromwell terrible - the excellent character of the common soldiers, the rigid discipline, the high training. Credit, too, must be given to. the genius of the Scipios and to the more commonplace capacities of many fairly able generals. But the organism itself deserves attention, and, as it chances, we know much about it, mainly from Polybius. Its elements were three: (A) The principal unit was the legion, generally a division of 4500 men-3000 heavy, infantry, 1200 lighter-armed (velites), 300 horse - though sometimes including as many as 6000 men. The heavy infantry were the backbone of the legion. They were levied from the whole body of Roman citizens who had some private means and who had not already served 16 campaigns, and in effect formed a yeoman force For battle they were divided into 1200 hastati, 1200 principes and 600 triarii: all had a large shield, metal helmet, leather cuirass, short Spanish thrusting and cutting sword, and in addition the hastati and principes each carried two short heavy throwing spears (pila), while the triarii had ordinary long spears (see Arms And Armour). They were drawn up in three lines: (I) hastati, (2) principes, (3) triarii; the first two were divided into 10 maniples each (of 120 men, when the legion only counted 4500), the third into io maniples of half the strength. According to the ordinary interpretation of our ancient authorities, the maniples were arranged in a chess-board fashion (quincunx), the idea being that the front row of maniples could retire through the intervals in the second row without disordering it, and the second row could similarly advance. Recent military writers, however, Hastati Principes. Triarii doubt whether this arrangement can be considered workable, and it is possible that our authorities did not really mean what has been supposed. In any case the procedure in fighting seems to have been simple: the front line discharged a volley of pila and rushed in with the short sword - a sequence much like the volley and bayonet charge of the 18th century - and if this failed, the second line went in turn through the same process: the third lino of triarii, armed with spear instead of pi/um, was a reserve. The velites, armed with javelins, were either broken up among the heavyarmed centuries or used as skirmishers or as aids to the cavalry. The 300 cavalry, however, were (it seems) of little account - a natural result if, as we have reason to think, the horses were small and stirrups were not used. The officers of the legion consisted of: (a) Six tribunes, in part elected by the comitia, in part appointed by the consuls, and holding command in rotation. They were either veteran officers, sometimes even ex-magistrates, or young noblemen beginning their career. (b) Sixty centurions, each commanding one century, or, rather, a pair commanding each maniple. They were chosen by the tribunes from among the veteran soldiers serving at the time and were arranged in a complicated hierarchy, by means of which a centurion might move upwards till he became Primus pilus, senior centurion of the first maniple of triarii, the chief officer in the legion. (c) There were also standard-bearers and other under-officers, for whom reference must be made to specialist publications.

(B) Besides the legions, composed of citizens, the Roman army included contingents from the Italian "allies" (socii), subjects of Rome. These contingents appear to have been large: in many armies we find as many socii as legionaries, but we are ignorant of details. The men were armed and drilled like the legionaries, but they served not in legions but in cohorts, smaller units of 400 -500 men, and their conventional positions seem to have been on the wings of the legions. They were principally infantry, but included also a fairly large proportion of cavalry. Despite their numbers, they do not appear to have ranked with the heavy legionary infantry, and they were probably used more as detachments from the main army than as infantry of the line.

(C) Besides legionaries and socii, the Roman army included non-Italian troops of special kinds, Balearic slingers, Numidian horsemen, Rhodians, Celtiberians and others: at Trasimene, for example (217 B.C.), the Roman army included 600 Cretan archers. The numbers of these auxilia varied; probably they were not numerous till the latest days of the Republic.

Composition and Size of Armies in the Second Stage. - According to the general practice, each of the two consuls, if he took the field alone, commanded an army of two legions with appropriate socii. If the two consuls combined their forces, commanding the joint force in rotation (as often occurred), the total would be - according to our authorities - four legions, each of 4200 infantry, the same number of "allied" infantry (in all 33,600 infantry), 1200 legionary cavalry and about 3600 "allied" cavalry =38,400 men. Such, for example, was the Roman army at Trebia (218 B.C.), where (says Polybius) there fought 16,000 legionaries and 20,000 allied infantry. The total number of men in the field could be increased; we even hear of 23 legions serving at one time in the Second Punic War.

Just before this war, in 225 B.C., the total strength of Rome was reckoned at three-quarters of a million, of which about 65,000 were in the field and 55,000 were in a reserve at Rome; of the total, 325,000 were Roman citizens and 443,000 (apparently a rough estimate) were allies. The battle order in normal circumstances was simple. In the centre stood the legionary infantry: on each side of that was the allied infantry: on the wings the cavalry. But sometimes the legions were held in reserve and the brunt (and honour) of the fight was left to the allies. Sometimes, when the army was a double force, one commander's troops fought and the others lay in reserve. Frequently the attack was begun by one wing, as by Caesar at Pharsalus. At Ilipa in Spain Scipio put his Spanish auxiliaries in the centre, his Roman troops on the wings, and attacked with both wings. The chief command of the army fell (as stated above) to the consul, if present, or, if two consuls. acted together, to them in turn. In default of consuls, a proconsul, praetor, or propraetor, in charge of a province, would command.

Development from the Second Stage to the Third. - Towards the end of the Republic many changes began to work themselves out in the Roman army. If Camillus began the system of pay and long service, it was effectually developed by long foreign wars in Spain and in the East. Moreover, the growth of Rome as a wealthy state tended to wreck the old theory that every citizen was a soldier, and favoured a division of labour between (e.g.) the merchant and the military, while the increasing complexity of war required a longer training and a more professional soldier. In consequence, the old restriction of legionary service to men with some sort of private property was abolished by Marius about 104 B.C. and the legionaries now became wholly proletariate and professionals. By a second change, also connected with the name of Marius, the legion was reorganized as a body of 6000 men in 60 centuries, divided into io cohorts instead of (as hitherto) into 30 maniples; the unit of tactical action thus became a body of 600 instead of 120. This was probably an adaptation within the legion of the system of cohorts already in use for the contingents of the socii. Soon after, the extension of the Roman franchise to all Italians converted allies and subjects into citizens, and the socii into legionaries. A fourth change abolished the legionary cavalry and greatly increased the auxilia (C above). And, finally, the appearance of great military leaders in place of civilian statesmen, and of pretenders to a throne in place of patriots, familiarized the world with the notion of large standing armies commanded by permanent chiefs, and at the same time destroyed discipline and military loyalty.

Third Stage

The Imperial Army of Defence. - The evils of the Civil Wars (49-31 B.C.) furnished the first emperor, Augustus, with both the opportunity and the necessity for reforming the army. Disorganization had reigned for twenty years. It was needful to restore loyalty and system alike. Augustus did this, as he did all his work, by adapting the past: yet there is some truth in the view of his latest historian, von Domaszewski, that his army reforms were his greatest and most original work. The main lines of his work are simple. The Imperial army consisted henceforward of two classes or grades of troops, about equal in numbers if unequal in importance. The first grade were the legions, recruited from Roman citizens, whether resident in Italy or in the provinces. The second grade was formed by the auxilia, recruited from the subjects (not the citizens) of the Empire in the provinces, organized in cohorts and alae and corresponding somewhat to both the socii and the auxiliaries (B, C above) of the Republican army. There were also in Rome special "household" troops (see Praetorians), and a large body of vigiles who were both fire brigade and police.

(A) The legion of the Empire was what Marius had left it6000 heavy infantry divided into 10 cohorts: Augustus added only 120 horsemen to serve as despatch-riders and the like. The supreme command was no longer in the hands of the six tribunes. According to a practice which had sprung up in the latest Republic it was in the hands of a legatus legionis, deputy of the general (now of the emperor, commander-in-chief of the whole army) and a man usually of senatorial rank and position. The six tribunes assisted him, in theory: in practice they were now little more than young men of good birth learning their business or wasting their time. The real officers of the legion were the 60 centurions, men who (at least in the early Empire) generally served up from the ranks, and who knew their work. The senior centurion, primus pilus, was an especially important officer, and on retirement frequently became praefectus castrorum, " camp adjutant," or obtained other promotion. Below the centurions were under-officers, standardbearers, optiones, clerks and the like. The men themselves were recruited from the body of Roman citizens (though we may believe that birth-certificates were not always demanded). During the 1st century Italy, and particularly north Italy, provided the bulk of the recruits. After A.D. 70, recruiting in Italy for the legions practically ceased and men were drawn from the Romanized towns of the provinces. After Hadrian, each province seems to have supplied most of the menfor the legion (if any) stationed in it, and so many sons of soldiers born during service (castrenses) flocked to the army that a military caste almost grew up. The term of service was, in full, twenty years, at least in theory, but recruiting was voluntary and when men were short discharges were often withheld. On discharge the ex-legionary received a bounty or land: many coloniae (municipalities) were established in the provinces by certain emperors for the special purpose of taking discharged veterans - according to a custom of which the first instances occur in the latest Republican age. On the whole, the legionary was still the typical "Roman" soldier. If he was no longer Italian, he was generally of citizen birth and always of citizen rank, and his connexion with the Empire and the government was real. Each legion bore a title and a number (e.g. II. Augusta, III. Gallica). The custom of using such titles and numbers can be detected sporadically in the latest Republic, and many titles and numbers then borne by legions passed on into the Empire with the legions themselves. As Augustus gradually became master of the world, he found himself with three armies, his own and those of Lepidus and Antony; from the three he chose certain legions to form his new standing army, and he left these with the titles and numbers which they had previously borne, although that concession resulted in three legions numbered III. and two numbered IV., V., VI. and X. respectively. Similar titles and numbers were given to legions raised afterwards either to fill up gaps caused by disaster or to increase the army. Here, as elsewhere in the Roman and above all in the Augustan system, precedent defied logic.

(B) Besides the legions Augustus developed a new order of auxilia. Auxiliaries (as is said above) had served occasionally in the Republican armies since about 250 B.C., and in the latest Republic large bodies of them had been enlisted in the armies of contending generals. Thus Caesar in Gaul enrolled a division of native Gauls, free men but not citizens of Rome, which ranked from the first in all but legal status as a legion, the "Alaudae," and in due course was formally admitted to the legionary list (legio V.). But this use of non-citizens had been limited in extent and confined in normal circumstances to special troops such as stingers or bowmen. This casual practice Augustus reduced, or rather extended, to system, following in many details the scheme of the Republican socii and veiling the novelty under old titles. Henceforward, regiments of infantry (cohortes) or cavalry (alae), 500 or woo strong, were regularly raised (apparently, by voluntary recruiting) from the non-citizen populations of the provinces and formed a force almost equal in numbers (and perhaps ultimately much more than equal) to the legions. The men who served in these units were less well paid and served longer than the legionaries; on their discharge they received a bounty and the Roman franchise for themselves and wife and children. They were commanded by Roman praefecti or tribuni, and were no doubt required to understand Roman orders; they must have generally become Romanized and fit for the citizenship, but they were occasionally (at least in the 1st century A.D.) permitted to retain tribal weapons and methods of fighting and to serve under the command of tribal leaders, who were at once their chiefs and Roman officers. These auxiliaries provided both the whole of the archers, &c., and nearly the whole of the cavalry of the army; they also included many foot regiments. A peculiar arrangement (to which no exact parallel seems to occur in any other army) was that a cohort of 500 men might include 380 foot and 120 horse and a cohort of woo men or 760 foot and 240 horse (cohors equitata), and an ala might similarly include a proportion of foot (ala peditata). Each regiment bore a number and a title, the latter often derived from the officer who had raised the corps (ala Indiana, raised by one Julius Indus) or, still more often, from the tribe which supplied the first recruits (cohors VII. Gallorum, cohors II. Hispanorum and the like). To what extent recruiting remained territorial is uncertain: after the 1st century, probably, the territorial names meant in most cases very little. The total number of the auxiliary regiments probably varied from time to time and can at present hardly be guessed.

Composition of Armies and Distribution of Troops the Third Stage

If the system of legions and auxilia in the early Empire was novel, the use made of them was no less so. The latest Republic offers to the student the spectacle of large field armies, and though it also reveals a counter tendency to assign special legions to special provinces, that tendency is very feeble.

Augustus ended the era of large field armies: he could, indeed, leave no such weapons for future pretenders to the throne. By keeping the Empire within set frontiers, he developed the counter tendency. That policy exactly suited the military position in his time. The early Roman Empire had not to face - as Britain or France or Germany might have to face to-day - the danger of a war with an equal enemy, needing the mobilization of all its national forces. From Augustus till A.D.250 Rome had no conterminous foe from whom to fear invasion. Parthia, her one and dangerous equal, was far away in the East and little able to strike home. Elsewhere, her frontiers bordered more or less wild barbarians, who might often harass, but could not do serious harm. To meet this there was need, not of a strong army concentrated in one or two cantonments, but of many small garrisons scattered along each frontier, with a few stronger fortresses to act as military centres adjacent to these garrisons.

Accordingly, a system grew up under Augustus and his immediate successors whereby the whole army was distributed along the frontiers or in specially disorderly districts (such as N,W. Spain) in permanent garrisons. On the actual frontiers and on the chief roads leading to them were numerous cohorts and alae of auxiliaries, garrisoning each its own castellum of 3-7 acres in extent. Close behind the frontiers, or even on them, were the twenty-five legions, each (with a few exceptions of early date) holding its own fortress (castra stativa or hiberna) of 50-60 acres. Details varied at different times. Sometimes, where no Rhine or Danube helped, and where outside enemies were many, the frontier was further fortified by a continuous wall of wooden palisades (as in part of Germany, see LIMEs) or of earth or stone (as in Britain, see article Britain, Roman), or the boundary might be guarded by a road patrolled from forts planted along it (as in part of Roman Africa). The result was a long frontier guard covering Britain, and Europe from the German Ocean to the Black Sea, and the upper Euphrates valley, and the edge of the Sahara south of Tunis and Algeria and Morocco, while the wide Empire behind it was little troubled by the presence of soldiers.

The following table shows the disposition of the legions about. A.D. 120 and for many decades subsequently. It would be impossible, even if space allowed, to add the auxiliaries, since the details of their distribution are too little known. But it may be in general assumed that the total number of auxiliaries in any province was little less, and probably rather greater, than the number of legionaries, and the sizes of the various provincial armies can thus be calculated roughly. Thus Britain was held probably by 35,000-40,000 men. Each provincial army was commanded either by the governor of the province or (in a few exceptional cases) by the senior legatus of the legions stationed there: Britain Lower Germany (= lower Rhine) I.

„ XXX.

Upper Germany XXII. VIII. Pannonia (Danube to Semlin) X. XIV.


Flavia (Singidunum, Belgrade). Claudia (Viminacium, Kostolac).

Gemina (Apulum, Karlsburg).

Italica (Novae, Sistov).

Claudia (Durostorum, Silistria). Macedonica (Troesmis, Iglitza). Apollinaris (Satala, Armenian fron tier).

XII. Fulminata (Melitene, on upper Euphrates).

Upper Moesia (Middle Danube) IV.

„ VII. Dacia (now Transsilvania). XIII. Lower Moesia (Lower Danube) I.

Asia Minor (Cappadocia) XV.

. II.


Augusta (Isca Silurum, now Caerleon).

Victrix (Eburacum, York).

Valeria Victrix (Deva, Chester).

Minervia (Bonna, Bonn).

Ulpia Victrix (Vetera, Xanten). Primigenia (Moguntiacum, Mainz). Augusta (Argentorate, Strassburg).

Gemina (Vindobona, Vienna). Gemina (Carnuntum, Petronell). Adiutrix (Brigetio, near Komorn). Adiutrix (Aquincum, near Buda pest).

Flavia (Samosata, on upper Euphrates).

Scythica Ferrata near Antioch (?).(?).

Gallica Fretensis (Jerusalem).

Cyrenaica (Bostra). Trajana (near Alexandria - a disorderly city).

Augusta (Lambaesis). Gemina (Legio, Leon, in N.W. Spain).

The total of legionaries may be put at about 180,000 men, the auxiliaries at about 200,000. If we exclude the "household" troops at Rome, the police fleets on the Mediterranean, and the local militia in some districts, we may put the regular army of the Empire at about 400,000 men. This army, as will be plain, was framed on much the same ideas as the British army of the 19th century. It was meant not to fight against a first-class foreign power, but to keep the peace and guard the frontiers of dominions threatened by scattered barbarian raids and risings. Field army there was none, nor any need. If special danger threatened or some special area was to be conquered - such as southern Britain (A.D. 43) or a little land across the upper Rhine (A.D. 74) - detachments (vexillationes) were sent by legions and sometimes also by auxiliaries in adjacent provinces, and a field force was formed sufficient for the moment and the work.

Change from the Third Period to the Fourth

Two principal causes brought gradual change to the Augustan army. In the first place, the pax Romana brought such prosperity to many districts that they ceased to provide sufficient recruits. The Romans, like the British in India, had more and more to look to uncivilized regions and even beyond their borders. Hence comes, in the 2nd century and after, a new class of numeri or cunei or vexillationes who used (like the earlier auxiliaries) their national arms and tactics and imported into the army a more and more non-Roman element. This tendency became very marked in the 3rd century and bore serious fruit at its close. And, secondly, the old days of mere frontier defence were over. The barbarians began to beat on the walls of the Empire as early as A.D. 160: about A.D. 250 they here and there got through, and they came henceforward in ever-growing numbers. Moreover, they came on horseback, bringing new tactics for the Roman infantry to face, and they came in huge masses. We may doubt if any military system could have permanently stayed this astonishing torrent. But the Empire did what it could. It enlisted barbarians to fight barbarians, and added freely - too freely, perhaps, if there was any choice - to the nonRoman elements of the army. It increased its cavalry and began to form a distinct field force.

Fourth Period

The results are seen in the reforms of Diocletian and Constantine the Great (A.D. 284 - circa 320). New frontier guards, styled limitanei or riparienses, were established, and the old army was reorganized in field forces which accompanied or might accompany the emperors in war (comitatenses, palatini). The importance of the legions dwindled; the chief soldiers were the mercenaries, mostly Germans, enlisted from among the barbarians. New titles now appear, and it becomes plain even to the casual reader that in many points the new order is not the old. The details of the system are as complicated as all the administrative machinery of that age. Here it is enought to point out that the significance of such officers and titles as the dux and the comes (duke, count) lies ahead in the history of the middle ages, and not in the past, the history of the Roman army itself.

War Office, General Staff. - Under the Republic we do not find, and indeed should not expect to find, any central body which was especially entrusted with the development of the army system or military finance or military policy in wars. Even under the Empire, however, there was no such organization. The emperor, as commander-in-chief, and his more or less unofficial advisers doubtless decided questions of policy. But the army was so much a group of provincial armies that much was left to the chief officers in each province. Here, as elsewhere in the Empire, we trace a love if not for Home Rule, at least for Devolution. There was, however, a central finance office in Rome for the special purpose of meeting the bounties (or equivalent) due to discharged soldiers. This was established by Augustus in A.D. 6 with the title aerarium militare, and had, for receipts, the yield of two taxes, a 5% legacy duty and a 1% on sales (or perhaps only on auctionsales). The legacy duty did not touch legacies to near relations or legacies of small amount.


Liebenam, "Exercitus," in Pauly-Wissowa, Realencyclopddie; Von Domaszewski, in Mommsen-Marquardt's Handbuch der romischen Altertitmer (2nd ed., Leipzig, 1884), vol. v, pp. 319-612; H. Delbriick, Geschichte der Kriegskunst, vol. i., 2nd ed. (Berlin, 1907) E. Lammert, "Die Entwicklung der romischen Taktik," in Neue Jahrbilcher fair das klassische Altertum, ix. 100 -28, 169-87; Cagnat's article "Legio" in Daremberg and Saglio, Dictionnaire des antiquites grecques et romaines; E. G. Hardy, Studies in Roman History (London, 1906-9) Th. Mommsen, "Das romische Militarwesen seit Diocletian," in Hermes, xxiv. 195-279.

(F. J. H.)

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