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, standard-bearers,
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 men for 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 slingers 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 1000 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 1000 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 in 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 | II. | Augusta (Isca Silurum, now Caerleon). |
| ” | VI. | Victrix (Eburacum, York). |
| ” | XX. | Valeria Victrix (Deva, Chester). |
| Lower Germany ( = lower Rhine) | I. | Minervia (Bonna, Bonn). |
| ”” | XXX. | Ulpia Victrix (Vetera, Xanten). |
| Upper Germany | XXII. | Primigenia (Moguntiācum, Mainz). |
| ” | VIII. | Augusta (Argentorate, Strassburg). |
| Pannonia (Danube to Semlin) | X. | Gemina (Vindobona, Vienna). |
| ”” | XIV. | Gemina (Carnuntum, Petronell) |
| ”” | I. | Adiutrix (Brigetio, near Komorn). |
| ”” | II. | Adiutrix (Aquincum, near Budapest). |
| Upper Moesia (Middle Danube) | IV. | Flavia (Singidūnum, Belgrade). |
| ”” | VII. | Claudia (Viminacium, Kostolac). |
| Dacia (now Transylvania) | XIII. | Gemina (Apulum, Karlsburg). |
| Lower Moesia (Lower Danube) | I. | Italica (Novae, Sistov). |
| ”” | XI. | Claudia (Durostorum, Silistria). |
| ”” | V. | Macedonica (Troesmis, Iglitza). |
| Asia Minor (Cappadocia) | XV. | Apollinaris (Satala, Armenian frontier). |
| ”” | XII. | Fulminata (Melitene, on upper Euphrates). |
