A HISTORY OF DERBYSHIRE power, in pay, privileges, and conditions of service. The legion itself was a brigade of five or six thousand heavy infantry, with no cavalry save a handful used perhaps as scouts or despatch riders. Its rank and file were recruited at least in theory from free Roman citizens, who were sometimes Italian born, but more usually Romanized provincials. Its general was a senator of high rank. Its chief officers were six tribunes young men of some social standing and much inexperience and sixty centurions, who had served up from below and bore the real labours of command. The 'auxilia' were differently constituted. The unit was a comparatively small body of 500 or (not seldom) 1,000 men, called a ' cohort ' if infantry and an ' ala ' if cavalry. The men were levied, not always voluntarily, from the less quiet and civilized lands of the Empire, and not least from Britain. As a rule they were not citizens of Rome, but subjects, devoid of the Roman franchise till they received it as a reward on their discharge from active service. Only the officers were Romans, and these ranked naturally far below the general of the legion. The whole auxiliary status was that of an inferior grade of soldiers. Both these classes of troops were stationed together in those provinces in which frontiers were perilous or populations unquiet. Probably, though direct evidence on the point is lacking, they were employed in about equal numbers or with a small preponderance of ' auxilia.' That is, if the province contained three legions, it would contain also fifteen or twenty thousand auxiliaries. But they were not habitually quartered together. Legions and auxilia were provided with two different kinds of permanent cantonment. The picture presented by any ordinary province having a large army consists of two elements, a few large fortresses and a number of small forts. The fortresses (hiberna) were occupied by the legions. Each fortress covered some 50 or 60 acres, and (except occasionally in the earlier Empire) accommodated one legion. The forts (castella), on the other hand, were occupied by the 'auxilia.' They varied in size from 3 or 4 to 7 or 8 acres, and were garrisoned generally by single cohorts or ' alas,' but sometimes by smaller forces. The legionary fortresses formed, as it were, the headquarters and the strongholds of the provincial defence. The auxiliary forts were dotted about the country according to need. Some stood at intervals along important roads running through disturbed and difficult districts. Others guarded strategic points. Others, not the least important, constituted the cordon along the frontier which kept the province safe from external foes. The disposition of the British army well exemplifies the system. Three legions were cantoned in three fortresses the Second Augusta at Caerleon (Isca Silurum), in Monmouthshire ; the Twentieth Valeria Victrix at Chester (Deva) ; and the Sixth Victrix at York (Eburacum). These three legions, therefore, were not posted actually in the thick of the danger. They held strategic positions where the lowlands merged in the uplands and served as headquarters and centres. Corresponding to them were three or four dozen auxiliary forts, some guarding the frontier walls 194
