From the reign of Augustus, major military forces typically were commanded by imperial legates (mostly provincial governors, and thus combining civil and military duties) ultimately responsible to the emperor himself. The province of Africa was an exception in that its senatorial governor commanded its legionary garrison, but only until 37 CE, when Gaius transferred its command to a separate legatus Augusti (Tac. Ann. 4.48). Egypt, of course, was governed by an equestrian prefect who commanded the legions there (as was the case in the Severan province of Mesopotamia).
Individual legions typically were commanded by senatorial officers also known as legates, except for the legions of Egypt and Mesopotamia which were under equestrian praefecti. Commanders of auxiliary alae and cohorts, known as praefecti too, also typically were drawn from the equestrian order and, in contrast to the senatorial officers, might be career soldiers (see Campbell 1994: nos. 102-9 for examples of their careers). Five of the six tribunes, subordinates of the legate in each legion, came from the equestrian order, the sixth being a junior senator.
About 60 centurions of different grades served within each legion (see Campbell 1994: nos. 85-97 for examples of centurions’ careers). They maintained discipline, provided low level command in battle, and commanded detachments away from the main body of the legion. The stereotype of the Roman centurion is of an experienced soldier promoted from the ranks, and certainly a proportion of them came from such backgrounds. However, some were recruited straight into the legionary centurionate from the praetorian guard, and many were recruited directly from wealthier groups in society, including equites (Le Bohec 2000:76-8, based on his study of legio IIIAugusta in Africa; Dio 52.25.7 implies that centurions of equestrian origin were not unusual).
Below the rank of centurion were individuals often termed principales (junior officers within the century with the title optio, tesserarius, or signifer, and some administrative specialists in the legion’s headquarters), who typically received one-and-a-half times normal pay (sesquiplicarii), or double pay (duplicarii). There was also a vast array of technical and clerical specialists within the legion, including surveyors, blacksmiths, weapon makers, and medical orderlies who were known as immunes, because they were exempt from certain fatigue duties (D. 50.6.7 = Campbell 1994: no. 35; in general see Davies 1974).
World History
