This then is the class of _civitates vectigales_ or _stipendiariæ_ in which the majority of provincial towns are to be reckoned, and which are to be contrasted with a small number of particularly privileged communities, those for instance who had been guaranteed their freedom on the score of earlier alliances or well-attested fidelity, and secondly those which the Romans themselves had constituted as Roman colonies or municipia. Altogether then there are three main divisions of communities included within the provinces: towns with free native constitutions, towns substantially subject, and towns with Roman constitutions.[d] ARMY AND NAVY UNDER AUGUSTUS The higher career of an officer (militia equestris) was open to every Roman citizen possessed of the rank and fortune of a knight or senator. All young knights were not bound to serve, but every man who was ambitious of public career had to fulfil the obligations of military service for five years; after which he was given the command of a cohort or served as a military tribune. Hitherto there had been no separation between military and civil office as far as the upper classes were concerned, and it was the emperor’s intention that there should be none henceforth, otherwise the aristocracy would have almost given up going into the army. We cannot tell with certainty how these young aristocrats who entered the army as officers acquired the necessary technical knowledge, or whether they had to undergo any kind of apprenticeship. The senator was excluded from the army on principle; the knight on the contrary was bound to render military service if he hoped to serve the state in peace or war. His promotion was, of course, in the emperor’s hands. In the time of the republic the people did not make all the appointments, but they had twenty-four posts to dispose of; in the reign of Augustus these _tribuni militum a populo_ were still elected by the people, but this emperor, who had deprived the senate of all means of influencing the army, also took from the people their practically obsolete privilege of electing officers, and about the time of his death the title of tribunus militum a populo ceases to appear in inscriptions. In republican times the supreme command in war had been one of the official duties of the elective magistrates; but under the empire it became the duty and privilege of the imperator, who was represented by his legates in the several divisions of the army. Under Augustus each legion had a legatus legionis, so called to distinguish him from the governors of the imperial provinces (legati provinciæ). The officers of the imperial army were divided according to their social rank in the senatorial and knightly classes.