There was a change in the constitution and disposition of the legion after the time of Marius, until the fall of the republic.  The legions were thrown open to men of all grades; they were all armed and equipped alike; the lines were reduced to two, with a space between every two cohorts, of which there were five in each line; the young soldiers were placed in the rear; the distinction between Hastati, Principes, and Triarii ceased; the Velites disappeared, their work being done by the foreign mercenaries; the cavalry ceased to be part of the legion, and became a distinct body; and the military was completely severed from the rest of the State.  Formerly no one could aspire to office who had not completed ten years of military service, but in the time of Cicero a man could pass through all the great dignities of the State with a very limited experience of military life.  Cicero himself did military service in but one campaign.

Under the emperors there were still other changes.  The regular army consisted of legions and supplementa,—­the latter being subdivided into the imperial guards and the auxiliary troops.

The Auxiliaries (Socii) consisted of troops from the States in alliance with Rome, or those compelled to furnish subsidies.  The infantry of the allies was generally more numerous than that of the Romans, while the cavalry was three times as numerous.  All the auxiliaries were paid by the State; their infantry received the same pay as the Roman infantry, but their cavalry received only two thirds of what was paid to the Roman cavalry.  The common foot-soldier received in the time of Polybius three and a half asses a day, equal to about three cents; the horseman three times as much.  The praetorian cohorts received twice as much as the legionaries.  Julius Caesar allowed about six asses a day as the pay of the legionary, and under Augustus the daily pay was raised to ten asses,—­little more than eight cents per day.  Domitian raised the stipend still higher.  The soldier, however, was fed and clothed by the government.

The Praetorian Cohort was a select body of troops instituted by Augustus to protect his person, and consisted of ten cohorts, each of one thousand men, chosen from Italy.  This number was increased by Vitellius to sixteen thousand, and they were assembled by Tiberius in a permanent camp, which was strongly fortified.  They had peculiar privileges, and when they had served sixteen years received twenty thousand sesterces, or more than one hundred pounds sterling.  Each praetorian had the rank of a centurion in the regular army.  Like the body-guard of Louis XIV. they were all gentlemen, and formed gradually a great power, like the Janissaries at Constantinople, and frequently disposed of the purple itself.