Praefectus aerarii militaris

The aerarium militare was the military treasury of Imperial Rome. It was instituted by Augustus, the first Roman emperor, as a "permanent revenue source" for pensions (praemia) for veterans of the Imperial Roman army. The treasury derived its funding from new taxes, an inheritance tax and a sales tax, and regularized the ad hoc provisions for veterans that under the Republic often had involved socially disruptive confiscation of property.

The praefecti aerarii militaris (singular praefectus) were the three prefects who oversaw the treasury.

The Imperial biographer and historian Suetonius saw the aerarium militare as a response to the uncertainty of retired military men in need who might be inclined to support a coup or foment unrest. The professionalizing of the army during the Republic created the new problem of veterans, since earlier in Rome's history male citizens served short-term to confront specific threats or carry out seasonal campaigns, and then returned to their normal occupations. The solution in the late Republic had been to settle veterans in colonies in conquered territory, or on ostensibly public land in Italy that in fact had been used by the aristocracy for personal gain; the redistribution of this land by military commanders such as Marius and Pompeius was resented by the elite as a popularist currying of favor among the lower ranks of society. A state-supported benefit helped redirect the former soldier's loyalty from his immediate commanding officer to the Roman state as a whole. Under Augustus, monetary grants replaced land redistributions, and were better received by the upper classes, who nevertheless complained about new taxes.

Augustus included the aerarium militare among the accomplishments in his Res Gestae, the commemorative autobiography published posthumously throughout the Empire. In addressing the Senate on the subject, Augustus had stated his intention to provide for military personnel from enlistment through retirement.

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