power and other rights and privileges. The
_imperium_ might be bestowed either by a senatorial decree or through the
acclamation as _imperator_ by a part of the soldiery. Each of these forms
was regarded as valid, but was regularly confirmed by the other. But the
tribunician authority and the remaining powers of the princeps were
conferred only by a decree of the Senate, confirmed, during the first
century at least, by a vote of the Assembly of the Centuries. However,
after the accession of Carus (282 A. D.), the Senate, which could no
longer claim to exercise any authority in the state, ceased to participate
in the appointment of the new ruler. This marks the formal end of the
principate.

*The Senate's loss of administrative power. I. Rome and Italy.* The
constitutional history of the principate is the story of the gradual
absorption of the Senate's powers by the princeps and the supplanting of
the Senate's officers by those in the imperial service. It has been well
said that Augustus aimed at the impossible when he sought to be the chief
magistrate in the state without being at the same time the head of the
administration. He had intended that the Senate should conduct the
administration of Rome, Italy and the ungarrisoned provinces, but, as we
have seen, he himself had been brought by force of circumstances to take
the initial steps in infringing upon the Senate's prerogatives. Not only
did he take over the duties of provisioning and policing the city by
establishing the prefectures of the grain supply and the watch, but he
also assumed responsibility for the upkeep of the public buildings,
streets and aqueducts of Rome, as well as the highways of Italy. These
departments of public works were put in charge of commissioners of
senatorial rank, called curators, whom the princeps nominated. However,
from the time of Claudius equestrian officials, entitled procurators, were
appointed to these departments and became their real directors. Finally,
under Septimius Severus, the senatorial curators were dispensed with.

*II. The aerarium.* Augustus had left to the Senate the control of the
public treasury, the _aerarium_, which was maintained by revenues from the
senatorial provinces and Italy. But when the princeps came to assume
control of those branches of the administration the expense of which was
defrayed by the _aerarium_, it was inevitable that the treasury itself
should pass in some degree under his supervision. An