The supreme authority in Rome was imperium. The Roman Senate granted imperium to certain officials, thus giving them the power to command armies and to interpret and enforce the law. Originally, the Senate gave imperium only to dictators, consuls*, and praetors*, who could exercise it anywhere outside of the city of Rome itself. Imperium was limited to a term of six months for a dictator and one year for consuls and praetors, although the Senate could renew the grant when the term expired. Proconsuls and propraetors, who were the governors of provinces* or heads of certain government commissions, later held imperium. Governors retained this authority only within the boundaries of their provinces, and heads of commissions held power only until their work was completed.
Imperium was graded, or ranked. For example, a dictator had twice as much power as a consul, who held twice as much power as a praetor. In addition, consuls had more authority than proconsuls, and praetors were more powerful than propraetors. These rankings determined the outcome of conflicts between different officials. When proconsuls disagreed, the Senate appointed one to a higher rank by granting him special authority called imperium maius. In 23 B.C., the emperor Augustus was granted imperium maius, enabling him to exercise power throughout the empire, as well as within the city of Rome itself. His term of imperium was renewed at several times during his reign. After Augustus died, emperors were granted imperium maius when they came to power. Imperium maius was occasionally granted to others besides the emperor. This was usually done to create a single military command or to indicate the emperor’s chosen successor. (See also Aedile; Consuls; Dictatorship, Roman; Government, Roman; Magistrates; Praetor; Quaestor; Tribunes.)
* consul one of two chief governmental officials of Rome, chosen annually and serving for a year
* praetor Roman official, just below the consul in rank, in charge of judicial proceedings and of governing overseas provinces
* province overseas area controlled by Rome