The Roman Senate's evolution from an advisory council to the Republican era's de facto governing body and then to a largely ceremonial institution under the empire illustrates how political institutions can persist in form while being hollowed out in substance.

The Senate's formal powers in the Republic were advisory: it issued senatus consulta (decrees) that had the force of strong recommendations rather than laws. But its practical power was enormous: it controlled the treasury (the aerarium), allocated provinces to magistrates, conducted foreign policy, declared war and peace, and provided the institutional memory that sustained Roman governance across generations. Membership was for life (unless the censors removed a senator for moral failure), which gave it a stability that annual magistracies lacked.

The Senate's relationship to the emperors oscillated between collaboration and subordination. In the Julio-Claudian period, the relationship was tense: emperors like Tiberius, Caligula, and Domitian treated the Senate with varying degrees of contempt, occasionally prosecuting senators on treason charges (maiestatis) that amounted to political persecution. The Antonine emperors cultivated better relations.

The Senate's transformation into a municipal council for the city of Rome by the late empire reflects the broader shift of imperial governance from Italy to the frontiers. The emperors of the 3rd and 4th centuries AD spent little time in Rome, governing from Nicomedia, Milan, Trier, or Constantinople. The Senate continued to function as a social institution for the senatorial aristocracy and as an administration for Rome itself, but it had ceased to be a political institution in any meaningful sense by the 4th century.