Many of the problems of the late Roman Republic came from how a small number of powerful men were able to manipulate power and turn what looked like a somewhat democratic government into an effective oligarchy. In a broader sense, it serves as a lesson about how power can be manipulated in any supposedly democratic constitution.
At the center of power was the Senate, an advisory body of 300 ex-office holders whose decrees (senatus consulta), while not technically laws, carried the virtual force of law. The Senate especially had jurisdiction over officials’ budgets, the technical legality of treaties and laws, and assigning tasks to magistrates (e.g., which ex-officials ruled which provinces and for how long). A ruling principle for the senatorial oligarchy as a whole was to maintain its power as a group without letting any individual members gaining too much power. In addition, the Senate exercised control over three main areas of Roman government: popular assemblies, ex-officials, and religious and traditional ceremonies and procedures.
There were two popular assemblies that the Senate needed to maintain control over. The Comitia Centuriata was originally a military assembly that elected the top officials in Rome (consuls, praetors, and censors) and voted on war and peace. It was originally organized into 193 bloc votes known as centuries, with the rich making up more centuries and thus given more votes. This was to reflect the heavier burden the rich, who could afford full armor, faced in battle. The tribal assembly (Comitia Tributa), which actually passed laws, could only vote on bills proposed by officials, who were also members of the Senate. In both assemblies open ballots where senatorial nobles could keep tabs on how their dependents (clientes) voted.
The primary means of control the Senate had over officials was the fact that after their one-year terms of office, ex-officials all returned to the Senate. This made it unlikely they would go against the wishes of their fellow senators. Therefore, the Senate controlled what laws were proposed and voted on through the consuls and praetors. Even the ten tribunes, who were supposed to protect the rights of the poor through the right to veto laws, had to go back and face the Senate after their year in office.
The Romans were religious, even superstitious people who place great value on omens and doing things by the exact right procedure to keep the favor of the gods. It just so happened the Senatorial nobles also controlled the priestly offices, and virtually all government procedures involved religious rituals that could block or negate government actions. Reinforcing this was the cursus honorum (ladder of honors) that dictated the minimum age, number of times, and order one could hold offices. Every five years, the Comitia Centuriata chose two censors, whose job was to expel unworthy senators and fill empty senatorial seats. Naturally, only senatorial nobles served as censors, making sure that the exclusive club of the Senate contained maintained the purity of its membership and control of the state.