In theory the Senate was a purely advisory body, but in practice it became a governing body in Rome. It was the legislature, executive and judiciary, all rolled into one. It was a permanent body with ultimate control in Rome and it governed Rome until 133 B.C., virtually unchallenged.
The Senate had been able to obtain this enormous power because of the policy of greedy imperialism pursued by Rome, resulting in vast territorial expansion and a consequent shameful exploitation of the provinces.
The two Triumvirates which were to follow and the presence of Augustus sounded the demise for the Republic, and therefore the rule of the Senate, although, through the Julio-Claudian era, the senate was still very important; with Augustus and Tiberius sincerely interested in maintaining its prestige.
Each emperor had a different relationship with the senate. These relationships combined with the individual attitudes of each emperor resulted in minor changes in practice of the Senate from time to time, although in the end much of the Senate's original duties were restored.
The senate continued to function in the early days of the principate. Even though Augustus had usurped the Senate's functions it handed him much of his authority. This may be attributed to the fact that Augustus controlled the 'real power'. The army.
During Augustus's reign the Senate discussed issues, minted bronze and copper coinage, made laws through the passing of 'senatus consulta', acted as a court of justice and had charge of the Senatorial provinces. Although these duties still stood, Augustus changed their mode of operation by the introduction of the consilium and the use of his 'auctoritas'. As a consequence of the consilium, Cassius Dio states that "it became a practice that all legislation put forward by the emperors is communicated after a fashion through Augustus's select...