What are the three parts of the Roman government?

Thee were not three parts of the Roman government. During the period of the monarchy the king was in charge of the government. The senate was an advisory body for the king. It was not an elected body and was not part of the government. The king appointed the senators. There were also two popular assemblies; the Assembly of the Soldiers and the Assembly of the Tribes (the districts).

During the 482-year period of the Roman Republic the king was replaced by two annually elected consuls who were the heads of the Republic. As the republic developed, four more types of elected officers of state were created: the censors (who carried out the census, enrolled the senators, commissioned public works and oversaw public morality), the praetors (the chief justices), the aediles (who performed many administrative functions) and the quaestors (the treasures). However, the republic did not have a centralised system of government, like a cabinet or an administration. The consuls were not in charge of the other officers of state and each officer acted independently within the remit of their office. The senate continued to be an advisory body. It debated policy matters and influenced policy decisions. However, it was not involved in governance. The popular assemblies voted on bills and elected the officers of state.

During the 503-year period of rule by emperors the emperors were absolute rulers. The government was their court and their bureaucracy. The power of the senate was curtailed. The officers of state became the appointees of the emperor. The consuls were reduced to ceremonial functions. The popular assemblies were either scrapped or emasculated.