According to Polybius, there were three elements of the Roman constitution. These elements included the Consuls, the Senate, and the people. Each group had different powers and responsibilities.
The Consuls were responsible for administration. They had power over all of the magistrates, except the Tribunes. They would bring foreign ambassadors to the Senate and introduce them. They also would bring issues that needed to be discussed to the Senate, and then be sure any orders were carried out. They had complete power in preparing for war and carrying out a war plan.
The Roman Senate was responsible for the treasury. The Senate controlled expenditures, including those dealing with the construction or the repair of buildings. The Senate also was responsible for examining all serious crimes. The Senate determined how foreign ambassadors would be received and what answers would be given to them.
The people also had a role in the Roman constitution. The people would decide cases involving issues of life and death. They also elected leaders and were involved in making and repealing laws. The people also discussed matters of war and peace. They also determined if treaties would be ratified.
This division of power kept any group from gaining too much power.
According to Polybius in his work Histories, the Roman Constitution has three powers; the Consuls, the Senate and the People. Each reserves powers unto themselves separate from the other creating a situation where it is difficult for "even a native" to determine if it is "an aristocracy or democracy or despotism".
The Consuls are the leaders of the Roman legion. When in Rome they are also responsible for the administration of the government. They bring matters before the Senate, run the military, summon popular meetings and enforce decrees upon the population.
The Senate has control of the treasury and controls public investigation of infamous crimes. They also work with the Consuls to send ambassadors abroad and regulate to some degree Italy's role in foreign affairs.
The People reserve control of "honour and punishment". They are the court to decide matters of life and death. They also weigh in on civil matters when the sum of money is "sufficiently serious". The People also have the role of voting for the Senators and voting for declarations of war.
The division of powers was designed to keep any one group from gaining absolute control over the Empire. However, each group maintained almost absolute control in their own areas of concern.