What were the principles of the roman republic?

The Roman Republic did not have a centralised executive, like a cabinet or an administration and the Romans did not elect only the head of the government (such as a president or a prime minister). There were five types of executive officers of state and all of them were all elected annually, except for the censors who were elected every 18 months. Each of these officers of state acted independently within the remit of their office. The two consuls were he heads of the Republic. The praetors were chief justices, the censor had the census (which was more of a property assessment than a head count), oversaw public morality, enrolled the senators and commissioned public works; the aediles performed numerous administrative functions and the quaestors were the treasurers.

The senate was not an elected body. It was composed of patricians (aristocrats) and former executive officers of state. It was not a legislative body either. It was an advisory body. It was a body where matters of policy were discussed and recommendations for the consuls were made. It was the most powerful political body of the Republic.

Rome had three popular assemblies, the Assembly of the Soldiers which gathered all the soldiers; the Assembly of the Tribes which included all Roman citizens who one assembly for each of the tribes) which were Rome's administrative areas); and the Plebeian Council which was the assembly of the plebeians, the commoners. The Assembly of the Soldiers voted on war and peace and elected the senior officers of state (the consuls, the praetors and the censors). The Assembly of the Tribes elected the junior ones (the aediles and the quaestors). Until 82 BC the Assembly of the Soldiers also acted as a court of appeal for capital punishment cases and the Assembly of the Tribes acted as a court of appeal for other cases. The Plebeian Council elected the political representatives of the plebeians, the plebeian tribunes.

In the Early Republic, bills were proposed by the consuls and were voted on by the soldiers gathered in the Assembly of the Soldiers. Later in the Republic the plebeian tribunes became the main proposers of bills and the Plebeian Council became the legislative body.