The consuls' main role was to lead the republic's armies in war, and were endowed with the power to command (imperium) and consult the gods through auspices for this purpose with the more junior praetors, though in the late republic both consuls and praetors mainly had civil functions.
The extent of deference to the senate and its decisions waxed and waned over time but was sufficiently strong during the republican period to find it regularly directing magistrates both on what to do and how to do it.
[3] This influence was especially strong in the administration of public religion, finance, and foreign affairs, including the assignment of magistrates to military commands.
[6] Prior to bringing legislation, however, it was customary for magistrates to give speeches to an informal assembly called a contio where they would try to convince and take feedback from the citizenry.
[7] In times of emergency, a consul could appoint a dictator, who usually exercised absolute command over some duty before resigning on its completion or after six months.
[8] The imperial constitution developed from Augustus' victory in the civil wars of the late first century BC.
He also assumed tribunicia potestas, the power of a plebeian tribune, so to call the senate, propose legislation, and exercise a veto.
More importantly, however, was the dominant influence he had over politics, which made it impossible for other politicians to meaningfully challenge his rule.