This paper presents the senatus consultum ultimum, i.e., the final resolution of the senate passed in moments of extraordinary danger to the Roman Republic. We answer the question what was the legitimacy of such resolutions and indicate their rationale and the effects of their issuance. Senatus consultum ultimum was the most powerful weapon of the Roman senate in the fight against internal political enemies in the late republic, so it needs to be clarified whether the SCU was a legitimate measure to protect the state or it cared only for the political self-determination of the senate and the optimates.