Explanation: The African-born Roman Emperor Septimius Severus took an oath at the start of his reign to not execute any Senators, as traditionally the Senate was permitted to oversee their own trials.

He lied.

While Septimius Severus is generally recognized as an intelligent and cultured ruler, it's also noted that he was brutally cunning and ruled as an autocrat rather than a civilian magistrate. Considering his military background in the Legions rather than civilian governance, this is perhaps unsurprising.