Mary Beard keeps coming back to the same name: Catiline. Who was he and what did he want? When he conspired to overthrow the Roman Republic in 63 BC, was he acting as a ‘far-sighted radical or an unprincipled terrorist’? Was he a glory-hunting idealist or the victim of senators’ paranoia? And when today’s protesters fill posters and tweets with references to him and his demise, are they employing anything more than empty rhetoric?