In 1792 King Gustavus III of Sweden was shot at a masked ball, and this was the starting point of Verdi's Un ballo in maschera. But Before the opera could be performed in Rome in 1859, the composer had to deal with a whole series of problems with the censor. It was only when the action was moved to Boston and all reference to real-life figures removed that work could be launched on its triumphant career.