Verdi had become very famous by now, and was asked to compose for the Opéra in Paris. He had to write operas in the French style: operas with five acts and a ballet based on a serious story. None of the operas he wrote at this time for Paris belong to his best works. He was more inspired when writing for the Italian theatres. "Simon Boccanegra" has a complicated plot, but the characters are described beautifully by the music. "Un ballo in maschera" (The masked ball) was about the murder of King Gustav III of Sweden. Again the censors did not like it and he had to change the story to a setting in Boston which rather spoiled the story. In the 1860s his best works were "La forza del destino" ("The Force of Destiny"), written for St Petersburg, "Don Carlos" written for the Paris Opéra, and "Aida" for the new opera house in Cairo in Egypt. "Aida" is considered one of his most perfect works. The first performance was not without difficulties: Verdi was having a long argument with the conductor Mariani who refused to go to Cairo to conduct it. The argument was made worse by the newspapers who accused Verdi of taking Mariani’s girlfriend. This caused a great scandal.