Un ballo in maschera

Un ballo in maschera (A Masked Ball) is an Italian opera in three acts. The music was written by Giuseppe Verdi. The libretto was written by Antonio Somma. It is based on Eugène Scribe's "Gustave III ou Le Bal Masqué". 
The opera was first performed at the Teatro Appollo in Rome, on February 17, 1859. One of Verdi's richest middle-period works, it relates the events surrounding the assassination of King Gustav III of Sweden, but because of censorship, the story was transposed to 17th century Boston, with Gustav becoming an English governor, Richard of Warwick. Nowadays, most productions present the opera in its original Swedish setting.