Gustavo III is an opera by Giuseppe Verdi to a libretto begun in early 1857 by the Italian playwright Antonio Somma. Never performed as written, the libretto was later revised (or proposed to be revised) several times under two additional names – Una vendetta in dominò and Adelia degli Adimari – during which the setting was changed to vastly different locations. Eventually, it was agreed that it could be called Un ballo in maschera, the one by which it is known today, but Verdi was forced to accept that the location of the story would have to be Colonial Boston. This setting became the "standard" one until the mid-20th Century. Most productions today locate the action in Sweden.