Atonality in its broadest sense is music that lacks a tonal center, or key. Atonality, in this sense, usually describes compositions written from about 1908 to the present day where a hierarchy of pitches focusing on a single, central tone is not used, and the notes of thechromatic scale function independently of one another (Kennedy 1994). More narrowly, the term atonality describes music that does not conform to the system of tonal hierarchies that characterized classical European music between the seventeenth and nineteenth centuries (Lansky, Perle, and Headlam 2001). “The repertory of atonal music is characterized by the occurrence of pitches in novel combinations, as well as by the occurrence of familiar pitch combinations in unfamiliar environments” (Forte 1977, 1).

https://en.m.wikipedia.org/wiki/Atonality

Semiramide (Italian pronunciation: [semiˈraːmide]) is an opera in two acts by Gioachino Rossini. The libretto by Gaetano Rossi is based onVoltaire‘s tragedy Semiramis, which in turn was based on the legend of Semiramis of Assyria. The opera was first performed at La Fenice in Venice on 3 February 1823.

Semiramide
Opera by Gioachino Rossini
The composer in 1820, portrait by an unknown painter
Librettist	Gaetano Rossi
Language	Italian
Based on	Semiramis by Voltaire
Premiere	3 February 1823 La Fenice, Venice

Semiramide was Rossini’s final Italian opera and according to Richard Osborne, “could well be dubbed Tancredi Revisited“. As in Tancredi, Rossi’s libretto was based on a Voltaire tragedy. The music took the form of a return to vocal traditions of Rossini’s youth, and was a melodrama in which he “recreated the baroque tradition of decorative singing with unparalleled skill”. The ensemble-scenes (particularly the duos between Arsace and Semiramide) and choruses are of a high order, as is the orchestral writing, which makes full use of a large pit.

After this splendid work, one of his finest in the genre, Rossini turned his back on Italy and moved to Paris. Apart from Il viaggio a Reims, which is still in Italian, his last operas were either original compositions in French or extensively reworked adaptations into French of earlier Italian operas.

Musicologist Rodolfo Celletti sums up the importance of Semiramide by stating:

“(It) was the last opera of the great Baroque tradition: the most beautiful, the most imaginative, possibly the most complete; but also, irremediably, the last”

https://en.m.wikipedia.org/wiki/Semiramide

https://en.m.wikipedia.org/wiki/Carlos_Sanchez-Gutierrez

https://en.m.wikipedia.org/wiki/Circle_of_fifths