A variation on the Romeo and Juliet story and set in 14th century Siena, the libretto is based on Victorien Sardou's 1874 play La Haine (Hatred).

The opera premiered on 15 April 1907 at La Scala conducted by Arturo Toscanini with Solomiya Krushelnytska in the title role.

In the 43 years following the premiere of Gloria he worked on two or three further operas which were never performed and continued to compose chamber and orchestral music.

Like Cilea's earlier operas, L'arlesiana (1897) and Adriana Lecouvreur (1902), Gloria takes its title from its female protagonist and is based on a French play.

The title role was sung by Solomiya Krushelnytska, with Pasquale Amato as her brother Folco and Giovanni Zenatello as her lover Lionetto.

[2] It was revived in Rome and Genoa in 1908 and again in 1909 at the Teatro di San Carlo in Naples with Emma Carelli as Gloria.

The second version of the opera with a revised libretto by Ettore Moschino [it] had fairly extensive cuts made at the suggestion of Ostali, most notably the act 2 confrontation scene between Folco and Lionetto.

[3] It was also given a lavish production in Rome in 1938 with Maria Caniglia and Beniamino Gigli in the leading roles and sets designed by the prominent architect and sculptor, Pietro Aschieri [it].

Although it had a successful German premiere at the Dortmund Stadttheater that same year and outdoor performances at the Castello Sforzesco in Milan and the Piazza Baraccano in Bologna in the late 1930s,[5] Gloria soon fell into obscurity once again.

In the midst of angry protests from Aquilante, Bardo, and the other Guelph noblemen, Lionetto's cloak falls away, revealing not only that he is armed but is also a famous condottiere of the Ghibelline forces known as "Il Fortebrando".

The woman urges her to accept Lionetto as her husband which would bring about peace between the two factions and prevent the destruction of Siena, "Prigioniera d'amor" (Prisoner of love).

Gloria is torn between her love for Lionetto and loyalty to her father and the people of Siena, "O mia cuna fiorita" (O my flowered cradle).

Gloria's brother Bardo enters her chambers in disguise and berates her for betraying her people and causing the death of their father who has just been killed defending Siena.