From Wikipedia:
From 1784 to 1859 the Parisian diapason (concert pitch) rose steadily from 820 to 896 cycles per second, thus Gluck’s French version for haute-contre became increasingly impractical. When Adolphe Nourrit sang the role at the Opéra in 1824 his music was altered. Giacomo Meyerbeer suggested to the French mezzo-soprano Pauline Viardot that she should perform the role of Orfeo. The composer Hector Berlioz was a close friend of Viardot and the leading expert in France on the music of Gluck. He knew the score of “the largely forgotten Italian original as thoroughly as he knew the French”, and agreed to prepare a version of the opera – in four acts – with Viardot’s voice in mind: thus, he did not simply “return to the original contralto version, but rearranged and retransposed the Paris version into keys more suitable for a mezzo”. In his adaptation, Berlioz used the key scheme of the 1762 Vienna score while incorporating much of the additional music of the 1774 Paris score. He returned to the Italian version only when he considered it to be superior either in terms of music or in terms of the drama. He also restored some of the more subtle orchestration from the Italian version and resisted proposals by Viardot and the theatre’s director Léon Carvalho to modernize the orchestration. In the end Camille Saint-Saëns, who was acting as Berlioz’s assistant on the project, did some of the minor rewriting which Berlioz had declined to do.
The Berlioz version was first presented at the Théâtre Lyrique on 18 November 1859 with Viardot as Orphée, Marie Sasse as Eurydice, Marie Ernestine Marimon as L’Amour, Mlle Moreau as L’Ombre, and Adolphe Deloffre as the conductor. The sets were designed by Charles-Antoine Cambon and Joseph Thierry, and the choreography was by Lucien Petipa. (The seventeen-year-old Jules Massenet was the orchestra’s timpanist. During the rehearsals Berlioz had complimented the young player on the accuracy of his tuning.) The production was a popular and critical success, filling the house every night, and was given a total of 138 times by the company.