Short answers, pulled from the story.
Jérusalem is a grand opera in four acts by Giuseppe Verdi, premiered at the Salle Le Peletier in Paris on the 26th of November 1847. It is an adaptation and partial translation of his 1843 Italian opera I Lombardi alla prima crociata.
Jérusalem received its premiere at the Salle Le Peletier in Paris on the 26th of November 1847, given by the Opéra. The US premiere followed at the Théâtre d'Orleans in New Orleans on the 24th of January 1850.
The French libretto for Jérusalem was prepared by Alphonse Royer and Gustave Vaëz on Eugène Scribe's advice. The pair had earlier written the libretto for Donizetti's most successful French opera, La favorite.
Jérusalem moves the story to French involvement in the First Crusade of 1095 to 1099, changes characters' names from Italian to French, and turns Arvino into the baritone Count of Toulouse. Several roles were deleted, including the leading tenor part of Oronte, and Verdi added a ballet and new music while reshaping the structure.
Jérusalem follows Gaston, who is framed for the attempted murder of the Count of Toulouse by the Count's jealous brother Roger and is exiled during the First Crusade. After the battle for Jerusalem, the dying Roger confesses to the plot and restores Gaston's honor.
Verdi accepted his first commission from the Paris Opéra in 1847 after director Léon Pillet had invited him in November 1845 and February 1846. Adapting I Lombardi let him try his hand at grand opera without writing something entirely new, a strategy Donizetti and Rossini had used for their Paris debuts.
Giuseppina Strepponi, a singer Verdi met around 1842 who sang the first Abigaille in Nabucco, lived near Verdi in Paris and helped him with the music. A handwritten love duet in Verdi's autograph score for Jérusalem contains alternative lines in her handwriting and in his.