Act I. The marriage between Hélène, daughter of the count of Toulouse and Gaston, count of Béarn, should put an end to the civil war between the two noble houses. The people hope for an alliance under the two families' crossed banners. The count, his brother Roger, Hélène and Isaure, her lady-in-waiting, enter; Gaston and his group arrive. The old enemies shake hands and consent to the marriage.
But Roger, with an incestuous attraction to his niece, burns with jealousy, while many in the group are troubled by dark presentiments. The Apostolic Legate Adhémar de Monteil arrives and names the count supreme commander of the French crusaders in the Holy Land. Solemn oath of allegiance, then all leave. From the nearby chapel we hear the psalms of the nuns. Roger, coming back, is nervous; an unknown soldier arrives: Roger tells him that, of the two kneeling to pray in the chapel, he must spare the one in the tunic and kill the other one. The assassin enters the chapel while some crusaders are kicking up a racket outside. From the chapel come shouts: assassin! But the one to fall is the count, who had given his tunic to Gaston as a sign of peace. The viscount is condemned to exile.
Act II. In a grotto in Palestine Roger, full of remorse, has become a saintly hermit. He gives water to a pilgrim, then rushes to help his companions. Two women, Hélène and Isaure, have come to the Holy Land looking for Gaston. They recognise the pilgrim as Gaston's squire and learn that his master is in Ramla. The women leave and some French crusaders arrive with Adhémar and the count, who, though wounded, has survived the assassination attempt. When Roger returns and sees him, alive and well, he starts, but does not reveal his identity. He asks only to be able to fight together with the crusaders, to expiate an old crime. In Ramla, Gaston is hostage of the Emir; an official drags in Hélène, who has been captured. She tells the infidels that her father's crusaders have not the courage to attack. When they are alone, the young couple embraces. But the Christian army is near; Gaston and Hélène attempt to escape, but are recaptured.
Act III. In the harem where she has been confined, Hélène watches the dance of the concubines. The Emir arrives and tells her that if the crusaders attack, he will have her beheaded. A tumult is heard; the Christians are already inside Ramla. Gaston, who has managed to escape, comes in; the count of Toulouse, victorious, enters with his soldiers, arrests his supposed assassin and despite Hélène's agitation, has her taken away by force. In the square of Ramla, the crusaders gather with the count and the Apostolic Legate: Gaston is condemned to be killed the next day; the young man, in desperation, wants to die right away.
Act IV. In the Valley of Josafat, Hélène passes by Gaston's tent. Adhémar asks the hermit to assist the condemned man. But he is sent out, and Hélène awaits the outcome of the battle. The count arrives, victorious, in the company of a mysterious warrior, with his visor down, who has covered himself in glory: it is none other than Gaston, who reveals his identity and asks for justice. Roger the hermit is brought in, mortally wounded, with just enough time left to explain everything and contemplate with joy the view of liberated Jerusalem before expiring.
The revision of I Lombardi alla prima Crociata, Jérusalem was almost unrecognisable and well removed from its first Italian version after the work done on the libretto by Royer and Vaëz. Verdi signed the contract with the Opéra of Paris in August of 1847 and the opera opened in November of that year. Its success prompted Verdi to carry out a piece of advice given him by Ricordi: he would exact a fine of one thousand francs from any theatre that made any cuts when performing his opera, except for the ballet, which was common practice in French operatic tradition.
Entitled Gerusalemme, the opera was performed at the Scala in Milan in December, 1850, with translation of the French text by Calisto Bassi.