Scribe and Verdi discussed the Vêpres project as early as 1853 and may have met in person before rehearsals began on November 16, 1854. Evidence regarding Verdi's prosodic concerns, however, is limited to a few extant letters, which also debunk the long-standing assumption that the composer, with his supposedly inferior knowledge of French, readily accepted Scribe's verses without requesting changes. In fact, the letters portray a composer actively involved in structuring the libretto – from its dramatic pace down to details of poetic meter and accentual rhythm – and a librettist aware of Verdi's talent and graciously complying with his wishes.

On at least three occasions, Verdi requested regularly accented verses. Two of these requests refer to choral sections, and in both cases the composer was looking for meters corresponding with two of the most regularly accented Italian equivalents, the vers de sept syllabes (corresponding to the Italian ottonario) and the vers de cinq syllabes (corresponding to the Italian senario). In a letter of June 7, 1854, Verdi elaborated: