The vocal score to "Les Troyens" presents the text Berlioz conceived as a great five act opera. During the composition of this work between 1856 and 1858 and up until June 1863, Berlioz perceived "Les Troyens" as one opera. Because of performance difficulties, the composition had to be divided into two operas, "La Prise de Troie" and "Les Toyens à Carthage".
Berlioz began to write the libretto in Paris in April 1856 and completed it on June 26th of that same year. The dramatic material of acts III-V is taken from books 1 and 4 of Virgil's "Aeneid".
The two trojan acts are loosely based on books 1 and 2 by Virgil.
Berlioz wrote in May 1861: "I am sure that I have created a great work, greater and superior to anything I have ever written before".