In 1821, at age 18, Berlioz was sent to Paris to study medicine, a field for which he had no interest and, later, outright disgust after viewing a human corpse being dissected. He began to take advantage of the institutions he now had access to in the city, including his first visit to the Paris Opera. He also began to visit the Paris Conservatoire library, seeking out scores of Gluck's operas and making personal copies of parts of them. Despite his parents' disapproval, in 1824 he formally abandoned his medical studies to pursue a career in music. He composed the Messe solennelle. This work was rehearsed and revised after the rehearsal but not performed until the following year. In 1826 he began attending the Paris Conservatoire to study composition under Le Sueur and Anton Reicha. Between 1830 and 1840, Berlioz wrote many of his most popular and enduring works. In 1856 Berlioz visited Weimar where he attended a performance of Benvenuto Cellini, conducted by Liszt. His time with Liszt also highlighted Berlioz's increasing lack of appreciation for Wagner's music, much to Liszt's annoyance. Berlioz was convinced by Princess Sayn-Wittgenstein - with whom he had corresponded for some time - that he should begin to compose a new opera. This work would eventually become Les Troyens, a monumental grand opera with a libretto (which he wrote himself) based on Books Two and Four of Virgil's Aeneid. The idea of creating an opera based on the Aeneid had already been in his mind several years, by the time Sayn-Wittgenstein had approached him, and despite a long disillusionment, his creative flame seems to have remained lit.