Did hector berlioz use plainchant in his final movement of fantastic symphony?

Yes, Hector Berlioz used plainchant in the final movement of his Fantastic Symphony. The movement, titled "Dream of a Witches' Sabbath," features a section called "Dies Irae," which is based on the plainchant melody of the same name. The "Dies Irae" melody is associated with the Day of Judgment in Christian tradition and is often used in requiem masses and other funeral music. Berlioz's use of this melody in the "Dream of a Witches' Sabbath" movement adds to the dark and macabre atmosphere of the piece.