Hector Berlioz's Requiem (_Grande Messe des Morts_, 1837) remains a fixture in the repertoire of choirs and orchestras today. Since 2003, it has been performed in its entirety over one hundred times and has appeared on concert programs spanning the globe: from Russia to the United Kingdom, Finland to the United States, and many locations in between. These performances have, for the most part, been received positively but critics have not always been this kind to Berlioz and his Requiem. Romantic grandiosity, empty dramatic effect, religious insincerity: such are the descriptors that undergird many modern understandings of Berlioz's now-canonic work. Nineteenth-century critics and audiences, however, heard the Requiem in different and compelling ways. This book presenting a broad new musical and social context for understanding the Requiem as Berlioz conceived it and his contemporaries heard it. It asks what, if anything, did nineteenth-century listeners find to be notable about the work, and why? The answers to these questions lie in detailed explorations of Berlioz's relationship to the aesthetics of French sacred music, the theological sublime, and aural architecture. Theatrical as they may have appeared, Berlioz's innovative orchestrations and colossal choral configurations in the Requiem may now be heard as an embrace of the aural possibilities offered by the sounding of the sacred sublime, the physical architecture of French churches, and the interplay between the sacred and the secular.