In short, this work is rarely performed because of the sheer size or orchestra. 100 orchestral players, 500 strong choir,  10 sets of timpani and additional off stage brass sections. 

The tenor aria ‘Sanctus’ was one of Luciano Pavarotti’s calling cards. 

The Berlioz Requiem, also known as the Grande Messe des morts, Op. 5  by Hector Berlioz was composed in 1837. The Grande Messe des Morts is one of Berlioz's best-known works, with a tremendous orchestration of woodwind and brass instruments, including four antiphonal offstage brass ensembles placed at the corners of the concert stage. The work derives its text from the traditional Latin Requiem Mass.