Mozart's Requiem is one thing and Berlioz's is quite another.
Mozart's score calls for 7 pieces of brass and 1 set of timpani along with woodwinds, strings and chorus.
Berlioz's score is for 20 pieces of brass, 16 sets of timpani, 10 pairs of cymbals, woodwinds, strings, chorus and 38 additional brass instruments divided into 4 brass bands.
Mozart's Requiem has balance, form, proportion.
Berlioz has an atomic explosion when all 58 brass instruments play together with 16 sets of timpani during the Dies Irae.
Berlioz had the premiere of his work played at the state funeral of the fallen governor of Algeria--killed during the siege of Constantine.
The war department footed the bill and allowed Berlioz to have over 400 performers in the orchestra and chorus, plus one tenor soloist.
Don't get the wrong idea about the Berlioz Requiem. It has a spirituality to it and the tenor solo in the Sanctus is absolutely beautiful.
However, the omnipotence of the Dies Irae is the main draw to this music.