The Messa da Requiem is a musical setting of the Catholic funeral mass (Requiem) for four soloists, double choir and orchestra by Giuseppe Verdi. It was composed in memory of Alessandro Manzoni, an Italian poet and novelist whom Verdi admired. The first performance, at the San Marco church in Milan on 22 May 1874, marked the first anniversary of Manzoni’s death. The work was at one time called the Manzoni Requiem. It is rarely performed in liturgy, but rather in concert form of around 85–90 minutes in length. Musicologist David Rosen calls it ‘probably the most frequently performed major choral work composed since the compilation of Mozart’s Requiem‘

https://en.wikipedia.org/wiki/Requiem_(Verdi)