A nine-part Miserere, which Mozart is said to have written down from memory after having heard it only once.
Dirk Jaehner <email@example.com> adds: It is true that the young Mozart wrote it down from memory after hearing it one time. His father was very anxious about that because it was forbidden to copy this work. But at that time the Pope himself had given it away a few times. And, freely spoken, this work is not very interesting in its music but in its affection and in its way of performance in the Vatican. Mendelssohn wrote about the performance in a letter that by the time the singing starts the church is completely dark, an one after the other the candles were lit while the choir sings the stanzas of the "Miserere".
Allegri sang tenor at the S. Luigi dei franchesi. At the papal chapel from 1629.
Allegri’s dying day is sometimes also given as 7 February 1652, and on the
picture you can seen on this page it even says he died on 18 February.
Unless someone can convince me of something else, I’ll leave 17 February as the actual day
of his death.