This comes to us via Pianogirl, who writes of Georgio Allegri’s Miserere mei, Deus:
For many years, it was thought that Mozart composed this piece because a copy of it was found in his handwriting. It was forbidden for this music to leave the Vatican. Rumor had it — under threat of excommunication — that the choir was forbidden to let the score be taken out of the Chapel, copied, or even seen by any outsider.
On April 11,1770, Wolfgang Amadeus Mozart, age 14, was visiting Rome with his father. The Mozarts attended an evening service at the Vatican and heard Allegri’s “Miserere.” That same night — after just one hearing — young Wolfgang transcribed the piece from memory, and the Mozarts returned three days later to check Wolfgang’s transcription against a repeat performance of Allegri’s music. The elder Mozart thought that letting people know about this feat of memory might be good “P.R.” for young Wolfgang.
In any case, the Mozarts were not excommunicated, and Roman society was suitably impressed when they learned of the teenager’s remarkable musical talent.
The first time I ever heard this, I just wanted to prostrate myself in prayer and penance.