Miserere mei, Deus (Allegri)

For roughly a century and a half, the Vatican tried to keep Allegri's Miserere a Sistine Chapel exclusive by the simplest means available: forbidding anyone to write it down. Under Pope Urban VIII, transcribing the piece outside the chapel carried the threat of excommunication, a genuinely severe penalty that nonetheless failed to stop a slow trickle of copies leaving Rome over the decades, some smuggled out by visiting musicians, at least one reportedly obtained by Britain's King Charles I via a diplomatic request.

None of that trickle mattered as much to the piece's eventual wide circulation as a single afternoon in April 1770, when fourteen-year-old Wolfgang Amadeus Mozart, touring Italy with his father Leopold, attended the Wednesday Tenebrae service in the Sistine Chapel and heard the Miserere performed once. That evening, back at his lodgings, he wrote the entire nine-voice piece out from memory. He returned to the Sistine Chapel on Good Friday, when it was performed again, and made small corrections to his transcript against that second hearing, reportedly hiding the manuscript in his hat to check it against the live performance without being seen.

Word of the feat reached Pope Clement XIV, who, by most accounts of the episode, was sufficiently impressed by a fourteen-year-old outwitting a century-old Vatican secrecy rule that he summoned Mozart to Rome and praised him rather than pursuing any penalty, and the transcription was published the following year in London by the historian Charles Burney, effectively ending the piece's long run as a closely guarded Vatican exclusive.

Ask most people what makes Allegri's Miserere unforgettable and they will point to one moment: a treble voice soaring to a piercing top C above the rest of the choir. That note, as familiar as it now is from recordings, is not in Allegri's own surviving notation. What the composer actually wrote down was a plainer, lower-lying setting; the elaborate, high-flying ornamentation that modern audiences associate with the piece grew up gradually as an oral, unwritten performance tradition inside the Sistine Chapel choir itself, singers adding their own embellishments to a piece that was, for most of its history, never fixed on paper for outsiders to check against a fully specified original.

That means the version fourteen-year-old Mozart transcribed from memory in 1770, and the version most modern recordings and performances present as "the" Miserere, are themselves closer to snapshots of an evolving oral tradition than to a single fixed authorial text, in a way not unlike how a folk song can drift across generations of singers even while everyone involved believes they are performing the same piece throughout. Musicologists reconstructing Allegri's presumed 1630s original from what documentary evidence does survive generally produce something notably plainer than the version audiences expect to hear today.

None of this has dented the piece's popularity. If anything, the gap between the historical Allegri and the performance tradition that grew up around his piece over three and a half centuries has become part of the story audiences are told when they encounter it, a rare case of a work's best-known feature being, by most musicological accounts, largely someone else's addition.