When every city tuned its own way

Orchestras today tune to an A of 440 hertz, but for centuries that note was pure anarchy. Every city — sometimes every church — tuned its own way: surviving tuning forks and old organs show the A drifting between roughly 400 and over 460 hertz. The same aria could sit comfortably in one theatre and be unsingable in the next one down the road.

Pitch also kept creeping upwards, because instruments sound more brilliant as string tension rises. The great victims were the singers, forced ever higher; Verdi went as far as campaigning for a lower, uniform pitch.

France imposed an A of 435 by law in 1859, and in 1939 an international conference agreed on today's 440. So the modern A didn't fall from the sky: it's a peace treaty. Signed, of course, after centuries of being out of tune together.