There are essentially two ways to tune an instrument (that is tuneable): you can assume that one of the pitches it makes is in tune and then tune the rest of the instrument to the pitch that is in tune OR you can tune all that is tuneable to an exterior reference pitch. I'll call the former relative tuning and the latter absolute tuning, since I'm not sure of the proper terms.
How did musicians do absolute tuning in the Middle Ages - and subsequent times - BEFORE the advent of strobotuners, digital tuners and the like?
For instance, if Beethoven wrote a new piece and said A=440 in the sheet music, how would musicians in the orchestra that were going to play it get their instruments tuned so that A was 440 Hertz?
Offhand, I can only think of two plausible methods: church bells and tuning forks. But even those seem potentially problematic. I'm not sure when the tuning fork was invented, let alone how manufacturers made sure they were accurate, so it may not have arrived on the scene until relatively recently. Church bells would also have issues. Would all church bells in all cities be the same pitch? I see no compelling reason to believe they would be.
I'm at a loss to think of any other sound source that would have been accessible and that MIGHT have a reliable pitch in centuries past.
If tuning forks are a recent invention and church bells are typically different pitches - and especially if the church bell's pitch was unknown - it would seem very likely that performances of a piece of music would sound quite different in each place they were played given that the tuning might vary considerably. Did our ancestors simply live with that or did they have a clever solution?