The measurements of the movements of the stars and planets, perhaps?

I guess Kepler got by just using Brahe's observations, but for more modern explorations of gravity there's a boatload of people collecting data.

Well Newton made a huge contribution for sure, but to be able to state his theory he clearly had to use a bunch of math, not all of which came from reknowned mathematicians.

And Einstein didn’t pull out special relativity out of his brain alone. There were years of intense debate about the ether and things I totally forgot by now.

And take something like MOND, there has been tons of small contribution to try to prove / disprove / tweak the theory. If it ever comes out as something that holds, it’d be from a lot of people doing the grind.