Serious answer is to spend the first 20+ years building a religion out of whatever your idea is. Religion has that kind of demonstrated staying power. And presumably if you have a 300 year vision for something it must have some pretty religious characteristics.

I’d say a combination of other suggestions I see:

1. study past examples

2. focus on a selected group that you can incentivize to donate/invest for prestige or similar

3. use money to pay people that make day to day progress

4. what’s unclear to me is how do you make the project continue after your time, you should probably reserve some of the money to plan for this (back to point 1)

Have you done research on historical precedents for this work? What comes to mind are great works like cathedrals or projects that like the Great Wall of china which was on again / off again over millennia centuries.

In science fiction there’s very long term projects such as in Dune or Foundation which the authors put a great deal of thought into.

You pay them a fair salary, and offer good benefits.

You can’t. They have to incentivize themselves.

What is it you’re thinking of building?

Money.

personal charisma