[version_five]

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.

[sircastor]

This is what I was thinking too. The only projects I could figure that have lasted that scale of length are things like cathedrals, the pyramids of Giza, the Great Wall of China, etc. All of these are attached to religion, or at least a supernatural belief in the person driving it.