i like it

Check radius

Given that the collapse of central or regional authority often led to a decline in irrigation systems (e.g. Mesopotamie) or failure to maintain ♥♥♥♥♥ (e.g. European coastal marshes) which in turn reduced agricultural output, this solution might actually make sense. Where the investment requiring civilization is protected, that decline can be staved off.

Oh, the censorship. D*ke as in coastal defenses, not female romantics from Lesbos.

When you can do this i like this idea

I've made a test version, and the only issue is that it says the Marib Dam is responsible for fertility everywhere.