Perhaps this has already been done, but what I'd like to mod into my Civ version are forts that have a zone of control around them. That is, they extend your cultural border one tile around them in each direction. This would make forts extremely useful, because you could use them to essentially stake claims in no man's land for future expansion, possibly preventing the AI from settling on a resource you desperately need.

If somebody has already done this, I'd appreciate being pointed to the mod so I can take a look at how they accomplished it and incorporate it into my Civ game.

I'd like to see this as well, but there appears to be a problem with AI pathfinding about it.

Yes i have thought of that Rathelon. Check out fortress seaport improvement. Maybe you would like to help me with this project?

I'd like to see this as well, but there appears to be a problem with AI pathfinding about it.

If it's simply a matter of extending cultural borders, I see no reason why pathfinding should be affected.