AIs don't need to know what a river is. All they need to know is it is a tile that requires x points of movement to cross, where x equals how long it takes to ford the river or is derived from a subcalculation that tells them how long it would take the correct unit to reach the river and build a bridge. This makes the AI problem with the river a standard pathfinding problem that nearly every game has had to deal with (what's the shortest distance between point a and point b.)

It's about asking the right question and giving the order at the right time. In this case the right question is just a simple calculation, and computers are good at that.

A complicated AI problem would be predicting that the human was about to drop a river there based on previous in-game behaviours of that player, and have the worker already in the stack.

Right now you can be pretty constrained in the demo if you DON'T roll an Earth magic sovereign; in more than half of my games, my starting location is separated from opponents (and progress) by mountains and sea.

I was tired, I am fully aware that it's a BETA, that's what I meant to say, ftr