Comment 9 for bug 741142

As a general remark: at the moment the barbarians are revealed currently when an oremine, a marblemine and either a coal mine or a burners house are build. Then, the bigger military buildings are also enabled for the player.

#5:

1) There is no code in the AI part for making barriers explicit. I agree that this might be useful for scenarios. As a workaround, one could place objects that can not be passed through at a certain place on the map and remove them when the 'seen' action happens. One could also forbid the quarry for the AI for a similar effect.

2) This could be done but would mean to scan at least an area of the map periodically in a Lua coroutine. Alternativly, one could add a new lua hook similar to [1] that is called whenever a (miliary?)building is completed and/or a new field is conquered by a player and/or a new field is revealed to a player. This would require coding but would reverse pushing/polling situation.

[1] http://blog.makezine.com/archive/2010/10/homemade-high-resolution-dlp-3d-pri.html

Actually, 1 and 2 sound quite useful to me but, but both are some work.