an idea for fortifying armies and protecting locations and resources.
I was thinking it would be nice if a stack was guarding a location it could start building themselves a little hill fort in a similar manner to how caravan roads improve.
digging in would be continuous as long as the army stack stays in place, 5 turns create a level 1 fort, 10 lv 2 fort, 15 for lv 3 fort etc.
Each level of hill fort would grant some of the same protections that a city would grant, i guess that is mainly a hp boost - probably 10% per hill fort level.
This would be an automatic process, it would require access to some point on the tech tree to do it, and this way we don't need to build outpost in the game.
However, i am not sure what to do about moving armies around making hill forts everywhere. I would suggest having an engineering pack for army units. This unit would be responsible for maintaining the fort, they are after all responsible for building it - if they leave the fort then it either collapses or decays levels over time.