Slitherine

I built 3 epiteichismata buildings in a region, costing a total of 9 infrastructure per turn. I don't feel I need them in the region any longer. There was no indication that they were unremovable.

How do I remove them?

It seems you can't, sorry ... But I'm unsure why, they can probably be enabled back for the next patch. In the meantime, if you want to remove them, you would need to edit STRUCTURES.CSV

While we are at disassembling stuff: is there a special reason why palisades cannot be disassembled? Usually not an issue as everyone would make at least a wall of it.
But Dacia has the Dacian forts which provide walls. I Now if you have a fort and a palisade in one region one would want to get rid of the palisade.

So why can't we?

Higher fort levels gives extra garrison so you might not want to dismantle it?

So do higher level Dacian forts. On a disputed frontier you may want to have both (Dacia can build VERY impressive fortifications). But somewhere protected in the inland you just need a wall to keep random revolts in check until the army arrives.

The issue is that deactivate is combined with disassemble, and it would make no sense to deactivate a wall. Also, it would impose on players to deactivate them in safe regions, to optimize infrastructure output, and we don't want the bean-counters fraction of players to feel forced optimizing this kind of thing

Hmm, I see your reasoning but don't agree with it.
Seems like the Dacians will have to wait for future generations to tear down this wall.

While we are talking about walls and Dacians it is wierd that when you cunquer Dacian region then the dacian fortress will just disappear. Or at least it was like this.