no point in walls outside then...

[hwoo]

Bought the game and love it. My last game had two big open areas that I wanted to narrow down. Not for tower defends but only to limit them to one direction of attack as it was impossible to defend the way it was.

First raid and they burn it down. So im pretty much forced underground :-/

[ShadowDragon8685]

Actually, walls are quite useful. You just need to use them right.

Raiders burn walls under two circumstances.
1: If they cannot draw a path to a building to destroy. (And they only path to buildings, not colonists,)
2: if they get a "burn of opportunity" because the path they're following to a building to destroy takes them parallel to a wall.

The raiders, like your colonists, tend to prefer a faster path if they can find it. The trick, then, is to build a concrete highway that leads them to your killbox and keeps them away from moving parallel to your walls. This is complicated by the fact that it's important to build a concrete slab two tiles thick outside of your walls, as a firebreak.

Build highways away from the walls that lead in through narrow openings, hopefully into a grave-lined killbox. Build your concrete firebreaks, and line them with rubble to make them unattractive pathing targets. And, lastly, line the rubble firebreaks with blasting charges set far back enough that they won't damage the wall, and if someone is climbing over rocks to set fire to a wall, invoke the Chunky Salsa Rule. (Build your 'splosives two tiles away from one another, to get a guaranteed kill.)