Suppose players get to refurbish, repair or straight up build their own fortress. Since it is supposed to be a safe place, a sanctuary, how do I let them protect themselves against magical threats?
In high magic worlds, since both sides are likely to have their own magic users, you can do whatever you want: make the walls stronger, shield against outside magic coming in, erect a giant purple energy dome and so on.
In low magic world it is not much of a concern, since magic is rare and rather weak.
But what can I do if my world falls in the middle?
As I see it, there are three main magical threats:
- Straight up destruction spells.
- Transportation magic (umbrella for teleports and various magics that would let one get inside e.g. digging through solid earth).
- "Social engineering" magics (putting guards to sleep, charming them, disguises, invisibility and so on)
High destructive power of certain spells would probably urge the engineers to build bastion forts rather than traditional medieval castles, in order to mitigate incoming damage. But how can I deal with the other two types?
Just to be clear, I'm talking about military, rather than civil protections. Obviously, high and thick walls are still working pretty well even today, when you are not using them to stop tanks, artillery and bunker-busting missiles.
Anti-magic fields feel a bit like a crutch, rather than a proper solution. And how would magic users do their thing if they own a completely anti-magicked fortress?