Is there any way for a besieger to find out how many defenders are present in a fortress? In one recent game, I built up a sieging force to storm a castle and was annoyed to find out that there were no defenders inside it.
You can also do this with a scrying spell, such as Eyes of God, Astral Window or Astral Projection. I think - but am not sure - that the Arcosnuffle scrying dominion will do it too.
Playing Ermor, so no spies. I suppose I could always sacrifice a Mound King or something on a storming attempt to see how many and what kind of defenders are present.