Forts and Resources

[Cainehill]

No. But the castle in B will keep A from drawing from it, likewise B won't be able to draw from A. Not such a big deal if they're both plains with very little resources and each drawing from high resource neighbors, since each could take 40% from, for instance, mountains in C.

A third castle that also bordered C would cause a problem though, as they can't get 120% of C's resources.