Part of the description of forcecage states:
A prison in the shape of a box can be up to 10 feet on a side, creating a solid barrier that prevents any matter from passing through it and blocking any spells cast into or out from the area.
If forcecage is cast (in the form of a 10-foot solid box) on a point where an existing spell like sickening radiance is centered, does it break the concentration of the previously cast area-of-effect spell? Or would it trap the AoE effect inside the box?
Best Answer
Interfere with Concentration? No.
Spells do exactly what they say they do. Force cage doesn't cause the target to lose concentration. While you can't cast out of the force cage, a spell already cast wouldn't be interfered with unless the other spell requires a constant line of sight... Witch Bolt would be broken by force cage, for instance, but not because of concentration.
Or would it trap the AoE effect inside the box? Sorta...
You could cage off the area to prevent people from entering into the area of effect, but it would not stop the effect from happening in that area.