Siege Warfare

[Riffington]

Well, siege weapons would still be useful. After all, that mountain-fortress won't be reduced to rubble all by its lonesome self.

But the mountain fortress isn't useful in the first place, if armies can magically obtain food/water. The point of the fortress was that an invading army would need a constant supply of food, and the forces in the fortress can destroy those supply lines. But if food is easily obtained, then an invading army can just march right past that mountain fortress, telling its defenders that if they would really like to fight they'll have to come out from behind those walls.