Medivh and Gul’dan have opened the portal that started the first war. Why no one sended some catapults there and destroyed it?
Khadgar destroyed a Dark Portal in WC2.
It’s useless.
Even if you destroy the stone thingies, the rift in space-time remains open.
I wouldn’t say useless but it’s not really worth the effort. If they’re powerful enough to be a threat, they’re probably powerful enough to rebuild the portal.
As Mortis pointed out, they did destroy the Portal. Khadgar ripped it apart stone by stone.
However: Destroying the Portal does not destroy the Rift. And to temporarily seal the Rift required a ritual involving the Eye of Dalaran, the Skull of Gul’dan, and the Book of Medivh. I can’t begin to imagine what it might take to close it permanently.