'Fortress' in the Bible

I saw the vision, and as I watched, I was in the fortress city of Susa, in the province of Elam. I saw in the vision that I was beside the Ulai Canal.

But out of a branch of her roots shall one stand up in his estate, which shall come with an army, and shall enter into the fortress of the king of the north, and shall deal against them, and shall prevail:

But his sons shall be stirred up, and shall assemble a multitude of great forces: and one shall certainly come, and overflow, and pass through: then shall he return, and be stirred up, even to his fortress.

His forces will rise up and desecrate the temple fortress. They will abolish the daily sacrifice and set up the abomination of desolation.