'Fortress' in the Bible

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.