The dangerous terrain aside, the narrow pathway into Sidgler prevented any army from displaying their true potential. Small waves of a hundred-people going against the castle was nothing but suicide.
When Lorist led his convoy through the duchy, he had them disguised as merchants and successfully conquered Xith Castle. He left it in the care of the second highness's troops. But right after the duke mobilized Seamountain Legion from Sidgler, the second highness left after a few days because it was only good for defending against outside threats rather than inside ones. While Xith Castle was hard to take from the outside of the valley, the opposite was true from the inside. The reason was that the duke was afraid he would be trapped in the valley if anybody managed to conquer the castle and hold there.
The duke renovated the castle heavily over the past few years and made a simple citadel into a triple-walled contraption. The company he had originally stationed in the castle was also increased to a full regiment. Even if one managed to conquer the first wall, the troops defending the castle would still be able to put up resistance from the second and third walls. It was precisely because of Duke Madras's confidence in his castle that he allowed his most elite unit, Seamountain Legion, to head to the frontlines to give the Northland bumpkins a long due lesson and chase them back across the river.