The walls of the big trench steadily became higher and steeper, to the point where they'd had to be shored up with pilings and retaining walls of split logs. Then all of a sudden the walls curved together above him, forming an arch. Jack reined the horse in and stared forward into a dark tunnel, large enough for two or three horsemen to ride abreast. It was cut into the foundation of a steep hill that rose abruptly from generally flat land. Through a momentary parting in the drifting clouds of smoke, Jack looked up and saw the mutilated face of the great bastion looming up above him, and glimpsed the high roof of the Emperor's Palace beyond and above that.