"This is very easy spying for King Henry." Then she chuckled and added, "Do you hear me, Sir Bertram of Lyonesse? This is very easy spying for King Henry." He made no answer to this gibe, but instead he pushed open the window and carefully surveyed the deep gorge beneath him, for this place was new to him. The night before they had come in by torch-light, over a steep bridge above a black river. The gate into the tower had been opened for them only after long parleying, but he had perceived walls well planned and formidable, great heights in the blackness, and steep, up-and-down streets amongst which they went between strong, stone houses. But he had been aware that this city of Durham was a very strong place. He had been set to sleep that night in a room that faced inwards, and rising in the morning he had seen that just before his face were the great stones of the wall surrounding and fortifying the cathedral. Beneath his gaze were two great towers, pierced with meurtrières, which are slits through which arrows may be shot. Between these two towers was a gateway which he doubted not had a double portcullis, devices for dropping huge stones and rafters upon any enemy that should break through the first portcullis and be captured by the second, so that they would be like rats in a trap. By craning his head out of his window he could see, further along, both to his right and to his left, tall towers in this inner wall, each tower having the appearance of an arch let into its face. But this Sir Bertram was an engineer well skilled in the plans of fortresses, and he knew that what appeared to be arches led up to two slanting holes in each tower, and that the slant of each hole was directed with a fell and cunning purpose. For, to each tower foot a steep and narrow street of the town came up. So, if any enemy should have won the town itself and should come up those streets, then those in the tower would set running down these slanting holes balls of stone weighing two, three or four hundred pounds. By the direction of the slantings, those balls of stone would run bounding down those narrow streets and cause dreadful manglings, maimings and death, principally by the breaking of legs. By those and other signs, this Sir Bertram knew that here, even within the walled town was a fortress almost impregnable and dreadful to assault. This Bishop might well be a proud and disdainful prelate. He was safe, not only from foreign foes, but from his own townsmen, which was not so often the way with Bishops. For it is the habit of townsmen to be at perpetual strife with their Bishops, seeking to break in on them by armed force and to make the Bishops give up their rights and rents and fees in the towns, which if the Bishops could not prevent was apt to render them much the poorer. But at this Prince Bishop the townsmen could never come, so strong was this citadel within the town.