Daniel looked at the Tor. It was square-floored, each face of the building something less than ten yards wide. Perhaps twenty yards’ altitude separated its gaptoothed parapet from its foundation—a pile of boulders atop a lens of greasy black stone that poked up through the bank. "Shive" was a primeval English word for knee-cap, and Daniel, who had sliced a patella or two from cadavers, could see how the rock had come by its name. Slime and barnacles coated the lower reaches and made it difficult to tell where the natural plinth left off and the man-made work began. The Tor had been built up out of bulky brown boulders probably prised from a quarry upriver, barged down at high tide, and rolled overboard. White mortar held it together. There was but a single door, which looked out onto a silted pool at the terminus of this long gouge that they were fitfully navigating. The threshold was an arm’s length above where the fur of wee crusty creatures and rank weeds gave way to bare, wave-washed stone. So that was where they had built a floor. From the situation of windows (if that was not too grand a term for them) higher up, Daniel estimated there was a wooden platform above, forming an upper storey, and above that a roof, on which lookouts and gunners might stand to look out over, or through, the woebegone parapet.