The great arm, responding to unleashed tension, swung up swiftly, hurling the boulder that lay in the cup against the wall. Against the wall, but not flying over it. At the impact of the boulder, the wall rang like the clanging of a mighty bell. The boulder came tumbling down the slope from which the wall rose. Robots scattered, getting out of the way of the rolling stone, which barely missed the ballista before coming to a halt. Two primitive steam engines, earlier used to haul the ballista into place, stood a little distance off, panting under their head of steam. Conrad plodded slowly to where Horace stood. “It’s no use,” the robot said. “We aren’t going to be able to heave a stone over that wall. It’s the configuration of the wall that defeats us. It flares up and out at the top and we are forced to position the machine too far back to give us the arc we need. And besides, to tell you the honest truth, which I have told you many times before, I fail to grasp the point of it.”
