Just as Qanya grasped the levers which would set the spider scrambling upward once more, there was a sound--one grown hatefully familiar to Dworn since the night before, the feverish buzzing of a number of light high-speed engines. He opened his mouth to hiss a warning, but Qanya too had heard. Instantly she guided the spider-machine as close as possible to the cliff, where the hollowed rock afforded some shelter, and twirled a knob that made it sink down, legs folding compactly. They waited scarcely breathing. A couple of times before they had huddled like this, while flights of the winged enemies whistled over ... but the wingless ones? It seemed impossible that they should be up here, where surely nothing that ran on wheels could travel.... * * * * * The head of a column of the aluminum crawlers came into view, whirring along the ledge with a confident air of knowing where they were going. One by one, the little machines rolled past within a few feet of the crouching spider, hastening on with an uncanny pre-occupation. Dworn saw that, like those he had seen earlier, they were of diverse kinds; and several of them, fitted with claws and racks for transporting booty, were heavily laden now with metal plates and girders carved from some larger machine, a roll of caterpillar tread, a slightly bent axle.... The last pygmy in line, whose afterbody was a bloated tank, gurgled as it jolted by, and trailed an aroma of looted fuel. A few yards beyond the staring watchers, each of the little plunderers pivoted sharply in its turn and without even slackening speed vanished straight into the cliff-face. Dworn and Qanya looked incredulously at one another. "A tunnel!" Dworn grunted in realization. That explained one mystery, at least--how, if the winged and wingless strangers' home base was somewhere above the cliffs, the wheeled machines contrived to forage at the foot of the Barrier. They must have one or more inclined tunnels, bored through solid rock for a distance that staggered Dworn's imagination. Emerging at this level, they had found or constructed a passable road the rest of the way to the valley floor.... Now he noticed that the ledge to which the spider had so laboriously climbed showed signs of being an often-used trail, and the cliffs it skirted exhibited in places the raw marks of recent blasting. "Remember this spot," he told Qanya. "If we should return this same way--there's evidently an easier path down." She said nothing. Dworn wondered wrily if, in her drug beclouded mind, she was aware of how unlikely it was that either of them would be returning from beyond the Barrier. A mad enterprise indeed--a ghost and a zombie, going to seek out a foe whose numbers and whose might grew ever more apparent. The tunnel opening here was clear evidence of engineering resources and skill far beyond that of any of the machine races Dworn knew.