Suddenly there came another burst of that acute fear which had intermittently seized me ever since I first saw the terrible valley and the nameless city under a cold moon, and despite my exhaustion I found myself starting frantically to a sitting posture and gazing back along the black corridor toward the tunnels that rose to the outer world. My sensations were like those which had made me shun the nameless city at night, and were as inexplicable as they were poignant. In another moment, however, I received a still greater shock in the form of a definite sound—the first which had broken the utter silence of these tomb-like depths. It was a deep, low moaning, as of a distant throng of condemned spirits, and came from the direction in which I was staring. Its volume rapidly grew, till soon it reverberated frightfully through the low passage, and at the same time I became conscious of an increasing draft of cold air, likewise flowing from the tunnels and the city above.