The vibration did not travel through the air. It rose through thirty feet of solid limestone bedrock, through the soles of Jon Hale’s heavy work boots, and settled in the marrow of his shins before his ears caught the first note.
It began as a soundless pressure against the skull, like diving to the bottom of the mill pond with eyes shut tight against the silt. Then the stone itself found its voice. A deep, mechanical monotone hum began to pulse beneath the floor of the dry aqueduct, steady as a blacksmith’s bellows but pitched so low that every tooth in Jon’s jaw began to ache in sympathetic rhythm.
Across the flooded catwalk, Master Mason Alden Bram dropped his eight-pound iron framing hammer. The steel head struck a dressed granite flagstone with a dull clink that was instantly swallowed by the subterranean drone. Bram did not stoop to retrieve the tool. He pressed both thick, plaster-crusted palms against his temples, his broad shoulders hunching under his grease-stained leather jerkin as his boots slipped in the pooling canal water.
“Gods of the hill,” Bram roared, though his shout reached Jon as little more than a thin rasp against the vibration. “What is that drone? Is that sapper powder in the lower conduits?”
