The sounding-pipe was an upright bronze chimney pipe two inches in width, embedded within the stonework of the western bearing wall.
It was one of three hundred sound channels installed during the Second Epoch to transmit tidal warnings between the outer watch-posts and the central control galleries. When struck with metal, it produced a sharp, clashing clang. But tapped with the unpolished corner of the Broken Slate. Then, it emitted a deep, hollow thrum that rang through twenty interconnected entry halls like the sound of an iron spear striking a stone shield.
Yan Zhiqiu knelt beside the sounding-pipe in the shadowed crossway of Entry hall 531.
Her fingers were light, rhythmic, tapping the hardened shale against the bronze rim in a rapid, syncopated rhythm: tap-tap-thrum, tap-tap-thrum.
The sound shaking entered the pipe network. It traveled along the floor channels to emerge fifty paces away in the arched entrance of Entry hall 532—an ancient upkeep depot known in Qiao Ming’s charts as the Sump of the Thousand Seals.
Down the main gallery, Lieutenant Lei—one of Zhu Heling’s two surviving strike-commanders—halted his squad of six armored shock-fighters. Lei was a lean, brutal warrior whose face was marked by three upright branding scars from the penal mines of Mount Tian-Zhu. His body wrapped in was heavy greenstone-studded scale armor, wielding a two-handed serrated glaive that hummed with a sickly yellow spirit-current.
