Entry hall 432 was a backup machinery chamber hollowed out of the western wall of the Salt-Crusher Crypt, housing the massive balance weight wells that governed the defensive gears of the second and third millstones.
Here, the air was intensely cold, scented with rusted animal fat and ancient hemp-oil. Suspended inside a circular upright shaft six arm-lengths wide hung eight thousand pounds of cast lead ballast. A massive metal tube of dark grey metal four feet in width, held suspended by four heavy wrought-iron chains that passed over grease-packed glowing-bronze pulleys mounted in the ceiling thirty arm-lengths above.
The lead weight was the counter-balance that held the green coarse grey rock bridge in place across the second grinding basin.
As long as the lead metal tube hung suspended in its well, its downward gravity pull was passed through a compound bronze rocker-arm to the underside of the coarse grey rock flat stone slabs. It locked the bridge rigid so that even a loaded stone wagon could cross without bending. But if the main release dog was tripped, the connection was cut instantly. The lead metal tube would plunge forty feet into a high-pressure buffer pool of deep-sea oil, allowing the coarse grey rock bridge to swing downward on its bronze pivot-pins like a falling leaf.
