Back to the Quadrivium, we may wonder why the stretch to be occupied by five wooden beams is so long and why the floor of the Grand Gallery starts in two stages, by sketching a step leaving a depression 2 cubits long, on the upstream-side of the highest beam.
Having the bridge installed, this floor vacancy had to be filled by five or six additional wooden beams, tapered at the end, parallel to the groove length and resting against the top beam of the mobile bridge.
This little step may raise questions...
I see a dual purpose. The first is a functional one: a block of over five tons, resting on the bridge as it climbs upward, will inevitably cause the beams to sag due to the wood elasticity. This may cause an insurmountable small step at the bridge end.
But the creation of a zone of tapered beams, resting on limestone surface, would solve the problem.
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