However, the architect/s of the Big Two, as brilliant as he was, had no knowledge of how to build an arch. But, within the lifetime of the architect of Kaphre (allowing for maturity), somehow, someone (he or someone else) perfected the arch which which still stands today in Menkaure's Pyramid.
Straight off. Not in an upper chamber as in the GP which would allow for the passage of time and trial and error in engineering, but underground.
This breakthrough in construction was duplicated in the tomb of Shepsekaf, who it is said, completed Menkaure's Pyramid complex in mudbrick. And then, with this brilliant new architect in tow, decided to ignore all pyramid development and revert to a previous style in the mastaba but still incorporate the arch.
Sounds a little upside down to me.
Is this correct?