As most are aware I believe the pyramids evolved from practical structures
which served to irrigate the desert. Possibly the Great Pyramid was constucted
because the water level was dropping all along the desert on west side of the Nile
which threatened all the irrigation. In this scenario the pyramid was primarily a
pump which could push water up many miles away.
More likely these were simply four sided dams which were overbuilt. They were
constructed at a time when the written word was new and all the old ways were
giving way to a new world where people specialized in narrow fields. It would have
been obvious to anyone who considered it that progress was going to become much
more rapid and people would become far more focused and specialized. The new
educated men would have knowledge primarily in increasingly narrow areas. The
old ways and old knowledge would not survive this transition. They wanted to leave
a monument not only to themselves but the human spirit. They wanted to leave a
symbol that man was much more than tool for digging in the dirt or designing rockets
which would take us to new worlds of dirt to scratch.
They knew the size and weight of the Earth. They could manipulate numbers and
solve equations though they probably hadn't discovered true algebra. They had a
better understanding of trigonometry. First and foremost they were artisans and
weren't afraid of hard work when there was a goal to achieve.
It was only much later when there was no longer enough water to grow crops that
these areas started to give way to use as cemetaries.
It's very unlikely that their location at the "center of the Earth" is anything more than
mere happenstance. They didn't have maps because they hadn't been able to sail all
over the world. They inscribe the Great Pyramid with their knowledge but it was lost
when the casing stone on which it was written was damaged and partially collapsed in
a 14th century earthquake.
There may have been many reasons it was built but the very fact that they could build
it may have been a very primary reason to do it.