This is one symbolism that Dan Brown did not dare to delve upon. Even Mark Booth avoided it in his ‘Secret history of world’. On second thoughts Booth may not have discussed it simply because it is found the world over and is hardly a secret.
It is a symbolic representation of the formless bearer of this universe – the oval shaped stone is the Universe and bottom base as the Supreme-power holding it; the eternal cosmic-pillar of fire. The endless sky is the egg with Earth at its base. It also symbolizes the union of the cosmos with energy that resulted in what the physicists call the Big-bang. Perhaps the answer to their quest lies in equating the luminous bulge of the galaxy with the pillar of fire that erupted at Big-bang.
World over it is found in Shiva temples.
I bow to Shiva in consonance with vibrations of the cosmos ~ Om Namoh Shivai.
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Thanks Al for the lovely prompt.