The Foundation Stone is the name of the rock at the center of the Dome of the Rock in Jerusalem.
From the Zohar:
and threw it into the depths where it was fixed from above till below,
and from it the world expanded.
It is the center point of the world and on this spot stood the Holy of Holies”.
so is the land of Israel the navel of the world…
situated in the centre of the world,
and Jerusalem in the centre of the land of Israel,
and the sanctuary in the centre of Jerusalem,
and the holy place in the centre of the sanctuary,
and the ark in the centre of the holy place,
and the Foundation Stone before the holy place,
because from it the world was founded.
(from Kedoshim, Chapter 10
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