gjrk wrote:
"...a Tree of Life (or Fountain of Life), placed in some inaccessible spot (at the end of the earth, at the bottom of the sea, in the land of darkness, on top of a very high hill, or in a "centre")..."

Some fascinating posts (poles) ... food for thought!

Edit:
I was going to comment earlier that six inches wide didn't seem to suggest a totem pole but it seems possible the pole may have had a symbolic purpose only.

Or as someone else suggested (Rhiannon, I think) it could have just acted as a 'plumb-line' to keep the construction centred.