Advice on Installing Heavy Fountain?

I have bought a large marble wall fountain that will go toward the back of a raised planter. It weighs some 800 pounds + water and will need a foundation. Here is my thought: dig out the approximately two feet of topsoil to get to the original grade. Lay down about 3-4 inches of coarse gravel for drainage. Build two or three dry stack cinder block foundation columns, making sure the tops are level and aligned with each other. Back fill in the dirt. Place the fountain basin (dimensions about 4 feet x 3 feet) on top. Add back wall and other pieces to back.
The back wall of the fountain should stay in place by sheer weight, but there are three elements that will requires some kind of adhesive. What kind of mortar or adhesive should one use for marble? It nees to blend in with a creamy yellow marble.
Many thanks for any advice you can offer.
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