Material Suggestion Needed For Brick Patio
 

I am working on extending my patio. A large portion of our patio does not have a cement slab but white yard rocks. Underneath that is pea gravel then a layer of sand. I want to replace it with bricks.

While digging out the rocks the bottom of the pit consists of all three (big rocks, sand and pea gravel).

What is a good material to lay ontop of this mixture so I can level the ground and set the bricks in. This material will need to be able to keep the bricks in place.

Hard packed dense grade limestone comes to mind.