Blocks, square edges criscrosed every other layer like this #. They've supported everything from building, to large semi trucks in garages with no lifts for yrs.. Just keep the base wider than the top, square and on a flat surface. Out side you can even level the ground out with a flat shovel it its not laying well, gravity pulls straight down when things are plumb. I usually finish off a stack with a 1/8 or thicker plate of alum or steel to prevent the block from some how rolling out if the load should somehow shift.
