First I made a "box" out of 1"x 3" wood and doorskin (thin plywood) materials. Then I glued 2" think styrofoam on to the box.
Then I shaped it using a grated wood-shaving tool that I got fom the hardware store. the handle was made of plastic with a metal grate-costing about a couple of bucks.
Then I took a hot knife to it to make the cracks. I then took some black paint and painted teh cracks first then I painted the the face of the columns with a base coat of solid color. I then used a spray "stone" texture (that yu can get at the hardware store nowadays) over he base coat.