Mark each of two 4-by-8-foot sheets of foam into eight 1-by-4-foot strips. Cut each 1-inch-thick sheet using a utility knife against the straight edge.
Glue the 16 strips together with gorilla glue. Lay one 1-foot-by-4-foot strip on a flat surface. Cover the top with gorilla glue. Press the second strip of foam on top, lining up the edges. Continue to apply glue and stack layers of foam until all 16 strips are piled on top of one another.
Place the foam in a standing position so it is 4 feet high. Wrap a 5-foot length of small rope loosely approximately 12 inches from each end. Allow glue to dry completely before continuing.
Measure and mark 4 inches from the top of the foam tower with a fine-point marker. Place a straight edge along the 4-inch mark and draw a straight line around the entire tower.
Draw stone patterns on the four exterior sides of the tower below the 4-inch mark.
Heat up a hot wire foam shaper, and gently press it into the drawn-on stone pattern. Move the foam shaper around gradually to form the stone texture in the pillars. Trace the drawn-on line with the foam shaper to create a concrete top on the pillar.
Paint the faux concrete top using textured gray paint. Fill in all of the lines between the foam stones with the gray paint.
Paint stones different colors to create a more realistic appearance.