Abstract: A hollow, L-shaped plastic block has a protrusion on a first end and a recess on the opposite end which fit together to form a retaining wall. A rod extends between openings in the protrusion and the recess to secure adjacent blocks against lateral movement. Alternating ribs and grooves are formed in two laterally extending surfaces and a horizontally extending surface to reinforce them against bulging and to provide passageways for runoff. Rebar is used to attach the blocks to the underlying and adjacent soil. A hole may be cored in an upper surface, fill selected from the group of sand, soil, rock, cement and water inserted, and the cored plug reattached using spin welding.