Three about 6" rings of earth bags (polypropylene tubes filled with lime, clay and sand, which are tamped and cured with water) form the foundation for the walls. They sit on a rubble trench or French drain with two 4" sock-drains in the bottom. Between them is barbed wire to provide some sheer stability, not that much is going to move them, as they are very, very heavy. They keep the bales off the ground, hold in the floor gravel, and provide serious stability to the place.