 Earlier in the 20th century, taller retaining walls were often gravity walls made from large masses of concrete or stone.Today, taller retaining walls are increasingly built as composite gravity walls such as geosynthetic or steel-reinforced backfill soil with precast facing; gabions (stacked steel wire baskets filled with rocks), crib walls (cells built up log cabin style from precast concrete or timber and filled with soil or free-draining gravel) or soil-nailed walls (soil reinforced in place with steel and concrete rods).For "reinforced-soil gravity walls", the soil reinforcement is placed in horizontal layers throughout the height of the wall.