A gabion is a cage, cylinder, or box filled with rocks, concrete, or sometimes sand and soil, to be used in civil engineering, road building, and military applications. Gabions are of different types, such as a caged riprap for erosion control while for dams or in foundation construction, cylindrical metal structures are used. In military, earth- or sand-filled gabions protect artillery crews from enemy fire. Gabions in civil engineering stabilize shorelines, stream banks or slopes against erosion. Gabions are also used for retaining walls, temporary floodwalls, and silt filtration from runoff, for small or temporary/permanent dams, river training, or channel lining. Gabions may also be used to direct the force of a flow of flood water around a vulnerable structure. Gabions are also used as fish barriers.