Retaining wall are generally used to retain earth or other material to maintain unequal levels on two faces. The material on the back face is called backfill.
Retaining walls are used in the construction of basement below ground level, wing walls of bridge and to retain slopes in hilly terrain roads.
Retaining wall can be constructed with masonry as well as reinforced concrete. In case of masonry retaining wall, the thickness of wall increases with height because masonry resists the lateral pressure by its weight. Thus it is also called gravity retaining wall.