Soldier pile and lagging walls, commonly known as soldier piles, are some of the oldest forms of retaining wall systems used in deep excavations. Soldier pile walls have successfully being used since the late 18th century in metropolitan cities like New York, Berlin, and London. The method is also commonly known as the "Berlin Wall" when steel piles and timber lagging is used. Alternatively, caissons, circular pipes, or concrete piles can also be used as soldier piles but at an increased cost. Timber lagging is typically used although reinforced concrete panels can be also utilized for permanent conditions.