mudbrick

A mudbrick is an unfired brick made of clay.In warm regions with little timber available to fuel a kiln, bricks were generally sun dried. This had the result that their useful lifespan is reduced to around thirty years. Once a building collapsed, new bricks would have to be made and the new structure rebuilt on top of the rubble of the decayed old brick. This phenomenon is the primary factor behind the mounds or tells on which many ancient cities stand.
See more at Wikipedia.org...