A pilaster is a slightly-projecting flattene column built into or applied to the face of a wall. In discussing Leon Battista Alberti's use of pilasters, which Alberti reintroduced into wall-architecture, Rudolf Wittkower wrote, "The pilaster is the logical transformation of the column for the decoration of a wall. It may be defined as a flattened column which has lost its three-dimensional and tactile value."