A rectangular column attached to a wall, partly embedded in it, with one-fourth or one-fifth of its thickness projecting. In classical architecture, a pilaster normally observes the form of one of the architectural orders, such as Ionic or Corinthian, and supports roof beams. The anta of ancient Greece was the direct ancestor of the Roman pilaster. In ancient Roman architecture the pilaster gradually became more and more decorative rather than structural. The fourth-story wall of the Colosseum in Rome contains examples of the Roman use of pilasters. These pillar-like structures were also in the inside walls of Anasazi kivas.