pediment, in architecture, the triangular gable end on a building of classic type or a similar form used decoratively. It consists of the tympanum, or triangular wall surface, enclosed below by the horizontal cornice and above by the raking cornice, which follows the slope of the roof. In Greek architecture the pediment usually contained sculpture when used with the Doric order. In the Roman and Renaissance styles it was used also as a purely decorative motif, chiefly over doors and windows; the upper profile of the pediment was sometimes of segmental shape. In later Renaissance and baroque design the pediment often took on fantastic shapes, notably in the variants of the broken pediment, in which the two sides of the raking cornice do not join. The scrolled broken pediment was a favorite in American Colonial work, especially in doorways and over mantels.

In geology, any relatively flat surface of bedrock (exposed or lightly covered with soil or gravel) that occurs at the base of a mountain or as a plain having no associated mountain. Pediments are most conspicuous in basin-and-range-type desert areas throughout the world, but they also occur in humid areas. In the tropics, the surfaces tend to be covered with soil and obscured by vegetation. Many tropical river towns are situated on pediments, which offer easier building sites than the steep hillsides above or the river marshes below.

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