The pilaster is an Architectural elements in classical architecture used to give the appearance of a supporting column and to articulate an extent of wall, with only an ornamental function. In contrast, an engaged column or buttress can support the structure of a wall and roof above.
Pilasters often appear on the sides of a door frame or window opening on the facade of a building, and are sometimes paired with columns or pillars set directly in front of them at some distance away from the wall, which support a roof structure above, such as a portico. These vertical elements can also be used to support a recessed archivolt around a doorway. The pilaster can be replaced by ornamental brackets supporting the entablature or a balcony over a doorway.
As with a column, a pilaster can have a plain or fluted surface to its flattened rectangular profile (cross section) and can be represented in the mode of any of the classical orders. In the giant order pilasters appear as two-storeys tall, linking floors in a single unit.
A pilaster in civil engineering is a vertical rectangular member that is structurally a pier, and architecturally a column. Pilasters are used to decrease the slenderness ratio for the height of masonry walls - L/R<120.