In its architectural meaning, the term ORDER refers to the system of columniation practised by the Greeks and Romans, and is employed to denote the columns and entablature together; in other words, both the upright supporting pillars and the horizontal beams and roof, or trabeation, supported by them. These two divisions, combined, constitute an Order; and so far all Orders are alike, and might accordingly be reduced to a single one, although, for greater convenience, they are divided into three leading classes or families, distinguished as Doric, Ionic, and Corinthian.