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.