<P> Early columns were constructed of stone, some out of a single piece of stone . Monolithic columns are among the heaviest stones used in architecture . Other stone columns are created out of multiple sections of stone, mortared or dry - fit together . In many classical sites, sectioned columns were carved with a centre hole or depression so that they could be pegged together, using stone or metal pins . The design of most classical columns incorporates entasis (the inclusion of a slight outward curve in the sides) plus a reduction in diameter along the height of the column, so that the top is as little as 83% of the bottom diameter . This reduction mimics the parallax effects which the eye expects to see, and tends to make columns look taller and straighter than they are while entasis adds to that effect . </P> <P> Most classical columns arise from a basis, or base, that rests on the stylobate, or foundation, except for those of the Doric order, which usually rest directly on the stylobate . The basis may consist of several elements, beginning with a wide, square slab known as a plinth . The simplest bases consist of the plinth alone, sometimes separated from the column by a convex circular cushion known as a torus . More elaborate bases include two toruses, separated by a concave section or channel known as a scotia or trochilus . Scotiae could also occur in pairs, separated by a convex section called an astragal, or bead, narrower than a torus . Sometimes these sections were accompanied by still narrower convex sections, known as annulets or fillets . </P> <P> At the top of the shaft is a capital, upon which the roof or other architectural elements rest . In the case of Doric columns, the capital usually consists of a round, tapering cushion, or echinus, supporting a square slab, known as an abax or abacus . Ionic capitals feature a pair of volutes, or scrolls, while Corinthian capitals are decorated with reliefs in the form of acanthus leaves . Either type of capital could be accompanied by the same moldings as the base . In the case of free - standing columns, the decorative elements atop the shaft are known as a finial . </P> <P> Modern columns may be constructed out of steel, poured or precast concrete, or brick, left bare or clad in an architectural covering, or veneer . Used to support an arch, an impost, or pier, is the topmost member of a column . The bottom-most part of the arch, called the springing, rests on the impost . </P>

What is the top part of a pillar called