This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
82. When possible, it is best to have the shaft of a column formed in one piece, irrespective of length - that is, a monolith. All the columns in the later portion of the Capitol at Washington are marble monoliths, quarried in Maryland. For a good class of work, if the column is not over 8 feet in height, the shaft is generally so cut, with the cap and base separate.
When a column is to be formed of several pieces, the stones composing the different parts should be very carefully cut, having the abutting surfaces between the cap, base, and shaft perfectly plane and perpendicular to the axis of the column, in order that the pressure may be evenly distributed over the entire surface of the joints. For the latter, nothing but cement mortar should be used, which should not be allowed to come within \ inch of the edge of the joint, in order to prevent spalling the edges of the stones.
If the column is built against a wall, forming what is called a. pilaster, the cap and base should be bonded to the wall, either by extending them into it, or by securing them to it by galvanized-iron clamps, or anchors.
83. An entablature is that part of the structure spanning a porch, or entrance, opening, and supported by columns. All the stones composing the entablature should be well tied together with clamps and anchors, particularly at the outer angles. Porch cornices are sometimes tied to the main structure by long rods enclosed in the mason work, so as to prevent the porch from settling away from the building.
An example of an entablature is shown in Fig. 45, which represents the cornice of a porch. In this, a, a show the two facial stones forming the inside and outside of the entablature; b, the iron clamp, or anchor, holding them together; c, the lower portion of the cornice, showing the dentils; d, the upper part, showing the corona; and e, the bottom member of the architrave, or lower portion of the entablature.