This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The Romans seem to have adopted one general method of diminishing or tapering their columns, evidently based on the Ionic and Corinthian shafts of the Greek Orders. In adapting to their own purposes the Greek entasis, they made no allowance for the fact that their columns were frequently used attached to a curtain wall, but seem to have borrowed the Greek method outright, merely simplifying it for their own readier use.
The Doric shaft is that used in the Villa at Albani near Rome; the Ionic column is taken from the Temple of Fortuna Virilis, about 100 B. C.; and the Corinthian is that used on the Pantheon at Rome, about 120 to 124 A. D., although the column itself is of earlier date. These columns are all shown drawn out to the same height, but have a different base diameter.
The Doric column is about 7 1/4 diameters high; and it will be noted that if a base were used with this column, it would bring its height up to 7f diameters, or substantially the eight diameters that has been adopted in modern usage for the height of the Roman Doric column. The fact that this is an early example may help to account for the omission of the base and for the extra weight of the shaft.
The Ionic column from the Temple of Fortuna Virilis is 8 1/2 diameters high. This column, we must remember, in its original use in this Temple, was shown attached to or decorating the face of a curtain wall. The Ionic column used in the second story of the Theater of Marcellus is 9 diameters high.
The column from the Pantheon is about 9 1/2 diameters high, and has a capital excellently proportioned in relation to the shaft.
The shaft from an interior column of the Pantheon has been carefully measured; and its exact diameter at various points of its height is shown at the left in Fig. 141. Its total height (42 feet 6 inches) is divided into 15 modules and 26 parts, from the top of the necking to the bottom of the shaft, between the points shown on this drawing. Each module or semi-diameter is subdivided into 30 parts, and the diminution of the column is carefully figured in these parts. At the right of this drawing is shown a shaft displaying a method which almost parallels that employed on the column from the Pantheon; and this method may, for general purposes, be considered to apply to the tapering of all Roman shafts. The only difference between this modern method and the Classic shaft of the Pantheon is found in the lower one-third of the height, which, in the Classic example, instead of being exactly perpendicular, begins to feel-very slightly -the taper of the upper portion of the shaft. This is a refinement that would ordinarily be too subtile to be appreciated or discerned; and in actual practice in a shaft used on the exterior of a building, it is generally considered best to increase slightly the diameter at this point (one-third of the height of the shaft), instead of diminishing it as was done in this instance, when the Order was used in the interior, at a tremendous size, comparatively isolated, and in such a manner that no great distance could ever intervene between the spectator and the object itself. For all ordinary purposes, the method shown at the right of this drawing is sufficiently distinguished and exact.
Fig. 141. ROMAN CLASSIC COLUMNS.
PLATE LVII. (A reproduction at small size of Portfolio Plate LVII).
ROGERS BUILDING, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, BOSTON, MASS. The Corinthian Order is Used as a Decorative Feature of the Building.