The module: how the writers measured the orders

The writers on the orders do not give their dimensions in feet or metres. They give them as multiples and fractions of one length taken from the building itself, so that the same rules serve for a garden temple and for a cathedral portico. That unit is the module. Vitruvius calls the principle symmetria, the agreement of each part with the whole through a common measure (commensurability). The difficulty for a modern reader is that the writers did not agree on which length to take, or on how to subdivide it.

The lower diameter

The starting point is nearly always the thickness of the column at the foot of its shaft, just above the base. This book writes it D, and states column heights, entablatures and pedestals in it throughout: when it says that Palladio’s Ionic column is nine diameters, it means nine times D, base and capital included. The diameter can be measured on any building, but most mouldings are far smaller than it, so writers who wanted to specify a fillet or an astragal divided the diameter, or half of it, into small parts.

Vitruvius: a different module for each kind of temple

Vitruvius does not use one module for everything. For the Doric he takes the front of the temple at the line of the columns and divides it into a fixed number of parts: twenty-seven for a front of four columns, forty-two for a front of six. One part is the module (the Greek embater). The column is two modules thick, so the Doric module is half the diameter; the column with its capital is fourteen modules high, the capital one module, the architrave one and the triglyphs one and a half (IV.3.3–4). A hexastyle front 42 feet wide therefore gives a module of one foot and columns two feet thick and fourteen feet high.

For the eustyle temple of Book III the module is the whole diameter. The front is divided into 11½ parts for four columns, 18 for six and 24½ for eight, and one part is the thickness of a column (III.3.7). For the Tuscan temple he works from the width of the building instead: the column is a third of the width high, and its thickness a seventh of its height (IV.7.2). A reader of Vitruvius has to check, passage by passage, which unit is meant.

℟The Doric module

Divide the front of a Doric temple into modules; the column’s thickness is two modules, its height with the capital fourteen, the capital one, the architrave one, and the triglyphs one and a half high and one wide.

M = ½ D; column = 14 M; capital = 1 M; architrave = 1 M; triglyph = 1 × 1½ M; metope = 1½ × 1½ M

Vignola: half a diameter, in twelve or eighteen parts

Vignola made the half-diameter the module for all five orders. He divided it into twelve parts for the Tuscan and Doric, and into eighteen for the Ionic, Corinthian and Composite, whose mouldings are finer and need a smaller unit. His column heights are then whole numbers of modules: 14, 16, 18, 20 and 20. His general rule needs no fractions at all, since the pedestal is a third of the column and the entablature a quarter (Vignola’s general rule: 4 : 12 : 3).

℟Column heights in modules

Make the Tuscan column 14 modules high, the Doric 16, the Ionic 18, and the Corinthian and Composite 20, the module being half the lower diameter.

Tuscan 7 D · Doric 8 D · Ionic 9 D · Corinthian 10 D · Composite 10 D

Palladio: sixty minutes

Palladio divides the lower diameter into sixty minutes and uses the whole diameter as his module, except in the Doric, where he takes half the diameter, divided into thirty minutes, because it suits the divisions of that order (Book I, ch. 13). The minute is therefore the same length in every order, one sixtieth of D; only the module changes its name.

The English handbooks: the whole diameter

The English handbooks of the eighteenth century were written for builders as much as for architects, and they avoid modules and parts where they can. James Gibbs’s Rules for Drawing (1732) works by division: the given height is cut into equal parts with the compasses, one for the entablature and four for the column when there is no pedestal, and each part is divided again, so that the diameter is found from the height rather than the height from the diameter (Divide, do not multiply). Isaac Ware, whose Complete Body of Architecture appeared in 1756, also gives his proportions in diameters. The diameter has remained the usual unit in English books since.

Converting between them

To turn modules of half a diameter into diameters, halve them. To turn Vignola’s parts into diameters, divide by 24 in the Tuscan and Doric and by 36 in the other three orders. To turn Palladio’s minutes into diameters, divide by 60. Vignola’s Corinthian capital, given as 2 modules and 6 parts, is therefore 2⅓ modules, 7⁄6 D, or 70 minutes.

A worked example

Suppose a Corinthian order with pedestals is to be set out after Vignola under a cornice 9.5 metres above the ground. Divide 9.5 m into nineteen parts of 0.5 m. The pedestal takes four (2.0 m), the column twelve (6.0 m) and the entablature three (1.5 m). The Corinthian column is twenty modules, so the module is 6.0 ÷ 20 = 0.3 m and the lower diameter 0.6 m. One of Vignola’s eighteen parts is then 16⅔ mm. The other members follow:

• Capital: 2 modules 6 parts = 0.7 m = 7⁄6 D = 70 minutes.
• Architrave: 1½ modules = 0.45 m = ¾ D = 45 minutes.
• Frieze: 1½ modules = 0.45 m = ¾ D = 45 minutes.
• Cornice: 2 modules = 0.6 m = 1 D = 60 minutes.
• Pedestal: 6⅔ modules = 2.0 m = 3⅓ D = 200 minutes.

Now set out a column of the same 0.6 m diameter after Palladio. His Corinthian is 9½ D, so the column is 5.7 m high, 0.3 m shorter than Vignola’s, and his entablature, a fifth of the column, is 1.14 m, or 114 minutes, against Vignola’s 1.5 m. The same diameter gives a different order according to whose rules are followed, which is why a dimension in modules means little unless the author is named with it.