University of Virginia Library

I.14.4

THE SCALE OF THE PLAN
AND ITS RELATION TO THE
CAROLINGIAN FOOT

Having established that the Plan was drawn to a consistent
scale we must then ask whether this scale was invented for
this specific purpose, or whether it was related to any
regular Carolingian system of measurement. I believe that
the original scheme of the Plan of St. Gall was drawn with a
regular Carolingian straightedge, 40 Carolingian inches
long, and that the designer of the scheme established the
overall dimensions of the monastery site by assigning to it
a length of 40 and a width of 30 Carolingian inches.

The modern English foot is the equivalent of 30.48 cm.
The classical Roman foot was 29.60 cm. The Carolingian
foot was larger and, despite Charlemagne's attempt to
standardize weights and measures, appears to have been
afflicted by a good deal of regional variation. Kutsch,
Schmidt, and Behn in measuring Carolingian churches
believed that they were able to establish its length as 34.00
cm.; Hanftmann and Arens as 33.29 cm.; Rave as 33.3033.50
cm.; and Doppelfeld as 30.04 cm.[367] The studies of
Felix Kreusch[368] and Leo Hugot[369] suggest that the Palace
Chapel at Aachen was built on a Carolingian foot whose
length corresponded to 33.30 cm. This is the exact equivalent
of the old Drusian foot, which the agrimensor Hyginus
tells us was in use in the territory of the Tungri[370] and which
Drusus adopted from the Belgians as a northern standard
for the border settlements of the Agri Decumates. This foot,
two digits longer than the Roman foot, appears to have
been the traditional standard measure of the Franks and
may have formed the base of the commonest building foot
used in medieval France and England.[371]

[ILLUSTRATION]

67. PLAN OF ST. GALL

No other drawing shows the unique conceptual elegance
of modular design to any higher degree of purity and
perfection: the dimensioning of the two intersecting spatial
volumes of nave and transept as multiples of a 40-foot
square, and determination of the width of the aisle in
an ingenious division of the 40-foot measure (16 modules of
2½ feet) as is shown in figure 67.

Possibly, in a preliminary draft of the Plan, the aisle
had been taken by the designer as one half of the nave width.
This could account for the inscription PEDUM XX (see caption
for figure 68). Further consideration, probably of a
pragmatic nature, resulted in the aisle width adopted,
3 + 3 + 3 units—3 modules for the width of the aisle
altars and 3 modules clearance space on each side of each
altar. This method of division gave a splendid trinity of
threes, with 7 modules left over, all in admirable conformity
with St. Augustine's admonition on number (page 118).

This illustrates well how a scheme of modularity can be
selectively manipulated to yield relationships of some
complexity, variety and interest, quite removed from unmitigated
repetition of the same measure, inherent in a grid of
equal divisions. The grid can be banal, but it need not be.

Imaginative manipulation of the sacred number dogma as
seen here, while not exactly typical practice, besides
revealing cognition of alternatives to monometric
schematism, responds to exigencies of a situation. Theology,
liturgy, convenience, amenity, and structure, needed to be
resolved in an effective layout, and were.

Figure 67 notes the concept as it existed in the author's mind
before modifications that would have to be made in places
where a purely intellectual concept—easy to express in a
simple line drawing—came into conflict with progmatic
realities such as allowances for wall thickness. Such conflict
was inevitable where two buildings shared a common wall
in which case the space needed for masonry would have
to be subtracted from the interior of these buildings rather
than from the open areas around them.

STEP 1: CONSTRUCTION OF THE LAYOUT OF THE MONASTERY CHURCH

The foot used in the Plan of St. Gall, if calculated on its
present dimensions, amounted to 32.16 cm. However,
attention must be drawn to the fact that the parchment on
which the Plan is drawn was subject to a considerable
amount of shrinkage. Even today, as Dr. Duft has observed,
when displaying the Plan in its showcase, the surface of the
parchment expands and contracts in response to the
changing humidity content of the air. Konrad Hecht, who
has made some interesting observations on this subject[372]
estimates the mean loss by shrinkage to which the Plan was
exposed through the ages to be 5 to 6 percent. If we modify
the figure obtained from the present shrunken surface of
the Plan by this quotient, the metric equivalent of the
Carolingian foot which was used in the Plan is more likely
to have been around 34.00 cm., which would conform to
the findings of Kutsch, Schmidt, and Behn. It could
equally well have been the exact equivalent of the old
Drusian foot of 33.30 cm., which appears to have been the
historical prototype of the Carolingian foot.

Tabulated in their respective order of magnitude, the
relation of the graduations shown on the straightedge used
in designing the Plan to the actual dimensions for which
they stood are as follows:

• 1. Dimensions of the entire monastery site:

  30 × 40 Carolingian inches = 480 × 640 feet.

• 2. Super module:

  10 × 10 Carolingian inches = 160 × 160 feet.

• 3. Large module:

  2½ × 2½ Carolingian inches = 40 × 40 feet.

• 4. Standard module:

  one sixteenth of 2½ Carolingian inches (i.e., one
  sixteenth of 40 feet) = 2½ feet.

• 5. Submodule:

  one thirty-second of 2½ Carolingian inches
  = 1¼ feet.

It should be noted that the value of the crossing square
(2½ Carolingian inches square) is developed from the value
of the next largest module (10 Carolingian inches square)
in the same manner in which the value of the small unit
(one sixteenth of 2½ Carolingian inches) is developed from
the crossing square: by the method of binary section.

All the surface calculations of the scheme are determined,
accordingly, by a geometrical ground relationship in which
each smaller base value is calculated as one sixteenth of the
superordinate value: the large module (40 feet square) is
one sixteenth of the super module (160 feet square), the
small module (2½ feet square) one sixteenth of the large
module (40 feet square).

In handling these modules, the designing architect displayed
an extraordinary sense of discretion, using each for
its specific purpose: the super module (160 feet square) for
the calculation of the overall relationship of the site, the
location of the axis of the Church, and the grouping of the
principal building masses (fig. 63); the large module (40

feet square) for the square schematism of the Church and
Claustrum (fig. 61); the small module for all dimensions
that were too small to be expressed by any of the larger
modules (figs. 59 and 60).

The Plan is drawn to a scale in which one foot on the
ground corresponds to one sixteenth of a Carolingian inch
on the parchment (which corresponds roughly to the
metric scale of 1:200), a ratio that one would consider even
today ideal for a plan of this kind, as it allows for easy
readability of details without obscuring primary values.

Figure 66A-D shows all of these relationships coordi-

nated on a straightedge that would correspond to one-fortieth
of the yardstick of 40 Carolingian linear inches,
which we presume the drafter of the Plan used in designing
the scheme. See also Diagrams I, II, pages 92 and 93, above.