University of Virginia Library

I. 12

METHOD OF RENDERING

I.12.1

USE OF DIFFERENT COLORS FOR
DRAWING AND EXPLANATORY TITLES

All linear work on the Plan is rendered in a clear vermilion
ink which has retained its original intensity. The lines are
traced without the aid of instruments, in firm and fluent
strokes suggesting that the draftsman had experience with
this type of drawing. The textual annotations are written in
a deep-brown ink, bordering on black. In the crossing,
transept, and forechoir of the Church, brown ink is also
used to thicken the architectural line (fig. 99), obviously
with the intent of clarifying the basic spatial divisions of
the Church, which are somewhat blurred in this area by the
heavy concentration of stairs, altars, benches, and choir
screens.[241] It is impossible to say whether this was done at
the time the Plan was copied, or at a later stage, preparatory
to its use in actual construction.

The Plan of St. Gall is not the only Carolingian manuscript
where a vermilion red is used for the delineation of
buildings. The Zentralbibliothek in Zurich has among its
holdings an early ninth-century copy of Adamnan's book
De locis sanctis,[242] written in the scriptorium of the monastery

[ILLUSTRATION]

42. THE CHURCH OF MOUNT SION

ZURICH, Zentralbibliothek

Codex Rhenaugensis LXXIII, fol. 9v

[courtesy of the Zentralbibliothek, Zurich]

of Reichenau (Cod. Rhenaug. LXXIII), which displays the
plans of a group of Early Christian pilgrimage churches of
the Holy Land drawn, it seems, by the hand of Walahfrid
Strabo,[244] viz., on fol. 5r, the Holy Sepulcher Church of
Jerusalem (fig. 41); on fol. 9v, the Church of Mount Sion
(fig. 42); on fol. 12r, the Ascension Church on Mount
Olive (fig. 43); and on fol. 18v, the cruciform church of
Samaria (fig. 44). As on the Plan of St. Gall, so here, the
architectural plans are drawn in red, while the explanatory
titles are written in black. This suggests that red might
have been the preferred color for architectural drawings in
the early Middle Ages.

I.12.2

COMBINATION OF VERTICAL AND
HORIZONTAL PROJECTION

All buildings and installations shown on the Plan are
rendered in vertical line projection. In certain instances,
however, to this projection is added a straight-on view,
showing the elevation of a wall as though it were lying flat
on the ground. Examples of this are: the arcaded walls of
the cloister walks (Monks' Cloister [fig. 191], Novitiate and
Infirmary [fig. 236]), the arcuated porches of the Abbot's
House (fig. 251), and details such as the crosses on the
altars of the Church (fig. 251), or the monumental cross in
the graveyard (fig. 430). In tracing these elements the
architect made use of the mason's age-old habit of sketching
architectural elevations on the ground when explaining the
design of a building to an apprentice or a client. The method
was even more familiar to carpenters, who not only laid out
but actually cut, assembled, and jointed many of their roof-supporting
trusses on the ground before raising them into
the vertical plane with pulley and ropes.

The designer of the scheme of the Plan employed this
device with discretion—only in places that offered sufficient
space to use it without obstructing other architectural
features or blurring the general clarity of the Plan. In this
manner he succeeded in conveying to the builder, in unmistakable
language, not only the design but also the exact
proportions of the great galleried porches that surrounded
the cloister yards and served as connecting links between
the claustral buildings.

The combination of vertical and horizontal projection in
one and the same architectural drawing or plan probably is
a principle as old as architecture itself and common to all
periods. It was firmly established in Egyptian art and was
there refined to a point where it depicted not only the
planimetrical layout of the buildings with which it was
concerned, but also the human events that took place in
these settings. This led to compositions of great complexity,
in which features drawn in elevation (favored because of
their ability to tell a story more fully and more conspicuously)
tended to overcrowd and blur the plan.[245] The house
shown in figure 45.A-B is a simple and easily readable
example of this tradition. Others are not so susceptible to
easy interpretation.[246]

It is not so widely known that an admixture of vertical
and horizontal projection is also found in Roman architectural
drawings, although there it is not used with comparable

[ILLUSTRATION]

43. CHURCH OF
THE ASCENSION ON MOUNT OLIVE

ZURICH. Zentralbibliothek. Codex Rhenaugensis LXXIII, fol. 9r

[courtesy of the Zentralbibliothek, Zurich]

[ILLUSTRATION]

44. CRUCIFORM CHURCH OF SAMARIA (ISRAEL)

ZURICH. Zentralbibliothek. Codex Rhenaugensis LXXIII, fol. 18v

[courtesy of the Zentralbibliothek, Zurich]

profusion. This can be inferred from the famous
Forma urbis, the now-fragmentary plan of Rome that was
incised in marble during the reign of Emperor Septimius
Severus, between A.D. 205 and 208.[247] Generally rendered in
vertical projection (typical examples are shown in fig. 46),
this plan shows arcuated elements incised in elevation in at
least three different places, each time in connection with the
representation of an aqueduct (fig. 47.A-C).[248] As on the Plan
of St. Gall this delineation of arch forms occurs only in
relatively uncluttered areas of the Forma urbis; in more
crowded sections a more compact symbol of piers, or bars
connected by two curved lines, is used (fig. 47.D-F) for
aqueducts as well as other types of arches.

I.12.3

LACK OF DEFINITION OF WALL
THICKNESS

The walls of the buildings of the Plan of St. Gall are
rendered as simple lines. This fact has given rise to two
widely held assertions of questionable validity. One of
these, voiced as early as 1848[249] and frequently reiterated, is
that the designing architect failed to give any consideration
to wall thickness. The other, more recently advanced, is
that any preoccupation with wall thickness would have been
intrinsically incompatible with the ideal character of the
Plan.[250] As far as the first of these two contentions is concerned,
attention must be drawn to the fact (generally overlooked
in previous discussions of this point) that there are
two significant exceptions: the bases of the columns in the
nave of the church and the foundations of the arcade piers
in the western paradise are rendered as squares, in their full
planimetrical extension. Second, although the draftsman
drew his walls in simple lines, there is clear indication that
he was fully aware of the complications that might arise in
the actual erection of buildings drawn in linear projection
in such areas of the site where the masonry in two adjacent
structures would congest the available building space, unless
special provisions were made to forestall that eventuality.
The fact that the aisles of the Church are 22½ feet
wide and not 20 feet, as their titles prescribe, finds its
explanation, as will be shown later on, in the draftsman's
awareness of this danger.[251] Yet even here he does not go so
far as to draw the walls with two parallel lines, but guards
himself against cluttering his plan with unnecessary details
by simply moving his wall lines farther outward and thus
introducing a safety margin of 2½ feet on either side of the
Church. His decision to render the walls of the buildings by
single rather than double lines has little to do with the ideal
or paradigmatic nature of his subject, but is clearly conditioned
by the small scale of the Plan. Even today, as Konrad
Hecht has pointed out correctly, an architect faced with the
design of a project of similar complexity, drawn at a comparable
scale, would invariably choose the same method.[252] It was for this very reason that the architects who designed
the monumental marble plan of the city of Rome chose

[ILLUSTRATION]

46.A.B.C. FORMA URBIS ROMAE

ROME, ANTIQUARIUM COMMUNALE DEL CELIO

[after Carettoni, Colini, Cozza, and Gatti, Rome, 1960]

These fragments are of a plan of the city of Rome, etched in marble during the reign of Emperor Septimius Severus, between A.D. 205 and 208.
This plan, incised on numerous marble slabs, was installed near the Forum of Peace, on the wall of a building which before the fire of 192
served as municipal archives. A probable outgrowth of the emperor's fiscal reform, the plan may have served as a monumental compilation and
permanent record of numerous archival and boundary maps. Mounted on a base 4 meters high, the plan itself covered a surface about 42½ feet
(13m) by about 59 feet (18m), an impressive area of ca. 2,500 square feet (234 sq. m). It was drawn at a scale of 1:240, occasionally varying
to 1:245.

The walls of the overwhelming majority of buildings are drawn in single-line projection. A typical example of this method is shown in A, a
marble fragment showing the plan of the Horrea Lolliana and adjacent structures (fragment 25; Carettoni, pl. XXV). Exceptions to the rule are
found in the rendering of the plans of temples, where the cellar walls are indicated by parallel lines, as is shown in fragments 31bb and 37a,
delineating the temples of Argentina and Juno (IBID., pls. XXIX and XXXII, respectively).

single-line definition as their standard mode for rendering
walls.[253] When the Romans were faced with the task of
drawing the plan of an individual building, at a larger scale,
they defined the walls in thickness by two parallel lines, as
was done on the marble slab of Claudia Octavia, now in the
Museum of Perugia (fig. 48), and on a number of other
Roman fragments displaying house plans.[254]

This mode of rendering is of great antiquity and we can
safely assume that it was used at all times in all civilizations.
It existed in Egypt at the side of the more pictorial representations
of the type exemplified by figure 45.A, as is clearly
displayed by the detail of a house plan of the New Kingdom
shown in figure 49. Indeed the most accomplished plans
of this kind, as Ludwig Borchard has pointed out, were
probably those which Egyptian architects chiseled in full
size into the pavement of sacred sites, to be used as guidelines
for the masons who built the walls of the temples that
rose in these places.[255] The designers of the Forma urbis
were not entirely consistent in their use of the single line,
but interspersed it with a small number of buildings where
walls are defined by parallel lines. This was done, it seems
without exception, in the rendering of temples (here
exemplified in figures 46.B-C)[256] and it looks very much as
though this departure from the regular method may have
been motivated by the desire to throw into visual prominence
buildings of a strictly religious nature. The designer
of the Plan of St. Gall could have introduced a similar variation—the
church plans in the Cod. Rhenaug. LXXIII
(figs. 41-44) show clearly enough that the definition of
wall thickness by means of parallel lines is fully within the
range of working patterns of a Carolingian architect. If he
chose to stay away from this type of rendering, he did so
predominantly for stylistic reasons, viz., the desire for
homogeneity of design and, above all, an unwillingness to
clutter up his plan with parallel lines that could be confused
with benches, or run parallel to benches, as they would have
done practically everywhere along the walls of the Church.

I.12.4

DIFFERENTIATION OF LEVELS IN
DOUBLE-STORIED STRUCTURES

Whether a building on the Plan is a single- or a double-storied
structure cannot be inferred from its linear layout.
Structures of several stories are designated as such by their
explanatory titles. One must infer from this that other
buildings, which are without such explanations, are one-storied.
The multi-level buildings are: the Dormitory (fig.
208), the Refectory (fig. 211), and the Cellar (fig. 225), the
Abbot's House (fig. 251), the choir and crypt of the Church,
the Sacristy and the Vestry, the Scriptorium and the
Library (fig. 99). In projecting the design of these buildings
onto his parchment, the draftsman is not consistent, but
switches from the rendering of the ground floor to that of
the second story, whichever is of greater interest to him.
Thus, he depicts the layout of the Refectory with its tables
and benches in full detail and merely indicates with the
inscription supra uestiarium that the Refectory is surmounted
by an upper level serving as storage for the
monks' clothing (fig. 211). In the case of the Dormitory
(fig. 208) he follows the opposite procedure. He depicts the
layout of the upper story with the beds of the monks and
explains with the inscription subtus calefactoria dom' that the
building has a lower level, which is occupied by the warming
room of the monks. Conversely, in the case of the Cellar
(fig. 225), he dwells with loving care on the two impressive
rows of wine and beer barrels set up on the ground floor,
and suggests by the legend supra lardariū. &' necessariorū
repositio that the Cellar is surmounted by the Larder. In
only one case, namely that of the choir and the crypt, are
elements of two levels combined on the same surface. The
area is of crucial importance from a liturgical point of view,
and the draftsman uses this device to make absolutely sure
that it is clearly understood in what manner the pilgrims
are given access to the tomb of St. Gall.

The designers of the Forma urbis Romae also seem to
have felt free to switch from the predominantly ground-floor
layout method to an ideographic rendering of the
superstructure, when this was a more interesting and
significant aspect. Buildings such as the Colosseum (fig.
50.A) or the Theater of Marcellus (fig. 51.A) are rendered in
bird's-eye view, or in a combination of bird's-eye view and
planimetrical projection. Thus in the Colosseum a sequence
of elliptical lines defines the four major sections of the
theater, corresponding to the podium and the three maenia
for the spectators, suggesting rows, yet not specifically
representing them in their actual number.[257] In the representation
of the Theater of Marcellus (fig. 51), in addition
to the semicircular tiers of seats and the passage ways
(praecinctiones) by which these are separated, there is a
complex system of fan-shaped passages that intersect the
seats radially. Some of these represent the ascending stairs
in the superstructure that connect the three tiers (cavea) of
seats (and would have been visible to anyone seated in the
theater); others show the hidden ramps (cryptae) in the substructure
(not visible from above) that give access to the
upper deck through openings (called vomitoria, because
they "spit out" the masses of spectators into the galleries).
This is an ideogrammatic contraction on one and the same
plane of elements belonging to different levels and not
visible simultaneously from the same point of inspection.
A comparison of the portrayal of these two buildings on the

[ILLUSTRATION]

47.A,B,C,D,E,F FORMA URBIS ROMAE, FRAGMENTS

ROME, ANTIQUARIUM COMMUNALE DEL CELIO

[after Carettoni et al., 1960, vol. II]

A. Fragment 517. Four arches of an aqueduct shown in elevation (Carettoni, pl. LII).

B. Fragment 223. Five arches of an aqueduct shown in elevation, perhaps the Aqua Alsietina (IBID., pl. XLII).

C. Fragment 612. Sequence of arches of an aqueduct shown in elevation, changing direction at an obtuse angle (IBID., pl. LVI).

D. Fragment 215. Series of arches of an aqueduct, with arches shown in vertical projection by curved lines connecting with piers (IBID., pl. XLI).

E. Fragment 413. Aqueduct arches shown in vertical projection by curved lines connecting with crossbars (IBID., pl. XLVIII).

F. Fragment 480. Aqueduct with arches shown in vertical projection by curved lines connecting with crossbars (IBID., pl. L).

* position of fragment not identified

Forma urbis with modern architectural drawings of the same
subjects (figs. 50.B and 51.B) shows in the rendering of these
details how little they conform to a consistent scale or to
dimensional accuracy—and how difficult it is (especially
in the case of the Marcellus Theater) to determine what
belongs to the upper deck and what to the supporting
structure. To render the relationship of all these elements
in accurate planimetrical projection would have necessitated
making as many separate plans as there are different stories
in each building (or a combination thereof as is done in
figs. 50.B and 51.B), which was clearly beyond the scope and
function of the Forma urbis. In his rendering of the Colosseum
the designing architect confined himself to portraying
in a crudely abbreviated form what a spectator
would have seen of the elliptical seating arrangement of this
amphitheater, had he hovered vertically above it. In his
portrayal of the Theater of Marcellus, by contrast, he made
an attempt to combine distinctive features of the substructure
(not visible from above) with distinctive features
of the upper deck (visible from above) without making it
clear what belongs to one, what to the other.

The conception of the Plan of St. Gall is highly superior
in this respect. In his layout of the transept and the presbytery
of the Church (fig. 99), where the component parts of
several levels are shown in simultaneous projection, the
author defines the interrelationships so clearly that the eye
finds no trouble in establishing that the presbytery is
raised above the level of the transept by seven steps and
that the vaulted arms of the ambulatory corridor crypt lie
beneath that level. He makes it unequivocally clear that the
longitudinal arms of that crypt run along the outer surface
of the choir walls and terminate in a transverse arm that
gives access to the tomb of St. Gall. He leaves no doubt
about the length and width of these arms.

With all of this I do not mean to imply that a Roman
architect might not have been equally proficient. To place
this entire problem into proper historical perspective the
reader must here be reminded of the fact that the Forma
urbis was not only drawn at a considerably smaller scale
(1:240) than the Plan of St. Gall (1:192), but also that it
included buildings of exasperating constructional complexity
and most important of all, that it was never meant
to serve as a building plan to be used in construction; it
was more in the nature of a real estate record. Considering
its scale and its purpose, it renders with admirable conceptual
simplicity the layout of such complex structures as
the Colosseum and the Theater of Marcellus.[258]

I.12.5

LACK OF SPECIFIC INFORMATION
CONCERNING BUILDING MATERIALS

The Plan does not give explicit instructions for the materials
with which the individual buildings were to be constructed.
All installations are rendered in a uniform line,
and this line may stand for a masonry wall, a wooden fence,
the outlines of a bench or a table, or a seedling bed in the
vegetable garden. It is fairly obvious, however, both in
view of the peculiarity of their design and the prevailing
building customs, that stone construction was envisaged
for the nuclear claustral structures: the Church, with its
columnar order, its circular towers, and apses; the Cloister,
with its round-arched galleries and portals, as well as the
monastic buildings directly contingent to the Cloister; the
Dormitory, the Refectory, and the Cellar. To these should
be added the complex that contains the Novitiate and the
Infirmary with its round-arched cloister walks and round-apsed
chapels, and, finally, the Abbot's House with its
arcuated porches. Whether masonry can be postulated for
any of the remaining structures is a controversial question
to which special attention will have to be given later in this
study.[259]

I.12.6

DIFFERENTIAL ATTENTION IN THE
RENDERING OF DOORS

An interesting case of discrimination between buildings of
lesser and greater importance can be observed in the
rendering of the doors. Throughout the whole expanse of
the Plan the location of a door is designated by two short
strokes intersecting the walls at right angles. In buildings
of major importance, the wall line stops as it reaches the
first crossbar and takes a fresh start in the center of the
opposite bar

. In buildings that hold a
lesser rank in the religious or social hierarchy of the
monastery the wall runs through as a continuous line, and
the crossbars simply intersect it

[ILLUSTRATION]

. This is,
of course, a faster way of rendering, which the draftsman
first substituted sporadically for the more exacting manner
as his hand got tired in the tracing of individual structures,
and then consistently as he turned from the primary to the
secondary buildings. In the Church (fig. 55), the most
important building of the Plan and the first to be traced,
there is only one instance of the abbreviated form: one of
the passages in the barrier that connects the penultimate
freestanding pair of columns, significantly enough, in a
place where the line straddles the seam of two connecting
sheets of parchment. In the atrium west of the Church there
are two more cases: the two openings in the wall that connect
with the passages of the two towers. There is none in
the Abbot's House (fig. 251), nor the Outer School (fig.
407), and only one in the House for Distinguished Guests
(fig. 396), one of the entrances to the stables of the horses.

[ILLUSTRATION]

48. MARBLE SLAB OF CLAUDIA OCTAVIA

PERUGIA, MUSEO ARCHEOLOGICO NATIONALE DELL' UMBRIA

[courtesy Soprintendenza alle Antichǐtà dell' Umbria]

The slab displays the plan of a sepulchral monument (large building, right), and the house of its guardian (smaller building, left). The third
plan (in center, and at top) shows the basement of the guardian's house. Walls are rendered by two parallel lines; doors are indicated by
continuation of the outer line or by interruption or bending of both wall lines. Stairs are indicated varyingly as a sequence of parallel lines or as
two converging lines. The dimensions of the room are designated by Roman numerals. Gatti, who analyzed the plans, came to the conclusion
that they were drawn in three different scales: that of the sepulchral monument at the scale of 1:84; those of the guardian's house at the scales
of 1:140 and 1:230, respectively (see Carettoni ET AL, 1960, I, 210).

The incidents increase as the draftsman works himself
through the claustral structures, and thereafter the abbreviated
method of rendering becomes routine. The first
building drawn entirely in this style is the Hospice for
Pilgrims and Paupers (fig. 392). In some of the more
important guest and service buildings, such as the Great
Collective Workshop (fig. 419), and the House for Horses
and Oxen and Their Keepers (fig. 474), the two methods
are judiciously combined: the disrupted line for the principal
entrances, the undisrupted line for the secondary
doors. In the buildings to the east of the Church the continuous
line is standard; the disrupted line, the exception.
And in all of the buildings that lie to the west of the Church,
there is only one occurrence—obviously accidental—of the
disrupted line, in the House for Sheep and Shepherds and
Their Keepers.

I.12.7

THE PLAN IN HISTORICAL
PERSPECTIVE

The method of rendering used in the Plan of St. Gall is
closely related to that displayed in the great marble plan
of the city of Rome made under Emperor Septimius
Severus, and belongs to the same historical tradition of
rendering. Functionally, these two plans have little in
common. The Forma urbis delineates an existing condition,
the layout of a grown city. The Plan of St. Gall does not
define how it is, but how it should be. These differences,
however, had little, if any, effect on the manner in which
the two plans were rendered.

Like the architects who designed the Forma urbis, where
wall thicknesses are indicated in a few judiciously selected
categories of building, the author of the Plan of St. Gall
would have been fully capable of rendering the walls of his
buildings in full thickness. Like the former, he chose not
to employ this method for the same reason an architect
today would use single line projection instead of double line
projection for the rendering of walls, namely, the complexity
of his subject and the smallness of the scale in which
it was drawn. There is good evidence that the Forma urbis
was still in place on the walls of SS. Cosmas and Damian
in the Carolingian period,[260] and thus could have been seen
by the Frankish emperors who visited Rome and the
architects who traveled in their following. Moreover, there
are more substantive reasons for thinking that the designer
of the Plan of St. Gall was familiar with the layout of the
city of Rome.[261]

If it was the purpose of the Plan of St. Gall to depict on
a single spread of parchment the layout of the buildings and
furnishings of a paradigmatic medieval monastery, it would
be hard to improve upon the method of rendering that the
designer chose in order to accomplish this task. One of the
most successful features is the freeness and flexibility of
mind with which the designer switches from the rendering
of the ground floor to the rendering of an upper level—

wherever the complexity of the layout of the upper floor
suggested such action—and chooses to explain the nature
and function of the repressed story with the aid of an
explanatory title. To do it differently would have required
supplementary drawings. Even from a purely technical
point of view the Plan of St. Gall is a highly sophisticated
document. It tells the story of a very complex architectural
situation with ingenious simplicity. One of the designer's
overriding preoccupations was the retention of clarity in
the over-all appearance of the settlement. He was detailed
where attention to detail was imperative in the light of
function; but he did not hesitate to omit almost entirely
such features as stairs where their delineation would have
impaired the clarity and easy readability of the primary
elements of his drawing.

With all its medieval idiosyncraises, the Plan of St. Gall
has a surprisingly modern flavor. Its analytical precision
and clarity compare favorably with any modern site plan
drawn at a comparable scale. The designer did not hesitate
to enliven his plan with elevations in a few places, where
this method promised to convey his thoughts more fully;
but in departing in this manner from his general mode of
rendering he proceeded with a deep sense of discrimination
and with conspicuous self-restraint. Above all he carefully
resisted any temptation to indulge in architectural pictorialism.
This quality is strikingly revealed if one compares
the Plan of St. Gall with the twelfth-century plan of the
Waterworks of Christchurch Monastery at Canterbury
(fig. 52) where everything is shown in elevation as in a
child's drawing.

[ILLUSTRATION]

50.B FLAVIAN AMPHITHEATRE (COLOSSEUM)
PLAN

ROME, ANTIQUARIUM COMMUNALE DEL CELIO

[after Durm, 1885, 344, fig. 310]

This composite plan of the Colosseum shows four different levels.

[ILLUSTRATION]

50.A FORMA URBIS ROMAE

ROME, ANTIQUARIUM COMMUNALE DEL CELIO

[after Carretoni, 1960, vol. II, pl. XXIX]

These fragments show the seating arrangement of the Colosseum as if
seen from above.

COMMENT:

for figure 50.A and FORMA URBIS ROMAE, generally

The illustration, using the lower portion of the graphic scale graduated 0-100
metres, scales 186 metres on its major axis. This compares with 187.5 metres
(615 feet) commonly given for the length of the Colosseum, a variance of less
than 1 percent between present day measurements and the sculptured mural
version that records the measurements of engineers at a time when the plan
was cut in place in stone.

FORMA URBIS ROMAE stands as a remarkable demonstration of the state of
the art of drawing, with knowledge not only of measure, but the skill of taking
measurements and translating these measurements precisely into a graphic
configuration of great accuracy. Far exceeding any practical function, such as
a cadastral plan for administrative purposes, must have been its effect on the
mind of the beholder. The impact on a viewer of the plan of Rome, incised in
stone for all time, spread across a wall 59 feet wide and rising, on its base,
to 56 feet, could not but impress even the most sophisticated Roman. For the
visitor from beyond the hills of Rome and from lands afar, the effect could
not have been less than overwhelming.

The conjecture is tempting, that the sculptural mural map may have been
seen, if not by the great Carolus himself, by learned men of his court and
soldiers of his entourage in the course of their duties in Rome.

A record of achievement, symbol of law and order and authority, invincible
and eternal, it seemed without doubt, and a fitting inspiration as well, for an
emperor and his sometimes loyal and always ambitious followers.

The comparative scale, included with the illustration, compares the scale of the
sculptured plan above, the line (40 cm), with the actual "on the ground"
measure (100 m), below. The ratio, 41.7 cm. to 100 m, is almost 1:240.
The ratio between the scale of illustration 50.A and the Colosseum computes
at about 1:951.7 (derived from the relation between 19.7 cm = 187.5 m).
Thus the illustration is about ¼ the size of the rendering of the plan on the
sculptured wall.

1/952/1/240 = 240/952 = 1/3.98 [or ¼]