Visual
thinking, alliance between painting and architecture, design history and
psychology of architectural invention, interdependence of building and urban
scales are at the heart of Eduard Sekler's œuvre. They are also
leitmotifs in the present essay, a small token of appreciation for his great
contribution.
The
case at hand is the conception of the angular bastion, an important
revolutionary event, about which one cannot but agree with J. R. Hale (1965)
that it was the most original of all architectural forms invented in the
Renaissance. Vasari wrote about it in Le Vite, crediting Michele
Sanmicheli with having introduced it in his project for the Cornaro and S.
Croce sections of the fortification in Padua. As opposed to the round
configuration, Vasari remarks, the angular configuration of the bastion is
efficient as well as effective. Most historians since, agreeing with Vasari's
attribution to Michele or not, have continued to discuss the development of
fortifications in the same terms, as a transition from the round to the angular
bastion, limiting their search to the problem of who conceived it first and
when. Fewer historians have tried to justify Hale's claim and explain the
significance of this invention. Even fewer have tried to explain how this new
important conception came about, and those who have usually invoked
technological reasons, in particular the appearance of the cannon, for the
emergence of he angular bastion.
This
paper differs from most previous studies in its focus on the cognitive factors
which contributed to the creation of the angular bastion. Shifting our
attention away from military "hardware" has two results. It shows
that the significance of the emergence of the modern bastion lies not in the
new looks of the product so much as in the 'evolutionary aspects of the very
design thinking that brought it about and the new programmatic imperative motivating
the thinking mechanism.
Our
investigation will demonstrate the function of image representation, and the
use of precedent and analogy in creative design. We will look at how cognitive
factors, hat is to say design thinking "software" -the conventions
through which the problem If fortification was represented -, rather than
military "hardware", contributed in the creation of the angular
bastion and what the catalytic function of image representation, is in the use
of precedents and analogy in creative design. We will finally suggest that this
new fortification design had repercussions in architecture and urbanism which
go well beyond the world of defense.
In
order to study the angular bastion as design invention, as a cognitive
phenomenon, we have to turn to the documents, to the drawing and texts employed
in solving fortification design problems rather than to the material reality of
the bastions themselves.
The
first discussion of the angular bastion goes back to Vitruvius. His De
Architectura contains a passage (Bk I. Ch. V) devoted to the fortifications
of cities which will serve as a point of reference for centuries. Vitruvius
sees fortifications as made out of two basic components, towers (turres) and
walls (muri). He states that towers should be round or polygonal (rotundae
aut polygonae) and not square (quadrata) (Fig. 1). The reasons for
his rejection of the square shape is the fragility of its
sharp angles when attacked by
military
machines (machinae) as opposed to the firmness of the round surfaces (rotundationibus)
under the same circumstances. As for city walls, they can be either round
or polygonal, although he has a marked preference for the round ones for reasons which are no longer are
structural
but related to use. Round walls make the attacker vulnerable, while angles
obstruct the defender and protect the enemy ("anguli pro current,
difficiliter defenditur, quoud angulus magis hostem tuetur quam ivem"). In
addition he believes that the round walls make the enemy visible from several
sides ("Uti hostis ex pluribus locis conspiciatur"), that they have
what we might call a panoptic potential.
From
this sample analysis of the parts of fortification and their good or bad
performance, Vitruvius goes on to discuss the relation between the parts.
Towers have to project outside the line of the wall in order to protect it. The
wall between these projections should not be more than a bowshot long, in case
one of the towers is occupied. This will allow its neighbouring, unoccupied
towers to attack it by means of scorpions and other ballistic engines.
Reversing
the Vitruvian choice, a later Roman author, Vegetius, in his De Re
militarii, prefers angular to circular walls. They are much better at
defending against military engines. Several centuries later, Christine de
Pisan, a poetess, philosopher, champion of the cause of women and theoretician
of fortifications, taking the side of Vegetius in her Le Livre des Faicts d'
Armes et de Chevalerie (written around 1408 [Book II, Ch. XIII]),
recommends "crooked", angular walls.
The
question of circular versus angular bastions is dealt with once more in a
treatise written forty years after Christine de Pisan's, a text which has been
very much underestimated in terms of its contribution to the new military
architecture. This is Alberti's De Re Aedificatoria. It contains three
chapters (Bk. IV Ch. IV, Bk. IV Ch. V, Bk. V Ch. IV) on fortification. These
have been correctly criticised as disregarding the potential of fire arms
(Horst de la Croix 1960, p. 34, J. R. Hale 1965, p. 477). The references to
canons are indeed limited to the mention of "loop-holes almost at the very
bottom of the wall" from "which the enemy is attacked by a weapon".
On the other hand, De Re Aedificatoria has been unfairly criticised (De
la Croix, 1960) as relying too much on classical writers. In fact Alberti
attacks the authors of antiquity who "condemned all Angles for fear of
weakness against military engines and of helping the enemy to hide" (Bk.
IV, Ch. III) and, if he uses traditional Vitruvian concepts, it is in a new
way. The difference is that he no longer sees curved and angular walls and
towers as isolated objects to be examined and evaluated separately, but rather
as hierarchical components of an integrated system, each part related to
another and contributing interactively to an overall objective.1
This means that Alberti combines the Vitruvian imperative of panoptism with
Vegetius' contention that the enemy is repelled more effectively if trapped
between two angles (Bk. IV Ch. 111)2 (Fig. 2). To satisfy both
points of view – the Vitruvian and Vegetian –Alberti proposes a new composite
configuration: he gives to the round Vitruvian fortification an angular
Vegetian outline. The overall fortification is thus inscribed in a convex
shape, while its outline consists of a sequence of embedded concave
"angle" units that Alberti likens to a "Star with Rays running
out to the circumference" (Bk. V. Ch. IV) extending "like the Fingers
of a Man's Hand". Thus, while the global convex shape helps the defendant
survey every point of the region that surrounds him, the local concave parts
force the enemy to be trapped "between two (projected) angles" (Bk. V
Ch. IV).
In
its higher systematic organisation, Alberti's heuristic scheme integrates
fortification elements in a hierarchy of surveillance and defense: "the
wall (is) defended by ...the towers....the towers mutually by one
another," (Bk. IV Ch. IV) and all towers together by "one principal
tower within the fortress built in the stoutest manner, fortified as strongly
as possible, higher than any other part. .." (Bk. V, Ch. IV). Most
innovatively the design is conceived not only as purposeful system but also –
as much as it is possible to analyse it by relying on Hellenistic mathematics –
optimal.3 This means that resources are allocated efficiently to
minimize a negative state while maximizing a positive one. More specifically,
Alberti chooses to inscribe his star-like fortification in a circle because it
offers a pattern which is both "the most capacious of all, and the least
expensive to enclose either with wall or rampart" (Fig. 3).
Alberti uses
words to describe this new system. Design goals and means are explicitly
stated. But the product is hard to visualise. For a visual description of this
new formal pattern we have to turn to Filarete's Trattato (written c.
1460) and to Giuliano da Sangallo's Taccuino Senese, which show a
multi-level hierarchy introducing concentric circles of defence, all
panoptically controlled by a centrally located omnipotent tower. Of course what
is gained in these drawings in terms of concreteness of the description is lost
in expliciteness. The drawings tell us how to shape fortifications but not what
for or why.
Like
Alberti's De Re Aedificatoria, Francesco di Giorgi's summa on
architecture half a century later is a series of small treatises. One of these
is devoted exclusively to military architecture (Fig. 4). The problem of
designing a perfect fortification is seen here a subproblem of the general
category of problems to develop an design system capable of minimising costs (simplicita,
brevissima spesa, piccolo tempo, facilmente applicare) and maximising
benefits (comodita, figura utile, più offesa fortezza, torrone perfettamenta
quadrata).
In other words, it is seen as part of
the search for optimization. The systematic search for optimization
comes out even
more clearly than in Alberti's
writings.4 Di Giorgio cites
extensively, although not always accurately Aristotle's Metaphysics,
Physics, Posterior Analytics and On the Soul. In addition his book
is profusely illustrated, complementing and amplifying rather that simply
commenting on the text. Consistent with what one might call laying bare the
device
of his own thinking, Franceso
devotes part of the text to justifying the use
of drawings and their indespensability in solving the problem of perfect
fortification. The search for the appropriate representation to solve this
problem also comes closer to completion than at any other time before.5
While
up to that moment writings on military architecture had been loosely put
together, Francesco's Quinto Trattato has a carefully articulated
argumentation structure and it even contains an explicit discussion about the
argumentation's own logical organisation (Di Giorgio 1976, p. 414). Stressing
the limitations of abstract contemplation in dealing with complex problems that
lead to an "infinity" of possibilities, Francesco brings in no less
than thirty-eight concrete, extreme cases of alternative solutions,
"examples in design" as Francesco calls them, described through words
as well as through drawings.6
Far from being "doodles," as they have
been occasionally referred to (Hale, 1965), these drawings are instances of
problem solving. They are a series of systematically generated alternatives
carried out with the help not of words or numbers but of figures. And in them,
that is in the visual thinking they represent, Francesco comes close to
designing the angled bastion. Close but not completely. He produces many
solutions but no explicit procedure towards them.
What
kept Francesco di Giorgio from inventing the bastion? What kept his
predecessors from inventing it? The answer might be found in a drawing made by
a famous friend of Francesco's and a great admirer of his writings on
fortifications: Leonardo da Vinci.
Here,
in one of Leonardo's sketches for the fortifications of Piombino (c. 1504), one
observes the outline of a bastion covered by nervous strokes describing
trajectories of cannon balls. These strokes, far from obscuring, enlighten.
They disclose what made possible the invention of the angled bastion and,
indirectly, what kept it from coming about.
We
have already remarked how important Francesco thought visual representation was
as a means of architectural thinking, as a way of grasping phenomena which
otherwise would have remained unrepresented, thus incomprehensible. "Una
lineae e una quantita visible" (Ibid., p. 445) he said. But lines in
Francesco's esempli in disegno only describe built form.7
Leonardo's sketch, on the other hand, maps process, movement, operation in
addition to built form. We see therefore two things represented in the drawing
simultaneously: the outline of the bastion and overlayed upon it, the routes of
missiles hurled from of shooting points. It is a composite representation, the
likes of which are not to be found before. As such, it is a new way dealing
with the fortification problem and a new design solution to the problem.
The
development of this new representation, capable of simultaneously describing
objects moving in space together with objects occupying space and of
superimposing the first onto the second, is a "necessary" condition
for the solution the fortification problem. Through this representation lines
of fire express constraints beyond which the outline of a fortification cannot
expand. Through this device the designer can search systematically now for a
configuration which minimises costs of defense – number of weapons and
defenders and cost of construction – while maximising surveillance. This
method of visual representation makes it easy to "see" that if the
wall deviates from the outline of the trajectories it will result either in
blind spots, undefendable areas, or redundant defence turning the abstract
problem to a concrete procedure. Hence the impression that one has, looking at
the Da Vinci drawing, that the lines of fire running on the side of the walls
actually shape the profile of the fortification. They
"streamline" its outline as James Ackerman (1961) remarked about the
drawings of Michelangelo carried out later for the fortifications for the Prato
d'Ognissanti, or they "scrape" it down, as even later texts refer to
this new concept.
How
did Leonardo think of using this method to design fortifications? How did he
conceive this complex representation system? Where did it come from? Why was it
Leonardo who thought of it?
The
obvious place to search for an answer to these questions is in Leonardo's
drawings more specifically in the analogy between fortification and perspective
drawing (Fig. 5). Just as in a perspective drawing there are visual rays
("razzi luminosi"), so in Leonardo's bastion drawing there are lines
of fire. Just as in a perspective drawing the lineae occultae shoot out
from the eyes, so in Leonardo's sketch lines of fire shoot out from the walls.
Finally, as in a perspective drawing, the lineae occultae help trace the
picture of the object on the paper, so in Leonardo's bastion drawing the lines
of fire form the profile of the bastion.
An
analogy also can be found to hold between the representation system used by
Leonardo to shape fortification walls and the art of representing shadows. As
in fortification design there is a point from which the ballistic lines
originate, and as in perspective the visual lines are drawn from the place of
the eye, so in "sciagraphia" the shadows of objects are projected
from a luminous point. Sciagraphy has a "piramide ombrosa" the way
perspective has a "piramide visiva", which in turn corresponds to the
ballistic triangle defined by the two extreme fine lines in the Da Vinci
drawing.
Through
analogy, the representation system developed for perspective and sciagraphy is
transfered to fortification, mapping familiar problems of vision into
unfamiliar ones of ballistics, connecting objects and relations of explored
domains of art and the terra incognita of the new war. Out of these
connections it is possible to make explicit the constraints that implicitely
underlie the fortification problem and to exploit them in a way that leads to
an optimal solution.
As the
"piramide ombrosa" identifies what is in the dark and what is in the
light, and the "piramide visiva" what is visible and what is
obscured, so the triangle formed by lines of fire indicates what is within the
range of fire arms and what is outside of it, what is defendable and what is
unprotected (Fig. 6). With this new method one is able to plot the outline of
defense polygon which combines a minimum set of lines of fire without leaving
any un- covered points outside the enclosing wall.
The
solution to the optimal fortification problem was possible through the
establishment of an analogy between the knowledge of perspective and sciagraphy
on one hand and fortification design on the other which in turn depended on a
more basic pre-existing analogy between lines of vision and lines of fire at
the heart of the so called "ballistic" model of vision. This analogy
was an old one. Lucretius (ca 55 B.C.) used it when he wrote that objects'
"thrown off bodies" which then enter the eye and Hero of Alexandria
(first century) believed that "just as a stone is violently hurled against
a compact body. ..so the rays (from objects) ...are emitted". Alhazen
(11th century) uses the same kind of analogy in the seventh book of De
aspectibus between light and catapulted "iron balls,"
"thrown swords" or a
"sphere fixed to the tip of an arrow".
Juring
the early Renaissance the malogy becomes widespread and plays an important role
in the development of the science of perspective and "sciagraphy".
The drawing was perceived as resulting from the visual lines shooting from each
point of the objects and: striking the eye after having pierced an imaginary
plane on the way (Fig. 7). As Da Vinci says, echoing Alhazen, "the objects
which are over against the eyes act with the rays like many archers"
(Kubovi, 1986, p. 252) and, to quote Dürer's Unterweysung (1525),
"eind durchsichtiger planus oder eben feld der all streymlinien
durchschneidet" (Ivins, 1938) (Fig. 8).
The
analogy was almost there, but it had to be thought of in a new way, reinvented,
overturned. Rather than lines of vision being seen as lines of fire, lines of
fire had to be seen as lines of vision (Fig. 9, 10, 11). And this was not easy.
That Leonardo was the one to do it and in the process solve the problem of
optimal fortification design is not surprising since he new representation emerged
by analogy to perspective and sciagraphy and he was an expert of both.
The
bastion system invented by Leonardo is clearly illustrated for the first time
in I quattro primi libri di architettura (1554) by Pietro Cataneo. It is
the first book which prints the lines representing lines of cannon fire as
determining the shape of the baluardi, the angular bastions. The first
diagram (p. 11) shows a simple square plan. The side wall (cortina) is
flanked by two walls which form the baluardi which in an angle defend
the cortina by shooting the enemy from two sides. At the same time these two
walls, the faces of the baluardi, are defended by fire shot out
of the two ends of the cortina. As we can easily see, all the parts are now
interlinked functionally, dimension- ally, morphologically, in a hierarchical
pattern of optimal defense. In the new polygonal pattern emerging each point
defends another in a such as manner as to eliminate undefended spots and
redundant defences. In Cataneo's diagram the representation system, is clear
and easy to apply. In addition the diagram is printed and mass reproduced. The
bastion revolution is grounded solidly.
The book by
Cataneo was the last to include both military and civil architecture on equal
terms. Most writings on military architecture that followed leave out the
latter.8
Specialised
military writings contain a multitude of new fortification devices, the tenaille,
ravelins, rondel orman, moyenau, lunette, ouvrage a comes, ouvrage couronne,
contregarde. They also include explicit, detailed step by step procedures
of "how to do it". These patterns and routines make military
architecture increasingly more effective and more efficient keeping up with
improving offensive
weapons and changing general conditions of war. They originate from the angular
bastion not as a form, but as a system of representation and design method.
But
were the new system of representation of the fortification problem and the
bastion born just of the exploitation of pre-existing knowledge? Could
cognitive aspects have ignited the fortification revolution on their own? Or
was it the improvement of fire arms and the growing power of siege artillery
which started the process, a claim which has been stressed since the time of
Diderot's article on fortifications in the Encyclopedie.
Of course the
introduction of the cannon demonstrated that traditional fortifications created
blind spots, undefendable areas. But such troubles had existed before the cannon.
Military architects had
tried
to find ways to eradicate
them. The cannon did not so much pose the problem
as intensify it. We can repeat about the new fortifications what Weber said
about the new systematisation of the army. The cannon was "the result and
not the cause".
Can
one say, then, that the angular bastion, like the systematisation of the army,
as Max Weber claimed, was the result of the march of rationalization and the advance of
bureaucracy,
of the introduction of discipline and mental drilling? After all, there are
many parallels between the two reorganisations. The systematisation of modern
fortifications resembles, from the structural and organisational point of view,
the manner in which the army, soldiers and weapons were arranged within a
systematic goal directed framework. Hierarchical principles had been the
backbone of
Alberti's and di Giorgio's writings on fortification, but also of those of two
major protagonists of the army's organisational revolution, Machiavelli's Arte
della guerra (1552) and Justus Lipsius' half a century later Politicorum
Libri Sex.
However the documentary
evidence
we have does not appear strong enough to support Max Weber's claim. There is no
strong evidence that the systematization of fortifications were associated with
the rationalization of the army beyond a few generalities. The abstract ideals
of bureaucracy, hierarchy, subordination, articulation and order, although they
increasingly dominate the design of fortifications, are not the overriding
norms of the sys- tem. They are themselves subordinated to a higher one,
efficiency.
Efficiency
climbs to the top of the goal system of military architecture only at the time
of Alberti, Francesco and Leonardo. And if we are to associate it to any major
events external to the problem this is the rise of money economy which destroys
old habits of life in peace or war – perhaps it is no accident that while di
Giorgio is finishing his treatise, the Summa de Arithmetica by Luca
Pacioli, containing the first published exposition of double-entry
book-keeping, is being released (1494) – and the mounting cost of war. Being a
soldier becomes a way of making money, a job requiring skill and
specialization, both scarce resources. And as the mercenary soldiers comes to
contemplate his payment with greater interest, his employer in turn becomes
increasingly preoccupied with cost cutting schemes for this new war industry.
The introduction of gunpowder in Renaissance warfare also raises the cost of
war. The cannon introduces new costs, those of its own production, maintainance
and operation. The Ordine del l'Esercito Ducale Sforzesco (Paret, 1986,
p. 15) refers to these costs as disproportionately high in relation to the rest
of war making. The cannon, like any other technological advancement in
fighting, never becomes a cost saving device. In fact it raises the cost of war
and occupies increasingly a more important position in the world economy. And
by the middle of the 16th century the manufacturing of cannons becomes the most
profitable proposition in the iron trade (Cipolla, 1965, p. 40).
Macroscopic
social, economic or political changes, important as they may be, are not
sufficient to make the mind create. They pose new problems but do not help to
solve them. Any act of creation, including design, is the result of a dual
cognitive process. On one hand there is the perception of the emergence of new
imperatives – such as the imperative of economic efficiency – and of new
constraints – such as the new constraints imposed by the technology of the
cannon – which set up new problems and put into motion the search for their
solution. On the other, there is the conception of new representation systems
capable of exploiting these constraints and solving these new problems. And
this was the case with the new representation system derived by analogy from
precedent problems in perspective and sciagraphy which found the solution in
the design of the angular bastion.
As with most human
artifacts, a moment arrives when angle bastions become obsolete. The change in
context within which war is carried out takes its toll. Soon after the end of
the Ancien Regime, angularly bastioned fortifications ceased to be constructed.
In many cases they even started to be demolished, giving way to public
buildings and parks, playgrounds and highways. And those few which did survive
become the object of tourist visits or, often, the hiding place of shelterless
lovers.
This was the dawn of a
new world, where fortifications were no longer needed. Here the money economy
became even more widely spread and deeply rooted than during the Renaissance
and the Ancien regime. The norm of economic efficiency spread across most
aspects of civic life. Control and surveillance became priorities in a large
number of cases of civic architecture, for buildings and urban complexes. Once
more designers were compelled to provide the solution to a new problem. And
once more the rules of intelligent thinking, the "ars inveniendi,"
heuristics, whispered to them: "Have you seen a similar problem? How does
it relate to yours? Can you use precedent solutions? Think by analogy."
The time had come for
the bastion itself to take the role of a precedent to help master the
unfamiliar. And seems it was the bastion and not the Menagerie of Versailles,
the anatomical theater, or the various therapeutic institutions, as has been
claimed, which provided the precedent for the modern workplace, the productive
building and the productive city. But unlike the case of the conception of the
bastion in the Renaissance, where analogical had to transfer knowledge from two
district distant domains, from vision to ballistics, the gap was shorter now.
Innovation
involved transferring structured information between two artifacts
only, the bastion and the
work
place, architectural or urban.
As
in the bastioned complexes, where the military engineers had started from the
analysis of the parts of the fortress, linking each part to the other in a
hierarchical way for the purpose of "continua vigilanzia," of
omnipresent defence control, so in the new workplace, foremen and directors
organised each department of production into networks of increasing inspection
and super- vision, the flow of information between groups playing the same
morphogenetic role the lines of
fire had for fortification. But now the topology of panoptism was
turned inside out. The workplace, the productive building and the city became
objects of a surveillance that was "intramural" rather than extra
muros. And, while the bastion was vanishing as an artifact in the
landscape, it emerged a universal building metaphor on the horizon of the mind.
But this is an altogether different story (Fig. 12).
The
invention of the angle bastion in Italy around 1500 is indeed one of the most
fascinating moments in the history of design thinking and one of the most
intriguing examples of creative thinking on general. Its study helps us better
understand key cognitive mechanisms, the significance of representation in
problem solving and of the role of analogy in the conception of new artifacts.
It also reveals the very unique of mental imagery and of the drawing. In
addition, the study of the angle bastion in the mind demonstrates the
cooperative links between the knowledge domain of the single building and the
urban complex, each providing a harvest of design precedents bases for the
solution of new target problems as needed. Finally investigating the design of
the angle bastion sheds light into the darkness of the mind, offering a momentary
glimpse of an unexpected complex figure, two bodies clasped tightly,
inseparably, not in struggle but in a strange communion, that of Eros –
Creator, and that of Thanatos – Warrior.
NOTES
1 Much before becoming
preoccupations of military architecture associated with the fortification, the
ideas of the systemic, the optimal, the hierarchical organisation of control
and defence, the effective and efficient distribution of resources can be found
in the phalanx and in the Tactics by Polybius shaping a formless (atakton)
crowd into divisions of appropriate numbers (arithmon epitedion).
2 The angular shape
suggested is probably transfered from the koilembolon, hollow-wedge
formation of the phalanax (fig. 1c). (Asclepiodotus XI, 5).
3 The
identification of the circle as the shape which combines the maximum surface
for the minimum periphery goes back to hellenistic thinking to the formulation
of the so called "isoperimetral" problems by Zenodorus and Pappus. It
is contained in Pappus's Collection written down probably about A.D.
320. Pappus implies the economic application of his investigation in the
eloquent preface of his proof. There he pays homage to the sagacity of bees and
their talent to store honey in hexagonal hives "which would contain more
honey for the same expenditure of material" and then proceeds to the
"wider problem," and arrives at the optimality of the circle, a
problem worthy of people who "claim they have a greater wisdom than
bees".
4
"Membrification", hierarchisation means and ends, systematic
interrelation of parts which play an important role in the book, are obviously
a continuation of what Panofsky called (1957, p. 68) scholastic "mental
habit' put into a new use. Di Giorgio in the highly Aristotelian methodological
passage of his treatise refers to the philosopher as the
"calculatore". This is most probably to acknowledge his debt to the
medieval scholastic philosopher Richard Swineshead known also as "The
Calculator," whose famous Calculations were published for the first
time in Padua (1477) while Francesco was working on his treatise. One may
safely assert that Scholasticism and medieval ideas of theology contributed to
the erection not only of awesome cathedrals but also of formidable new
fortifications. It is easy to demonstrate that Alberti's and di Giorgio's
panoptic or periscopic fortifi- cation configurations, offering "continua
vigilanzia," exploited a repertory of forms originating in worlds of
divination and ritual such as the spatial schema of the omnipresent pantocrator
radiating from his seat in the middle of the sacred rotunda, surrounded
by hierarchies of archangels, apostels and saints.
5
Francesco di Giorgio's writings were not to be published until 1841 when Carlo
Promis edited them in a incomplete form, and 1976 when Maltese published it in
toto. In his short biography of Francesco di Giorgio, Vasari has noted that
the Duke of Cosimo de Medici had a copy of the book which he considered among
his choicest posessions and Leonardo da Vinci, who met Francesco di Giorgio in
Milan and in Padua in 1490, probably owned the manuscript at that period, now
in the Laurentian Library (Asburnham, MS. 361), and which Leonardo annoted in
the margin (Pedretti, 1981). Leonardo also incorporated several passages
extensively in his own manuscript treatise on fortifications which is included
in the Codex Madrid II manuscript (1974, pp. 164, 198). Although unpublished,
it is not exaggerated therefore to say that Francesco di Giorgio's writings
were not unknown and to claim that he was the father of the modem fortification
(Promis, 1841; Ackerman, 1970).
6 It is
not by chance that one of the most important contributions to the fortification
revolutions, di Giorgio's treatise, was written with the collaboration of
Federigo de Montefeltro, the famous, most well-read condottiere.
7 In
fact the closest Francesco came to designing the bastion is in another drawing
– attributed to him – in the Gabinetto delle Stampe of the Uffizi Galleries in
Florence. The drawing lies outside the corpus of the Trattati and
although as a design product it "leaves little to be added by later
military architects" (Horst de la Croix, 1960) it is too much of a
fragment to be taken as evidence that Francesco found a physical design
solution to the problem he had verbally so well stated.
8 See
Daniel Speckle in Architectura van Vestungen (1589) (fig. 7a, b, c, d),
Simon Stevin in De Stercktenbouwing (1954), written in Delft. Stevin's
text is not very original but it is remarkably acute in its argumentation and
its general observations. He had also a special interest in terminology.
"As it is always for new arts" Stevin writes, "that one gives to
new things new names", he proposed the word strijcken for aligning
fortifications with five lines from the German Streichen (Speckle, 1589)
or Italian strisciare, although Stevin retranslates the word in Italian
as scopare next to the French nettoyer, in the border of his
text.
In the
same text Stevin explicity acknowledges the role of perspective in the genesis
of the bastion. He identifies "fortresses of the present time"
("de sterckten deses tijts") as those which are "drawn most
advantageously by mathematical methods through visual rays"
("wisconstich beleyt, met
sichtstraler opt
meeste vooderelle gheteychkent worden", Stevin himself calls them on the
border of his text "radi visualius"). He praises modern
bastions (bolwercken) through which "one could destroy many
soldiers without yet breaking one's head" based upon the perspective
("Doorsichtighen, ende met de wisconsten groote gemeenschap
hebbende"). Strijcken oder strisciare of flanking as
it was also called, could not shape a bastion on its own.
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