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Buckingham Palace and St George’s Chapel, Windsor. Coade stone, under its
later owners, continued to be used until, in late Victorian times, the fashion for
polychromy ousted it from favour.
THE ARCH
An arch is a structure composed of wedge-shaped blocks, which are called
voussoirs, and designed to span a void. The blocks support each other by
mutual pressure and therefore capable of withstanding considerable weight and
thrust. A wooden framework, centering, was set up underneath the arch to
support it until all voussoirs were in position.
Parts of an arch
Often the central voussoir at the top of an arch is larger and made into an
architectural feature: this is then called a keystone. The point or line where the
arch springs up from its supporting wall or column is known as the springing
line. The lowest voussoir on each side of the arch is thus known as a springer.
The support—wall, pier or column—is the abutment. The span of an arch is the
distance between abutments and the height in the centre is the rise. The outer
curve of the line of voussoirs is called the extrados, the inner is the intrados;
the under surface is the soffit. These parts and the different forms of arch are
shown in Figure 18.3.
History of building with arches
Knowledge of arcuated construction, that is, building structurally with arches
rather than in the post and lintel manner (see p. 857), was gained by most of
the early cultures but in some of these, notably the Egyptian and the Greek,
plentiful supplies of stone and marble were available so trabeated structures
were possible. Moreover, the builders held the opinion strongly that the arch
was a less stable form of structure. Indeed, the Greeks had a proverb which
said ‘the arch never sleeps’, referring to the truism that, if the arch support
were to be weakened, the ever-present outward thrust of the curve of the arch
would cause collapse. So, in both Egypt and Greece, arcuated structures were

confined to small and utilitarian buildings.
In Mesopotamia, however, in the area between the rivers Tigris and
Euphrates, adequate supplies of neither timber nor stone were available for
building and sunbaked bricks made from the local clay constituted the chief
building material. Bricks are too small to span a lintel opening, so an arcuated
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structural system was developed for both arched openings and vaulted roofing.
The true arch, that is, one built with radiating self-supporting voussoirs, was
known here as early as 2400 BC. Sun-dried bricks are not as strong as kiln-
baked ones so the Mesopotamian structural spans of this time were not large
and, due to the softness of the material, remains are far less in quantity than
are the stone structures of contemporaneous Egypt.
In Italy the Etruscans introduced the concept of arcuated principles at an
early date, building both arched openings and vaults. A number of their fine
arched city gateways survive; most of these date from a later time, the fourth
to third century BC as, for example, that at Volterra. These structures were in
stone, as were a number of the corbelled vaults but, as in Mesopotamia,
Etruscan arcuated work was on a fairly small scale and it was the Romans,
particularly in the days of the Empire, who fully exploited the arcuated
possibilities for arcades and vaults. The facing and structure was of brick,
forming compartments, which were then filled with their exceptionally hard
concrete.
The arches so far discussed, as well as those built in the revived classical
tradition of the Renaissance and the Baroque eras, were round arches. These
might be semicircular, wherein the height of the arch above the springing line
is equal to the radius on the line or they might be segmental or stilted; in the
Figure 18.3: Arch construction.
Drawing by Doreen Yarwood.
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former case the arch is wider and lower, in the latter it is taller and narrower. A
further variant is the horseshoe arch of Islamic origin in which the curve of the
arch is carried on below the semicircle.
Romanesque architecture of the early Middle Ages (Norman, in England)
also employed the round arch. Indeed, much of the Romanesque building,
especially in Spain, Italy and southern France where remains of Imperial Rome
had survived in quantity, was strongly derivative of Roman classical work.
For most of the medieval period the pointed arch was in use and this is
characteristic of what is termed Gothic architecture. There were many
variations on the pointed form from the early, narrow lancet shape, through
the equilateral to the late, wide obtuse and to the four-centred types in the ogee
and Tudor forms.
The pointed arch is fundamental to Gothic architecture in northern Europe.
It was developed solely to provide a flexible form suited to the building of the
stone vaults which were made necessary by the hazard of fire which destroyed
many Romanesque timber roofs, causing them to have to be rebuilt time and
time again.
It was the French who introduced the pointed arch into Gothic architecture
—aptly, they call it the arc brisé, the broken arch—in the Abbey Church of S.
Denis, now in a suburb of Paris, in 1135. The pointed arch was not new. It
had long been employed in the Middle East and, in Europe, was used in areas
under Arab influence such as Moorish Spain, Sicily and Provence. The new
style originated in northern France in the area of the lie de France, because
here there was a more stable economy at the time.
The reason for the introduction of the pointed arch was that the round arch
presents great problems in vaulting a church. This is because nave, choir,
transepts and aisles often have different heights and widths. Vaulting is made in
bays and the semicircular arch lends itself to a square bay. The bay is decided by
the positioning of the supporting piers or columns. In Romanesque building the

bay was traversed at roof level by diagonals crossing one another from pier to
pier. As the diagonals were longer than the four ribs connecting the four sides or
faces of the bay, it was impossible for all of these ribs to be semicircular in form.
Either the vault had to be domical, so giving an undulating ridge rib, or the side
arches stilted. The pointed arch, which could be varied infinitely in proportion of
width to height, was far more flexible for constructing stone or brick coverings to
nave and aisles of different spans and roof levels.
THE VAULT
In building structures the term ‘Vault’ is used to describe a covered form of
roofing based upon the principle of the arch. Traditionally, over the centuries,
such vaults were constructed, as were the arches, from wedge-shaped blocks of
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stone or brick supported upon a wall, pier or column. During the nineteenth
century plaster vaults were often erected reinforced by an iron structure. In
modern architecture reinforced concrete, steel and glass fibre are among the
materials used for this purpose. As in the building of an arch, a wooden
supporting framework—centering—was erected underneath the vault to be
constructed and removed when the vault structure had been completed.
It was the Romans who first fully exploited the structure of the vault,
although knowledge of such building principles had been known to most of
the earlier cultures. Using their strong mix of concrete together with brick as
a structural and facing material, Roman builders covered very great spans
with such vaulting, particularly in their great basilicas and thermal
establishments. The vaults were massive but of the simplest forms. Three
types were used, all based on the round arch shape. Commonest was the
half-cylindrical, known variously as the barrel, wagon or tunnel vault. This
was a continuous semicircular or obtuse arch, extrapolated as in a railway
tunnel. Where two such barrel vaults of equal diameter met at right angles as
in a cruciform building, this created a square plan groined vault, the groin

being the angles of intersection. The Romans also built domes which were
generally hemispherical as in the Pantheon.
In the basilicas and buildings constructed for the bathing establishments, the
vaults were very thick. They were supported either on the also massive walling
or on heavy columns or piers. The square piers in the Basilica of Maxentius in
Romé (AD 308), for instance, measure 4.25m (14 ft) across. The majority of
important Roman vaults were coffered, that is, they were decorated by carved
octagonal, square or diamond-shaped sunken panels, partly for ornamentation,
but also because coffers reduced the weight of the vault and so its lateral
pressure upon the walls.
Romanesque builders, basing much of their church construction upon the
Roman basilican model, continued to erect round-sectioned barrel and groin
vaults but, since the knowledge of Roman concrete had been lost they dared to
cover only narrow spans. In a few instances, notably the remarkable early
example of Durham Cathedral where the choir was vaulted in 1104 (later
rebuilt) and the nave in 1135, Romanesque builders constructed rib vaults, but
these were rare, being unsuited to vaulting over square bays.
With the introduction in France of the pointed arch into vaulting design,
builders were able to break away from the constraints imposed by the square
bay. They adopted rectangular ones which, with the use of the pointed
arches, gave greater flexibility. They also constructed rib vaults in which the
stone ribs were built first, supported by centering, then the infilling between
the ribs—the web—which consisted of pieces of stone or of bricks, was
inserted. This web was of much thinner material than the Roman or
Romanesque groined vaulting had been, so rendering the whole roofing of
greatly reduced weight.
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The early rib vaults were quadripartite in design, that is, the bay roofing
was divided into four compartments by two diagonal ribs crossing one another

in the centre. On the Continent, especially in France, the quadripartite design
continued to be built for a long period but in England, often, the quadripartite
vaulting bay was divided transversely into two parts so giving six
compartments: a sexpartite vault. In most English cathedrals and churches a
ridge rib extended longitudinally along the whole interior at the roof apex level
and the rib intersections were covered by decoratively carved bosses. In France
the ridge rib was rarely used.
From the early fourteenth to the mid-sixteenth century vaulting designs
gradually became more elaborate and complex. This was especially so in
England where the last phase of Gothic architecture, the Perpendicular,
lingered late and had no parallel on the Continent. The first development was
to insert tiercerons, intermediate ribs extending from the vault springing to the
ridge rib. Exeter Cathedral is a fine example of this. Soon the lierne vault
evolved (Figure 18.4 shows a modern replica). Lierne ribs, named from the
French lier, to tie, might extend in any direction from the structural ribs and
might join any other rib. Their use was entirely decorative and later examples
are extremely complex as is evidenced in the choir vault of York Minster.
The final phase of English Gothic vaulting was the fan vault which evolved
from the desire for a structure which would accommodate ribs of different
curves as they sprang from the vaulting shaft of the capital. The radiating ribs
of the fan are of equal length and the bounding line is in the shape of a
semicircle. The whole group of ribs is made into an inverted cone, the
radiating ribs so creating a panelled and cusped all-over surface pattern. King’s
College Chapel, Cambridge (Figure 18.5), Sherborne Abbey Church and Bath
Abbey Church are supreme examples illustrating the use of this type of vault
over a long period.
An essential concomitant to the building of arches, vaults and domes was
the development of the buttress. This architectural feature is intended to
withstand a lateral force and it is arch building which particularly requires this
means to counteract the thrust which it generates. There are two chief forms of

buttressing used for this purpose. One is that pertaining to an arcade, for
example, arches extending sideways to divide a church nave from its aisles,
where each counteracts the lateral thrust from its neighbour. The other type is
where a heavy buttress is built up against the outside wall of a building to
reinforce the walls at points believed to be most vulnerable.
The Romans, who developed building with the arch and vault, constructed
strong, heavy walling, reinforced at intervals with wall buttresses to offset the
lateral pressure of their barrel and groined vaults. Romanesque builders did
the same. Gothic vaulting aroused greater problems. The buildings were
higher, the vaults high and wide and, soon, the walls were being built thinner
and being pierced by larger windows. Two types of buttress were developed.
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The tower or pier buttress consisted of a reinforcing buttress, thicker at the
base than at the top and descending in stages with sets-off from a lofty top
pinnacle to a projection at ground level of some eight to ten feet (2.5 to 3m).
The lateral pressure is felt at the top of the buttress but the sheer weight of the
massive buttress converts the thrust downwards to ground level.
As the Gothic period advanced, cathedral and abbey churches in Europe
were being constructed higher and wider and with ever larger window
openings. The usual cruciform church with nave and choir roofs built much
higher than the sloping aisle roofs meant that it was impossible to construct a
Figure 18.5: Fan vault. King’s College Chapel, Cambridge, 1446–1515.
Drawing by Doreen Yarwood.
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pier buttress between the clerestory windows to offset the thrust of the nave or
choir high vault, so the flying buttress was developed. It was discovered
empirically that the maximum thrust was to be felt at a point just below the
springing line of the vault on the interior wall so it was at this point on the

external wall face that a bridging arch was built to slope outwards and slightly
Figure 18.5: Fan vault. King’s College Chapel, Cambridge, 1446–1515.
Drawing by Doreen Yarwood.

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downwards to join a pinnacled wall buttress. This type of construction served
a dual purpose; the counterthrust at the given point on the exterior wall
conveyed the vault pressure away from the building and down to the ground;
also, by means of the heavy pinnacle above, it helped to offset the vault thrust.
In very complex church designs, where five aisles had been built, a double
flying buttress system had to be constructed with arches spanning each of the
two flanking aisles. The French architects developed the flying buttress and it
is in France that the eastern arm chevet of a cathedral displays the elegant and
dramatic forest of arches and pinnacles which are so impressive. In England,
with lower vaults and roofs, flying buttresses were needed less and are most
evident in the later buildings of the fifteenth and sixteenth centuries as, for
example, at the Henry VII Chapel of Westminster Abbey in London.
With the introduction of Renaissance architecture and the return of
classicism the domed covering became more common than the vault. In
modern times, however, the development of new materials has made possible
the erection of thin shell vaults of half-cylindrical or barrel form which may be
extended over long spans without requiring piers which obstruct the interior
vista. These are particularly suitable for industrial, sports or entertainment
purposes. Reinforced concrete, lightweight metals such as aluminium and
plastics reinforced with glass fibre are the most usual materials for this.
THE DOME
A dome is a convex rounded roof covering the whole or a part of a building
witha base on the horizontal plane which is circular, elliptical or polygonal. In
vertical section the dome may be hemispherical, partly elliptical, saucer-shaped

or formed like a bulb (the so-called onion domes to be seen in eastern Europe).
The English word dome derives from the Latin domus, a house, and the Italian
duomo, cathedral, or House of God. It has been traditional in Italy to build
domes over churches and so ‘dome’ had been adopted for this meaning in
England. The more usual Italian term is cupola, derived from the Latin cupula,
diminutive of cupa, flask, barrel.
While the Romans extensively developed the theme of the arch and the
vault they largely neglected the possibilities of domical coverings. They were
the first to build domes in western Europe but these were most often supported
on buildings with circular walling as in the most famous example, the
Pantheon in Rome. Begun in AD 120, this has a very large dome—43m (142
ft) in diameter —which is hemispherical in form. Its continuous thrust is
contained by the 6m (20 ft) thick cylindrical walling into which it is embedded
and further support is provided by stepped rings of masonry encircling it above
wall top level. This results in an uninterrupted view of the dome from inside
the building, but on the exterior only the upper part is visible.
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The Romans also covered square interiors with groined vaults, as in their
bathing establishments and it is thought that they knew how to build a
domical vault over a square space. This is a domical form made of four webs
separated by groins which fuse to a point; it is not a true dome and its design
lacks flexibility of proportion. Building a dome over circular walling
presented fewer structural problems but limited the spatial capabilities of
interior architectural design.
In Renaissance and, even more so, Baroque architecture, the dome became
a fundamental characteristic of design and a variety of different forms of
construction were attempted and built. To achieve, in particular, the Baroque
spatial effects of lighting and of solid stone structures ornamented by painted
and sculptured curved surfaces appearing to float upwards, it was necessary to

support the dome upon free-standing piers instead of the more constricting
walling. The basis for this type of construction was the Byzantine development
of the dome, evolved in Constantinople, capital city of the Byzantine Empire, a
construction which, in its turn, had derived from earlier buildings in
Mesopotamia, Anatolia, Persia and Syria.
The essential problem in building a dome of circular section upon a drum,
also of circular section, which can contain windows to light the interior, over a
square is to transform the square base into a circle upon which the drum can
be supported. This may be achieved two different ways: by the use of the
squinch or the pendentive. Both methods derive from Asia; the former can be
seen in extant remains as early as the fourth century in Persia, the latter in
Syria and Asia Minor. In squinch construction an arch, or series of arches, is
built across the upper angles of the square to transform the square base to an
octagonal one and so more easily support a circular base. This method was
extensively employed in the Byzantine period and later in both east and west,
for example, in the cathedral at Le Puy in France.
The pendentive is a more ambitious and imaginative, as well as more
successful, solution. It was widely used in the best Byzantine building, from
S.Sophia in Constantinople (built 532–8 by the architects Anthemios of Tralles
and Isodorus of Miletus) onwards, and has been the basis of dome
construction in the west from the Italian Renaissance to the present century. A
pendentive is a spherical triangle. In using this form of construction the
triangular spaces between the square section of the plan of the piers and the
circular section of the base of the dome are built as if they are parts of a lower,
larger dome, so their section is like that of an arch carried across the diagonal
of the square space to be covered. The lower dome possesses a horizontal
section which is concentric with the plan of the intended dome. As the lower
dome is too large to fill the square space, it is cut off in vertical planes formed
by the four sides of the square. When the four remaining parts of the lower
dome have been built high enough to form a complete circle within the square

section, this circle provides the basis for supporting the actual dome. If this
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design is not further developed it is known as a sail vault because it gives the
appearance of a sail filled with wind anchored at the four corners.
If the dome set upon pendentives is further constructed, the drum of the
dome is set upon the circular section of the lower dome and the drum carries
the upper dome. Externally most large domes carry a lantern. Internally the
drum is articulated with a classical order and windows while the pendentives
and dome are decorated by paintings and/or mosaics.
Renaissance domes
It was accepted by the classical architects that a hemispherical dome provided
the most satisfactory exterior silhouette from the aesthetic viewpoint. This,
however, created problems. These were partly of a structural nature, because a
hemispherical dome exerts a particularly strong thrust. They were also of a
visual character because, while externally the hemisphere provides a pleasing
shape and an imposing landmark, internally it is too tall and dark and its
decorative covering of paint or mosaic cannot readily be seen. The solution,
adopted by many architects, was to build two domes, a taller exterior one and
a lower interior one.
The first great Renaissance dome was the one built by Filippo Brunelleschi
to cover the unfinished medieval Cathedral of Santa Maria del Fiore in
Florence. To this commission Brunelleschi had to bring his considerable
knowledge of mathematics and of the structure of Roman vaults. The practical
problem for this early date (1420) was considerable: how to construct a
permanent dome to span the 42m (138 ft) diameter space. Brunelleschi dared
not build a hemispherical dome on the existing drum, which had no external
abutment, so he compromised and proceeded step by step. His dome is a
pointed one, constructed on Gothic principles with ribs supporting a lighter
infilling, and is taller than a hemisphere to offset the thrust. He then built an

inner dome of slightly less height which is decoratively painted on the interior.
Michelangelo faced not dissimilar problems with St Peter’s Basilica in
Rome. His exterior design was for a hemispherical dome but when this was
completed in 1590, after his death, by Giacomo Della Porta, it too had
acquired a slightly pointed form. Michelangelo raised his great dome, also of
42m (138 ft) diameter, almost as large as that of the Pantheon, upon a classical
drum and supported both drum and dome on four pendentives rising from
four massive piers set at the church crossing. Unlike the Pantheon, however,
there was no supporting enclosing circular wall, so Michelangelo encircled the
dome with iron chains, which have had to be replaced ten times since the
original construction in order to contain the thrust.
At St Paul’s Cathedral in London (completed 1710) Sir Christopher Wren
supported his smaller drum and dome 34m (112 ft) diameter upon eight piers.