APSE VAULTS
The traditional method of terminating the church edifice at the end
reserved for the clergy was by means of a semicircular or polygonal
apse, and this method, which was of Roman origin, continued to be
followed in the majority of Romanesque and Gothic churches. Such apses
gave to the interior of the edifice a more dignified appearance than was
possible with a flat east wall, by avoiding the abrupt termination which
the latter produced and by emphasizing the central point in the
sanctuary, which was occupied by the high altar in most of the mediaeval
churches.
APSES VAULTED WITH HALF DOMES
Once adopted from Roman architecture as a standard part of the church
plan, the construction of the apse was naturally based upon Roman
models, and since these were always vaulted with a half dome of masonry,
similar half domes were employed by the Christian builders of the early
mediaeval period. During the Romanesque era, these half domes were
almost always of stone laid in horizontal courses, supported by
substantial walls of semicircular or polygonal plan. They opened
directly into a transept or a tunnel-vaulted choir. The earliest of
these half domes were of semicircular elevation, but the pointed form
made its appearance in the late eleventh or early twelfth century in
many churches. In both forms, the principles of construction are the
same.
LIGHTING PROBLEMS CONNECTED WITH THE CONSTRUCTION OF HALF DOMED APSES
It is a characteristic of the half dome that it exerts a large amount of
downward pressure and but little outward thrust, particularly if it be
of pointed section. For this reason, such a vault requires a firm
support but only a slight amount of buttressing. As long, therefore, as
the half dome rested directly upon comparatively low exterior walls, it
had plenty of support, and it was even possible to pierce the walls with
windows without endangering its stability. But with the increase in
height of the more developed Romanesque churches and the introduction of
ambulatories, it became difficult to light the sanctuary and still
retain the half dome.
Two methods were evolved for overcoming this difficulty. The first,
which may be seen in the abbey church at Cunault (Maine-et-Loire)
(second half of twelfth century),[339] consisted in the construction of
a lofty ambulatory opening into the apse through arches rising to the
impost of the half dome, or even slightly above it, and resting upon
piers of as slender proportions as possible, so that, although the
sanctuary was deprived of all direct light, a certain amount was
obtained from windows in the outer wall of the ambulatory or from the
radiating chapels, while, at the same time, the vault of this ambulatory
aided in the support of the apse and vice versa. Such a system, though
structurally correct, was not entirely satisfactory. The sanctuary and
choir were the portions of the church most in need of lighting, since
they contained the altar and the seats for the monks or clergy by whom
the services were chanted, and indirect light was bound to be
insufficient.
The second method, which may be seen in the church of Saint Savin
(Vienne) (eleventh century),[340] consisted in reducing the height of
the ambulatory, even when this involved making it lower than the side
aisles, and then placing a clerestory above the ambulatory arches
beneath the springing of the half dome. This may be considered as the
best type of apsidal termination developed during the purely Romanesque
period. It was only when the half dome was discarded that a satisfactory
solution was finally reached in the development of the chevet vault.
There were, however, two important series of ribbed half domes, the
second of which, at least, may have had some bearing upon the evolution
of the chevet type.
APSES WITH RIBBED HALF DOMES
The first series lies largely in southern France in the Romanesque
school of Provence. Here there are a certain number of churches, among
them the chapel of Saint Honorat in Les Alyscamps at Arles
(Bouches-du-Rhône) (eleventh century?), in which the surface of the half
dome is broken out at regular intervals into a number of flat,
pilaster-like, radiating strips, forming a part of the actual masonry of
the vault. These divide the half dome in much the same manner as true
Gothic ribs, but they do not support it in any way and seem to have been
used for the decoration which such a change in the surface of the vault
produced.[341] As a general rule, these ribs radiate from a point
slightly back from the crown of the apse arch and often from a raised
masonry ring as in the chapel just cited. They vary, however, both in
number, thickness and width, some being comparatively thick and widening
out from the central keystone as in the cathedral of Notre Dame-des-Doms
at Avignon (Vaucluse), others being but slightly salient and of the same
width throughout like those in Saint Honorat at Arles.
Much larger in number and extent is the second series of churches with
rib-vaulted apses, though they are in general of later date than those
in Provence. Their radiants have a certain structural character, for
they are independent of the vault surface and were doubtless erected in
most cases as a permanent centering to aid in the construction of the
half dome. They do not, however, aid to any extent in its support, for
the courses of masonry in the vaults are still horizontal and concentric
with the curve of the apse, and the completed half domes would therefore
stand just as well were the ribs removed. It may be that they were
introduced in order to make the apse correspond more closely in
appearance with the ribbed vault which had in many cases been introduced
in the naves of the churches in which the ribbed half domes are found.
In any event, they mark a stage in apse vaulting between the simple half
dome and the developed chevet, which is worthy of careful consideration.
Most of these vaults date from the second quarter of the twelfth century
and are to be found within the zone of influence of the Ile-de-France,
though occasionally an example is found at a long distance from this
center as in the case of Sant’ Abondio at Como,[342] Santa Maria di
Castello at Corneto-Tarquinia in Italy,[343] and such churches as that
of the Monasterio de la Oliva (Navarra) in Spain,[344] (1198). The
number of ribs varies considerably, though two is most common
particularly in the smaller churches and chapels.[345] Of these, the
church at Morienval (Oise) (Fig. 77) furnishes a good, though recently
reconstructed, example, while Saint Georges-de-Boscherville (Fig. 61)
may be cited as possessing a large apse of similar character.
The important thing in a comparison of these two vaults is the
difference in the lighting of the completed apse. At Boscherville, it
was a simple matter to pierce the exterior wall with windows, in this
case in two stages, and still keep their crowns practically below the
level of the impost of the half dome, since the latter rested directly
upon the outer walls. But at Morienval there was an ambulatory, and in
order to get a clerestory above its arches, the windows had to be cut
into the curved surface of the half dome itself, with the result that
they were so deep as to prove of only limited usefulness. Other examples
could be cited where this same attempt is made to obtain sufficiently
large windows by shoving their heads into the half dome,[346] while at
Beaulieu (Corrèze)[347] the windows lie entirely above the impost.
Besides the ribbed half dome just described, there is still another type
to be seen in the Lady chapel of the church of Saint Martin-des-Champs
at Paris (Fig. 65). Its plan is a trefoil and the vault is made up of a
series of segments of domes with salient ribs marking their
intersections. As far as construction is concerned, there is really no
change from that of the more common half dome, for the courses of
masonry are still horizontal and the ribs merely serve as centering and
as a means of subdividing the surface to be vaulted and clearly marking
the lines of intersection. The vault would stand equally well were the
ribs removed and is, in structural character, very similar to the celled
domes of the Villa Adriana at Tivoli and of S.S. Sergius and Bacchus at
Constantinople.
[Illustration: FIG. 61.--SAINT MARTIN-DE-BOSCHERVILLE, SAINT GEORGES.]
“GROINED HALF DOMES”
Another form of apse vault of which there would seem to be a number of
examples prior to the introduction of ribbed vaulting may perhaps be
termed the “groined half dome.” It is a vault resembling a segmental
dome except that the segments do not run down to a common impost, but
form a series of window cells not unlike those of a groined vault but
not running all the way to the vault crown. The earliest of these vaults
appears to be that in the crypt of Saint Laurent at Grenoble (Isère)
(sixth century).[348] Rivoira has shown[349] that Roman prototypes of
this form can be found in the so-called “Temple di Siepe” (second
century) at Rome, the vestibule of the Villa Adriana at Tivoli (125-135)
and elsewhere. There are also a number of Romanesque examples. Of these,
one is in the chapel off the south transept of Saint Nicholas at Caen
(1080-1093),[350] while another is to be found in Saint Andrew’s chapel
at Canterbury cathedral (cir. 1110).[351] These vaults closely resemble
the true Gothic chevet which was soon to follow them, and they might
seem to be its prototypes were it not for the fact that their
construction is of an entirely different character. All are built of
small stone or rubble and were undoubtedly laid up on a wooden centering
with no particular regard for the direction in which the masonry courses
ran, or possibly with these courses like those in a half dome. The
construction was thus a combination of half dome and groined vaulting
and not at all of the ribbed type. That they may, however, have been of
influence in the development of the true chevet will be later suggested.
APSES WITH FOUR-PART RIBBED VAULTS
A final type of rather primitive vaulting which was subsequent to the
introduction of ribbed vaulting but would seem to be prior to the use or
at least to the extensive knowledge of the chevet, consisted in the
employment of a simple four-part vault over the semicircle of the apse
(Plate II-a).[352] The result was an awkward kind of chevet vault which
is worthy of consideration as perhaps having a part in the development
of the true Gothic form. It might properly be called a four-part
cross-ribbed apse vault.
[Illustration: PLATE II]
THE CHEVET VAULT
By the middle of the twelfth century, all the methods of apse vaulting
thus far described, were abandoned[353] in favor of the ribbed Gothic
chevet[354] which was then developed. In this new vault the masonry
courses are no longer horizontal and concentric but run in a generally
perpendicular direction from a series of radiating ribs, which have a
common keystone, to a wall rib or a curved line of intersection above
the heads of a series of apse windows in whole or in part above the
level of the impost of the radiants. In other words, the chevet vault
consists of a series of triangular severies, each essentially like one
quarter of a four-part cross-ribbed vault.
The evolution of this developed chevet from the earlier types of apse
vaulting already discussed is difficult to trace and in fact it seems
most reasonable to imagine that it was a spontaneous transformation
which did not require any intermediate steps. It has, for instance, been
pointed out that the greatest problem of the apse builder was to place a
clerestory of good sized windows above the ambulatory arcade or at least
as high as possible in the apse wall and at the same time to keep the
pressures and thrusts of his vault at the lowest possible point. Imagine
then a builder with this in mind starting to construct a ribbed half
dome with windows rising above its impost. Suppose that the radiating
ribs were first constructed and the space to be vaulted thus divided
into triangular compartments. Now assume that the builder was familiar
with the four-part cross-ribbed vault--a reasonable assumption since
everything seems to point to an earlier date for such vaults than for
the ribbed chevet. Would he not be prompt to see that a series of
clerestory windows could be built around the apse precisely like those
along the walls of nave or choir and each triangular space thus formed,
be covered by one quarter of four-part vault? Is not this especially
reasonable in view of the fact that there existed groined vaults of just
this type,[355] exactly as there existed groined prototypes out of which
sprang the simple four-part cross-ribbed vault? Furthermore, if the
peculiar four-part apse vaults described as sometimes employed in
transitional churches are any or all of them earlier than the earliest
of the true chevets, would it not seem as if the builders were bent upon
using quadripartite vaulting of some form, even over the apse, in order
to obtain a clerestory? Whatever the true process of evolution may have
been, it is at least possible that the above explanations are correct
and that the chevet vault developed directly from the difficulty of
placing windows beneath the ribbed half dome. If such was the case
another type of vault would seem to have owed its origin in large part
to the lighting problem.
TYPES OF CHEVET VAULTS
Once introduced, four types of chevet vault were gradually established,
not counting the variation which each of them underwent. For convenience
these will be called the radiating-ribbed type, the broken-ribbed type,
the buttressing-ribbed type, and finally the diagonal or cross-ribbed
type. Each will be considered in turn and an effort made to trace their
consecutive development.
The chronology of these vaults is very difficult to determine. In fact,
it is probably safe to assume that the earliest example, if there were
not a number of these vaults simultaneously constructed, has
disappeared. In any event, it would seem that the vault must have been
first used somewhere between 1130 and 1150 as there are several existing
examples which date from this period. If these cannot be arranged in any
certain order, they may at least, be used to show the form of the early
chevets.
RADIATING-RIBBED CHEVETS
Perhaps the most primitive, in appearance at least, is that above the
transept of Tournai cathedral (Fig. 53) in which, as has been
noted,[356] the extrados of each rib is built up until it forms a flat
sloping upper surface, each cell of the vault proper rising from the
ramps thus formed. Next to this vault at Tournai, and as a matter of
fact, probably of earlier date though of more developed type are the two
chevet vaults of Largny (Aisne) (cir. 1140).[357] and Azy-Bonneil
(Aisne),[358]--which are three-celled,--and the one in the lower story
of the chapel of the Bishop’s palace at Laon (cir. 1137-1147) (Fig. 62)
with five cells. The latter shows their general characteristics. There
are no wall ribs and the round-headed windows are only partly raised
above the impost of the radiants while there abut against the keystone
of the apsidal arch (Plate II-b). It will be noticed also that this arch
is greatly thickened to resist the pressure of these ribs, and at
Tournai is preceded by a tunnel-vaulted bay to make this resistance even
more secure.[359]
[Illustration: FIG. 62.--LAON, CHAPEL OF THE BISHOP’S PALACE.]
But much more important than these smaller chevet vaults, are those of a
number of large churches, also belonging to the second quarter of the
twelfth century. Of these, Saint Germer-de-Fly[360] (Fig. 63) has been
most prominently brought to notice through Mr. Moore’s work on Gothic
architecture. It is doubly of interest because it possesses chevet
vaults of two distinct stages in the development of this new form. Thus
in the original radiating chapels opening off the ambulatory,[361]
three-part chevet vaults of the type described in the previous
paragraph were employed, with this advance, namely the introduction of
stilted, round-headed wall ribs. The vaults are still highly domed at
the crown and it would seem very reasonable to suppose that they were
completed before the vault of the great apse was begun.
[Illustration: FIG. 63.--SAINT GERMER-DE-FLY, ABBEY CHURCH.]
This latter shows an advance in construction beyond that hitherto seen.
In the first place, the entire window is placed above the level of the
impost of the radiants with a consequent raising of the vault surface
above the windows and a great reduction in its domed-up character. The
line of intersection of the vault cell with the apse wall, which is
marked by a slightly pointed, stilted wall rib, resting upon slender
shafts rising from the clerestory string-course, is almost perpendicular
from the impost of the radiants to a point about at their haunch. Thus
the lower portion of the masonry panel is really a flat wall resting
upon the ribs. The object of the builders in thus constructing their
vault panels would seem to have been twofold, first to get a large space
of pleasing shape for clerestory windows and secondly to aid in
overcoming the thrusts of the radiating ribs. The first is perhaps the
less important of the two, for the windows in the early chevets very
rarely occupy all the space beneath the wall intersection. The second,
however, furnishes a much better explanation of this form of panel. And
this explanation would seem to lie, not so much in the fact that the
stilted wall rib concentrated the thrust along a narrow strip of
exterior wall where it could be met by exterior buttresses[362] but
rather in the fact that the weight of such a flat wall, rising
perpendicularly above the radiating rib, practically offset all of their
outward thrusts by its downward pressure while the little which remained
was taken care of by the thick walls characteristic of church
construction in the Transitional period. Thus it is possible to account
for the almost total lack of exterior abutment in such apses as this at
Saint Germer-de-Fly, where only the slenderest of shafts are found along
the exterior wall serving far more for decoration than for
abutment.[363] That the stilting was not done primarily to concentrate
the thrusts is further shown by the fact that in many of the later
Gothic churches which were built long after the flying-buttress was
perfected there is no attempt to stilt the wall rib, but the masonry of
the vault is actually curved outward from the very springing of the
radiants, which are raised to the impost of the window heads to give the
vault this form.[364]
The highly stilted wall intersection with the consequent elevation of
the clerestory window and flattening of the lower part of the vault cell
constitutes the great structural advance in the chevet of Saint Germer.
The employment of the wall rib, however, introduces an important matter
for discussion. To be sure this is not by any means the first example of
its use, for formerets may be found even in groined vaults, but it is
one of the early examples on a large scale and may serve to introduce
the question as to the part which these ribs played in Gothic
architecture.
THE USE OF WALL RIBS IN GOTHIC RIBBED VAULTING
It has generally been maintained that the wall ribs were integral and
important members of a true ribbed vault and that they actually aided in
the support of the masonry panels. There are, however, a number of
reasons for believing that this is not entirely so but that these ribs
were comparatively unimportant as far as their relation to the vaults
was concerned and were of much more importance, in the first place as
cover joints, in the second as window heads, and in the third as
relieving arches in the clerestory wall. Two important facts lend
strength to the theory that the wall rib was not as a rule a supporting
member. The first of these lies in the fact that it was quite frequently
omitted even from vaults of the true Gothic form, and the second, in the
fact that, when present, there are perhaps as many cases in which the
curve of the vault fails to follow that of the rib as there are of the
reverse condition. In fact, it is a question whether in the majority of
cases the vault panel actually rests upon or even cuts into the face of
the formeret. Take, for example, a number of chevet vaults[365] and
examine them in this respect. At Saint Germer (Fig. 63) the wall rib is
largely a relieving arch in the clerestory wall which is made much
thinner beneath it; and while the curve of the chevet cells follows in
general that of the arch, it does not exactly correspond with it. In the
large chevet vault of Saint Remi at Reims (Fig. 64), and in many other
vaults not over the apse, especially in the English churches and those
in which a group of clerestory windows is found in each bay, no wall rib
is used, showing that such a rib was not at all necessary as far as the
construction and support of the vault was concerned. Moreover, in many
of the churches in which a wall rib is used along the exact line of the
vault surface, it is too small to act as a supporting member and would
seem to be merely a cover-joint to hide the intersection of the vault
surface with the clerestory wall.[366] Finally and most important of all
are the cases in which this rib is used primarily as a window head. In
some of these, as for example in the apse of La Madeleine at Vézelay,
and those of the cathedrals of Soissons (Fig. 67) and Chartres (Fig.
68), the curve of the vault corresponds with this window-head arch, but
in many other apses such as those of Bourges cathedral (Fig. 76), of
Saint Étienne at Caen (Fig. 70), and of the Sainte Chapelle at Saint
Germer, the builders without hesitation curved their vault surface away
from the line of the window-head which would otherwise be the natural
wall rib.[367] Although from the preceding facts, it would seem evident
that the wall rib was not an essential structural member of the Gothic
vaulting system it may have been of advantage in many instances for
holding a temporary wooden centering during the construction of the
vault panels.
[Illustration: FIG. 64.--REIMS, SAINT REMI.]
RADIATING-RIBBED CHEVETS CONTINUED
Returning again to the radiating-ribbed chevet, especially that of Saint
Germer-de-Fly (Fig. 63), it is important to note the one great weakness
which this vault possesses. It lies in the position of the radiating
ribs which abut the apsidal arch at its crown, in other words at a point
not at all suited to meet the pressures which are thus brought to bear
against it. A rather heavy arch between the apse and the remaining bay
of the choir, though no heavier than those in the vaulted bays of the
nave, aids in resisting the pressure but nevertheless such a vault is
not strictly logical from a structural standpoint. It is not as well
buttressed, for example, as the ribbed half dome of Saint Georges at
Boscherville (Fig. 61), or the transept chevet at Tournai (Fig. 53), in
which a tunnel vaulted bay precedes the arch against whose crown the
radiants are brought to bear.
It is not surprising that this vault was but little used in subsequent
Gothic architecture. It is possible, however, to cite a few examples,
among them the cathedrals of Séez (Orne) (end of the thirteenth
century), Cambrai (Nord) (cir. 1250), and Dinan (Côtes-du-Nord) (end of
the thirteenth century), the cathedral of Saint Sauveur at Bruges
(Belgium) (probably thirteenth century), and the abbey church of Moissac
(Tarn) (probably fourteenth century). There is also a peculiar form in
which the ribs are narrowed toward the crown, in Santa Maria sopra
Minerva at Rome (after 1285). Two other slight variants of the type, one
in the church of Saint Pierre-le-Guillard at Bourges and the other in
the cathedral of Moulins are later discussed.
BROKEN-RIBBED CHEVETS
After that of Saint Germer-de-Fly, perhaps the next important chevet is
that of Saint Martin-des-Champs at Paris (Fig. 65), which dates from
about 1140-1150 and may possibly be the earliest of what will be termed
broken-ribbed chevets. On the exterior, this apse closely resembles
Saint Germer with no flying-buttresses and only very light exterior
buttress-shafts. In the interior, however, there is a marked difference
between the two, for the apse of Saint Martin-des-Champs is so
constructed as to include not merely the bays actually on the curve, but
one rectangular bay of the choir as well. The builders thus set
themselves the problem of constructing a chevet vault with seven cells,
over a space greater than a semicircle. If they had made all the
radiants of such a vault meet at the crown of the transverse arch, there
would have been a great disparity in the length of the ribs and a very
awkward shape to the separate vault cells. To avoid this, and to do away
with the pressure of the radiants at the crown of the apsidal arch, the
builders moved the keystone of the radiating ribs back from this crown
to a point where all of them become nearly equal in length. And since
the bay with parallel sides was of practically the same size as
four[368] of those making up the apse proper, the keystone fell very
nearly on the transverse line between the two piers marking the eastern
end of this bay (Plate II-c). In none of the chevets of this type did it
fall directly at the center of such a line, however, and it is this fact
that differentiates the chevet vaults of broken-ribbed character from
the slightly later and more developed buttressing-ribbed type. A vault
like that at Saint Martin-des-Champs, marks an advance over that at
Saint Germer in that the two western ribs furnish admirable abutment for
the keystone of the vault, and the added choir bay gives a more spacious
appearance to this portion of the church.
[Illustration: FIG. 65.--PARIS, SAINT MARTIN-DES-CHAMPS.]
There is another example of this broken-ribbed chevet in Paris, in the
church of Saint Germain-des-Pres (cir. 1163), while still others may be
[Illustration: FIG. 66.--VÉZELAY, LA MADELEINE.]
seen in Saint Quiriace at Provins (cir. 1160) (Fig. 31) and in La
Madeleine at Vézelay (cir. 1140-1180) (Fig. 66). The latter is of
especial interest because it shows some peculiar makeshifts in the
matter of construction. Here the choir would seem to have been
originally designed to consist of two rectangular bays with four-part
vaults and an apse of five sides probably with a chevet like that at
Saint Germer.[369] But by the time the western bay of the choir had been
built up to the clerestory, it would seem as if a new idea of a
seven-part chevet had come in, perhaps from Paris, and the next bay was
subdivided so as to give seven equal sides to the new vault. Then to
make all the bays of the same scale, the west bay was also subdivided,
but this necessarily at the clerestory level, and covered with a
six-part vault. This left nine bays for the chevet and as only seven
were to be actually included beneath the radiants, a narrow rectangular
four-part vault was used over that toward the choir. There now remained
an apse in all respects like those of Saint Martin-des-Champs and of
Saint Germain-des-Pres and it was similarly vaulted with a broken-ribbed
vault whose keystone does not lie quite upon the transverse line between
the first two piers of the apse proper. The chevet built upon these
radiants differs, however, from those in Paris and at Saint Germer in
having a decidedly domed up character. In other words, the windows do
not rise more than half the distance from the impost of the radiants to
their keystone.[370]
BUTTRESSING-RIBBED CHEVETS
This type of chevet as developed at Paris and Vézelay played a large
part in subsequent architecture, for out of it would seem to have sprung
what will be for convenience termed the buttressing-ribbed chevet. Among
the more important early chevets of this type are those over the apses
of Noyon[371] transepts, of Saint Remi at Reims (Fig. 64), of Saint Leu
d’Esserent (Oise), and of the cathedrals of Sens, Canterbury, Noyon, and
others, all probably completed before 1180. Although differing in a
number of details, these apses have certain features in common. They all
include beneath the chevet the preceding bay of the church, and all have
the same arrangement of ribs which are so placed that the two springing
from the piers next beyond the apsidal arch on either side form a
transverse arch against whose crown all the others abut (Plate II-d).
The object of this arrangement evidently lay in the desire of the
builders to construct a distinct transverse arch between the curve of
the apse and the rectangular bay included in the chevet and at the same
time to employ the two ribs beyond those forming the arch, as
buttresses, to offset the thrust of the remaining radiants. Thus when
the rectangular bay was larger than those around the curve, as for
example in the choir of Soissons cathedral (Fig. 67), the buttressing
ribs were longer than the remainder of those forming the vault. This
made the bay containing these two ribs precisely like one-half of a
six-part vault, and as this method of vaulting was commonly used in the
nave and choir of these churches this chevet was a very
[Illustration: FIG. 67.--SOISSONS, CATHEDRAL.]
logical continuation of such a vault. But the builders do not seem to
have realized immediately the aesthetic advantage in so planning their
churches that such chevet vaults should come next to a six-part vault.
At Sens (Fig. 28), however, the perfected use of this new chevet is
shown for it is placed directly beyond a six-part bay and its two
buttressing ribs are the counterparts of the two diagonals of the
sexpartite vault. Once the advantage of such an arrangement was grasped,
the churches were in many cases planned to provide for an even number of
six-part bays in the choir followed by a chevet which carries the same
system into the apse of the church. Thus in the cathedrals of Paris and
Bourges, and probably originally in that of Soissons, as well as in
other churches with six-part vaulting, this chevet became the standard
form of eastern termination and the bay preceding the apse was made
sexpartite so that the completed church would be uniform
throughout.[372] Moreover the apsidal bays of the later chevets, as for
example that at Soissons (Fig. 67) were frequently so planned that the
radiants from the piers next beyond the ribs forming the transverse arch
containing the keystone, were exact extensions of the buttressing ribs.
In other words, except for the subdivision of the eastern bay into three
window cells, the chevet corresponded to a true six-part vault inscribed
in the space formed by the last bay of the choir and the polygonal-sided
apse.
Notwithstanding the fact that the buttressing-ribbed chevet was
primarily suited to churches with six-part vaulting, it was by no means
confined to these for it is found in a large number which were from the
beginning planned for four-part vaults. Among these is the cathedral of
Rouen, in which the chevet is of distinctly six-part type with a
full-sized choir bay included beneath the vault,[373] and the cathedral
of Reims in which all the bays of the chevet are of practically the same
size, as in the early churches which gave rise to this form of apse
vault. Reims is thus an example of the perseverance of the design of a
seven-sided chevet including one bay with parallel walls and yet of the
same size as those forming the curve.[374]
But while pleasing in appearance when used in combination with six-part
choir vaults, the chevet with buttressing ribs was not so satisfactory
in churches with four-part cross-ribbed vaulting of rectangular plan. A
reference to the vault of Soissons cathedral (Fig. 67)[375] will
illustrate the faults of such a combination. These lie largely in the
three-part vaulted bay. In the first place, though its window cells are
practically the same width as those in the remainder of the choir, their
crown lines run out at an awkward angle,[376] instead of being
practically perpendicular to the outer walls as in the remaining bays of
the apse and all those of four-part type. Secondly, the great,
triangular, transverse severy is much larger than any of the others in
the church and is thus unpleasing when contrasted with them, besides
being more difficult to construct because of its larger size. It is not
surprising to find, therefore, that a fourth form of chevet was
developed and used extensively in churches with four-part vaulting.
This chevet, which will be termed diagonal-ribbed, is perhaps the most
important distinct type developed in Gothic architecture.
DIAGONAL-RIBBED CHEVETS
[Illustration: FIG. 68.--CHARTRES, CATHEDRAL.]
It has already been noted that there were a number of early apses
covered with an elementary kind of chevet which was formed by the use of
two diagonal ribs over the semicircle of the apse in exactly the same
manner as similar ribs were used in rectangular four-part vaulting. Such
a vault as this may have been the prototype of the slightly more
developed form to be seen in the radiating chapels of the cathedral of
Noyon (before 1167)[377] and in the chapel at the end of one aisle of
Notre Dame at Étampes (Seine-et-Oise) (cir. 1160). This latter has one
extra rib added in what would have been the eastern bay of such a
four-part apse vault subdividing it into two window cells and thus
producing a four-celled chevet[378] (Plate II-e). It is exactly this
principle, applied on a larger scale and with a further subdivision of
this outer bay, which may be seen in such chevets as those of Chartres
cathedral (Fig. 68) and Saint Étienne at Caen (first quarter of
thirteenth century) (Fig. 70).[379] Of these, the one at Chartres has
the more primitive character, for all of its seven bays are on the curve
of a semicircle and thus none of the choir proper is included beneath
the chevet (Plate II-f). As a result of this increased number of bays,
the intersection of the two diagonal ribs which form the first two
radiants on each side, lies at a point comparatively near the keystone
of the apsidal arch. This gives a certain uniformity to the size and
character of the bays, but the vault is not yet perfect, for the ribs
are still noticeably different in length, and more important than this
the crowns of the window cells are at an awkward angle with the exterior
wall. These faults are, however, much less marked in Saint Étienne,
where the apse is greater than a semicircle--though even this chevet is
not of the perfected diagonal-ribbed type, since it has no wall ribs
and, moreover, is used over an apse of semicircular instead of polygonal
plan like those of the developed Gothic period. An example of the
perfected vault may be seen, however, above the apse of Amiens cathedral
(Fig. 69). Here there are but five bays of the chevet along the curve of
the apse proper, the remaining two being continuations of the choir
walls (Plate II-g). The diagonal ribs which determine the position of
the keystone are therefore precisely such ribs as those in the remainder
of the chevet except that the bay in which they lie is of smaller size
than those preceding it and thus forms a gradual transition to the still
smaller bays comprising the apse proper. As a result of this arrangement
of ribs at Amiens, the keystone of the vault is so placed that it not
only renders all the radiants of practically equal length but also makes
the crown lines of each window cell so nearly perpendicular to the wall
as to give a most symmetrical effect to the entire vault. Such a chevet
constitutes the finest method of apse vaulting developed in Gothic
architecture and in fact may well be considered the most perfect type
conceivable, at least from the point of view of appearance. It loses a
little in structural character through the fact that the first ribs do
not abut the four eastern radiants at as firm an angle as in the
previous chevet type,[380] but the advantage gained in the more
symmetrical character of the vaulting severies makes up in large degree
for this possible fault.
CHEVETS WITH ADDED RIBS
[Illustration: FIG. 69.--AMIENS, CATHEDRAL.]
Nevertheless it may have been a feeling on the part of the builders that
there was a lack of abutment to the west of the keystone which led to
the introduction of one or more short ribs at this point in a number of
chevets of various dates throughout the Gothic era. Thus in the apse of
Saint Étienne at Caen (Fig. 70),[381] of Saint Trophîme at Arles, and of
the cathedral of Notre Dame at Mantes, a single rib runs out from the
keystone of the chevet to that of the apsidal arch. (Plate II-h). Nor
was this rib a continuation of a ridge rib in the choir, for in the
instances just cited no such rib was employed. One is to be seen in a
number of churches, among them such widely separated examples as San
Saturnino at Pamplona,[382] Westminster Abbey,[383] and Saint Alpin at
Chalons-sur-Marne.[384] All of these churches have diagonal-ribbed
chevets, but there are instances of a short rib running to the apsidal
arch even where the vault is of the buttressing ribbed type, as for
example in the cathedral of Barcelona,[385] where it would seem to have
been used to subdivide the great triangular transverse cell of the vault
even more than to provide further apparent abutment for the other
radiants (Plate II-i). Even in chevets of the first type with ribs
radiating from the keystone of the apsidal arch, a rib is occasionally
added in the bay preceding this vault, as for example in Saint
Pierre-le-Guillard at Bourges (fifteenth century vaulting), where this
short rib runs out only to the crown of the six-part vault with which
the last bay of the choir is covered (Plate II-j). Occasionally, too, a
church like the cathedral of Moulins (Allier) (1468-1508), with a ridge
rib the length of the choir, is terminated by a chevet with radiating
ribs which thus receive apparent abutment at their keystone (Plate
II-k).
[Illustration: FIG. 70.--CAEN, SAINT ÉTIENNE.]
A similar purpose of providing apparent abutment would seem to account
for the unusual form of the chevets of Bayeux cathedral (thirteenth
century), and Sant’ Antonio at Padua (after 1232) in which all the
radiants which ordinarily stop at the keystone are carried through
against the face of the apsidal arch. At Bayeux there are two such ribs
(Plate II-l)[386] and at Padua, three (Plate II-m). The latter is also
exceptionally interesting in the form of its chevet which is really a
combination of the diagonal and the buttressing ribbed type.
Although there are occasional instances like the one at Barcelona, in
which the transverse severy of a buttressing ribbed chevet is subdivided
only by a ridge rib, it is far more common to find a more extensive
subdivision of this bay when such subdivision was undertaken at all.
Moreover, it is an interesting fact that many of the elaborated chevet
vaults--for it may be noted here that the apse vault was elaborated just
as were those in the remainder of the church edifice--are fundamentally
based upon the simple chevet with buttressing ribs.
Of these vaults with added ribs, perhaps the simplest are those in which
the western bay is subdivided by the introduction of a ridge rib running
about half way to the crown of the apsidal arch and there met by two
tiercerons rising from the imposts of this same arch (Plate II-n). A
good example appears in the cathedral of Bayonne (Basses-Pyrénées)
(after 1213), and another in that of Saint Quentin (Aisne) (commenced
1257), while the same subdivision of this severy in combination with
other subdivided cells is to be seen in the Marien-kirche at Stargarde
(Germany) (fourteenth century) (Plate IV-d).
A second and unusual division of this severy appears in the cathedral of
Saint Jean at Perpignan (Pyrénées-Orientales) (1324-1509),[387] where
the customary three-part bay containing the buttressing ribs also
contains two diagonals precisely like those in a four-part vault (Plate
II-o). A similar arrangement, with the addition of a ridge rib (Plate
II-p), may be seen in the church of Saint Jean at Ambert (Puy-de-Dôme)
(fifteenth and sixteenth centuries). Such subdivisions as these last two
quite evidently had for their object not merely a reduction in the size
of the spaces to be vaulted but also an effort to retain the
buttressing-ribbed type of chevet and still obtain a window cell which
would not have the warped surface characteristic of this form.
[Illustration: FIG. 71.--CHALONS-SUR-MARNE (NEAR), NOTRE
DAME-DE-L’ÉPINE.]
A still more elaborate subdivision of the rectangular vaulting bay
appears in the chevet of Notre Dame-de-l’Épine near Chalons-sur-Marne
(1419-1459) (Fig. 71), where this bay contains no diagonals at all but
is divided by a series of tiercerons and short ridge ribs in a manner
best understood from the plan (Plate II-q). But it is the subdivision of
the window cells of the apse proper which is of especial interest at
l’Épine, for the method here employed was very widely extended in the
later Gothic period. It consists in the introduction into each of these
cells of a short ridge rib running from the central keystone to a point
about half way to the window crowns where it is met by two tiercerons
which rise from the impost of the principal ribs of the chevet on either
side of the window. The apparent object of the system is to so subdivide
the vault surface as to break up its compound or ploughshare curves and
substitute smaller panels whose surfaces are simpler to construct
exactly as in the similar nave vaults previously described. This purpose
does not show to advantage at l’Épine, where the awkward adjustment
between the vault panels and the window heads would seem to indicate
that the apse was originally designed for a simple form of chevet with
no added ribs. Better examples could be cited, among them Saint Severin
at Paris. Such an arrangement of window cells as that in these vaults
practically converts the chevet into a ribbed half dome pierced with
lunettes which do not rise to its crown. This may clearly be seen from a
study of the apse of Saint Jacques at Antwerp (probably sixteenth
century), where the vault is unusual in the omission of all the true
radiating ribs (Plate II-r). As a matter of fact such ribs were no
longer of value since they did not mark the intersection of two vault
panels but merely lay along a surface which is almost precisely like a
section of a half dome. The tiercerons are still important since they
mark the intersection of the window lunettes and carry the weight of the
vault down to the piers. They are therefore retained. Thus, while the
absence of radiants in Saint Jacques might seem to make this vault
structurally less correct than that of l’Épine in reality such is not
the case.
Once it became the custom to introduce extra ribs into the chevet, this
portion of the church underwent the same treatment as the vault of the
nave or choir. Thus in England, to cite only extreme cases of
elaboration, the later Gothic produced such vaults as those of
Tewkesbury Abbey (between 1325 and 1350),[388] in France, such pendant
types as that of Saint Pierre at Caen (probably early sixteenth
century), and in Germany such a choir and apse as that of Freiburg
cathedral (late fifteenth century) (Fig. 72).[389] The last named is
especially interesting as showing the low point reached in rib vaulting
for its ribs have almost no function as supporting members, some of them
being actually free from the vault panels and are merely used to form a
decorative pattern upon a vault which would stand equally well were they
entirely removed. Such chevets are, in many cases, clever examples of
stone cutting and decorative design but they are lacking in fundamental
structural character.
THE NUMBER OF CHEVET CELLS
[Illustration: FIG. 72.--FREIBURG, CATHEDRAL.]
Thus far the discussion of chevets has been distinctly from a structural
point of view, but there remain certain other differences between these
vaults which are worthy of remark. In the first place, there is the
matter of the number of cells comprised in the chevet. The standard
during the best Gothic period was seven, though five was a frequent
number and quite often nine are found (Plate II-s), as for example, in
the apse of San Francesco at Bologna, Saint Martin at Ypres, Belgium,
and that of Béziers (Hérault), cathedral (1215-1300).[390] In the
smaller churches and in the radiating chapels there are frequently
three. Moreover, when the apse has a central pier,[391] there are an
even number of bays and thus four and six-celled chevets are employed.
That in Saint Pierre at Caen, for example, has four bays all on the
curve, and that in Notre Dame at Caudebec-en-Caux (Seine-Inférieure)
(fifteenth and sixteenth centuries) (Plate II-t) has only two bays thus
placed, a fact which gives an angular character to the apse which is far
from pleasing.[392] As for the chevets with six cells, they are of very
infrequent occurrence, though one is to be seen in Saint Pierre at
Auxerre (Plate II-u). A chevet with the unusual number of eleven cells
is to be seen in the church of La Chapelle-sur-Crécy (thirteenth
century).[393] In construction, this chevet is similar to one bay of
such an eight-part vault as that at Provins, Saint Quiriace[394] with
its easternmost cell divided into five parts.
THE USE OF A CENTRAL PIER IN THE APSE
An interesting question arises in this connection as to why the central
pier was employed in the mediaeval church. It is not common, yet it
occurs frequently enough and over a sufficient space of time to prove
that it did not lack a certain amount of popularity. Thus an apse with
such a pier is to be seen in the early Romanesque church of Vignory
(Haute-Marne) (consecrated cir. 1050-1052), where it is covered by a
half dome, and again at Morienval (Oise) (Fig. 77), where there are ribs
beneath a similar vault.[395] Throughout the Gothic period, this plan of
apse surmounted by a chevet occurs in an even larger number of examples
and toward the close of the period becomes quite popular. Leaving out of
consideration the origin of the employment of a central eastern pier,
which would seem most difficult to ascertain, it is at least interesting
to note the effect which a chevet with a central rib presents when
compared with the more usual type. If, for example, the apse of Saint
Pierre at Auxerre be compared with that of the cathedral of Reims, the
advantage and disadvantage of the two methods from the point of view of
appearance may be seen. The most displeasing feature of the apse of
Reims lies in the fact that its central arch and window, being seen in
their full width, seem disproportionately wide in comparison with those
on either side, while at Auxerre there is no window shown in its full
width with the result that the transition is apparently more gradual
from the ends to the center of the apse. On the other hand, the apse of
Reims permits the addition of a lady chapel with an arch on the major
axis of the church.[396] Altogether it is largely a question of personal
preference which would seem to have guided the builders, combined,
perhaps, with some considerations based upon the size of the apsidal
curve and as to how many divisions would give the most pleasing form to
the apsidal arches. As far as the actual construction of the chevet is
concerned, the plan with a central pier made no essential difference,
except possibly in the vaulting of the ambulatory which is discussed in
the next chapter.
IMPOST LEVELS OF CHEVET VAULT RIBS
Another interesting, though minor feature of chevet vaulting, lies in
the form of the masonry panels and the position of the imposts of the
radiating ribs. The position of the latter varies considerably, though
it corresponds in general with the impost level of the transverse arches
in the nave or choir of the church. In the best period this was
generally somewhat above the sill line of the clerestory windows, but in
some of the early churches like Saint Germer (Fig. 63), Saint Quiriace
at Provins (Fig. 31), and the cathedral of Bourges (Fig. 76), it is
below this line, while in a number of later churches, among them Saint
Urbain at Troyes (Aube) (1262-1329) (Fig. 73), it is as high as that of
the arches forming the window heads. This last chevet is also important
as showing a tendency to do away with the flat wall forming the lower
portion of each panel and starting the outward curve of the masonry
directly from the extrados of the ribs. Although this detracts somewhat
from the beauty of the vault by making the curve of its cells too
abrupt, it does prevent large portions of the windows from being
concealed and therefore gives a more uniform effect to the
clerestory.[397] Such an arrangement of the window cells is to be found
even earlier in the chevet of Bayeux cathedral (early thirteenth
century), where the rib rises from the clerestory string-course but is
kept close against the wall to the impost of the window arches so that
the effect produced is much like that at Saint Urbain.
THE SHAPE OF THE CHEVET CELLS
[Illustration: FIG. 73.--TROYES, SAINT URBAIN.]
Another feature of chevet vaulting which varies greatly throughout its
history, is the comparative height of the crown of the wall rib, or line
of intersection, and that of the main keystone; in other words, of the
doming up of the vault panels. In this, there is a very wide divergence
all through the Transitional and Gothic periods. Thus among the early
chevets it will be noted that in some the doming is slight though
noticeable, as at Saint Germer (Fig. 63), in others it is very
pronounced, as at Vézelay (Fig. 66), while in others the crown of the
cells actually curves downward toward the central keystone. This is an
exceptional type, of which there is an example in Saint Remi at Reims
(Fig. 64). Naturally enough, the
[Illustration: FIG. 74.--ANGERS, CATHEDRAL.]
vault which is most highly domed up exerts the least outward thrust and
is thus most easily supported. It is not surprising, therefore, to find
this form a favorite where large windows were not required in the apse
or where there was no ambulatory or but a low one. This may perhaps
explain its use in the south of France in the cathedral of Béziers
(Hérault), as well as its popularity throughout Italy, where it may be
seen on an exceptionally large scale in the cathedral of Milan. Certain
of these domed up chevets may also be attributed to the type of nave
vault developed in the locality in which they are found, as, for
example, the chevet of Angers cathedral (Fig. 74), which is very highly
domed, with the small torus ribs of the region forming the radiants
beneath it. As a matter of fact, such a chevet as this differs from a
ribbed-lobed-dome only in having its masonry courses running at right
angles to the supporting walls. Its pressures are almost all downward
with but little outward thrust though the arrangement of the masonry
courses and the shape of the vault cells serves to concentrate both
thrusts and pressures upon the ribs and piers instead of along the whole
curve of the outer walls, thus rendering perfectly safe the introduction
of large windows.[398]
CHEVETS WITH PIERCED PANELS
[Illustration: FIG. 75.--AUXERRE, CATHEDRAL.]
Still another interesting characteristic of certain chevet vaults is the
presence of openings from one cell to the next in the lower portion of
the panels between them. The simplest of these are to be seen in the
cathedral of Auxerre (choir finished 1234) (Fig. 75), and it seems very
reasonable from their square shape, comparatively small size, and their
position at the beginning of the curve of the vault cells to assume that
they were intended to hold wooden beams, used, quite possibly, as
supports for scaffolding or centering for the rest of the vault.
Whatever their use, they may be the prototypes of such larger openings
as those in the cathedral of Bourges (after 1215) (Fig. 76), which may
not only have been used in a similar manner but which, from their
circular shape and moulded character, supply a certain amount of
decoration to this part of the vault and even serve in a slight degree
to distribute the light from its windows over a larger area.[399] An
even greater amount of decoration is obtained by the use of tracery in
the similar openings in the cathedral of Orleans (begun 1630), which are
of larger size and of a generally triangular shape.[400] The final
development of such tracery panels may be seen in the Brunnenkapelle of
Magdeburg cathedral (fourteenth century)[401] where the apse vault
proper becomes practically a flat ceiling the entire space between it
and each of the ribs being filled with tracery.
[Illustration: FIG. 76.--BOURGES, CATHEDRAL.]