Square Nave and Rectangular Aisle Bays

Fig. 21.—Angers, Saint Serge.

Besides its use in Lombardy and Anjou, the square nave bay with four part cross-ribbed vaults, was employed to some extent in other parts of Europe throughout the Gothic period.[168]Some of these are churches without side aisles, but aisles are more commonly found, divided into rectangular bays corresponding in number to those of the nave. Of the single naved churches, San Francesco at Assisi,[169]is a good example. Although dating from 1236-1259, its vault ribs are still heavy and almost square in section, as if derived from Lombard prototypes. But they differ in being of pointed section and in not giving to the vaults a domed up crown. In this they would seem to be examples of French influence upon Lombard tradition.

An early church with square nave bays and ribbed vaults over rectangular bays in the side aisles (Plate I-b.), is to be found at Bury (Oise) (Fig.

Fig. 22.—Bury, Church.

22). It probably dates from about 1125, and is an important monument of the Transitional period. Its nave vaults are quite highly domed and in this respect seem somewhat Lombard, but their pointed arches and awkward construction indicate an effort on the part of the builders toward reducing this doming and a dawning consciousness of the value of the pointed arch in the construction of ribbed vaults. This is further shown in the side aisles. Because of the rectangular shape of the bays, the problem was presented of getting three sets of ribs of different span to rise to the same or practically the same height. Not being thoroughly familiar with the flexibility of the pointed rib, the builders at Bury were naturally somewhat clumsy in its use. Thus, the diagonals were made segmental in elevation to lower them to the level of the pier arches, whilemasonry was piled on the crown of the transverse ribs, or their voussoirs widened, to bring them up to the level of the vault panel.[170]A few such experimental steps as these at Bury, were all that were necessary to give the builders a mastery of the use of the pointed arch in ribbed vaulting.

Fig. 23.—Bury, Church.

But there is another feature of the side aisle vaults which is worthy of note before turning to the more developed churches which resemble Bury in their arrangement of vaulting bays. This is the use of small caryatid figures which appear at the springing of the diagonal ribs(Fig. 23).[171]These would seem to serve a purely decorative purpose, perhaps to distract attention from the great size of the ribs behind them, or to give anapparent lightness to the vault itself by seemingly placing its burden upon such insignificant shoulders, or more probably still, the figures served to break the transition from shaft to rib by concealing the impost of the latter. Whatever their explanation, other examples besides those at Bury are to be seen. Of these, the angels—now badly mutilated—at the base of the ribs in the narthex of Saint Ours at Loches (Indre-et-Loire)(Fig. 24)[172]are especially interesting, and perhaps account for the tiny figures employed at the springing of the ridge ribs in a number of churches in Anjou, such as Angers, Saint Serge(Fig. 21), as well as for the larger figures in the apse of Notre Dame-de-la-Couture at Le Mans(Fig. 20).[173]It may even be through the influence of such figures as these that grotesques were used to support the small shafts in the arcade of the triforium passage in the cathedral of Nevers (Nièvre)(Fig. 25).

Fig. 24.—Loches, Saint Ours.

Fig. 25.—Nevers, Cathedral.

Returning to the churches later in date than Bury but vaulted on the same plan, it will be found that there are but few examples in France, an interesting fact for which an explanation will later be attempted.[174]The lower story of the Sainte Chapelle at Paris (cir. 1250) furnishes one of the rare examples, but here the nave and aisles are of the same height and so do not exactly resemble the system at Bury. Because of their narrowness, the side aisle vaults of the Sainte Chapelle did not furnish proper abutment for those of the nave, and the builders found it necessary to add tie-rods and even transverse half arches forming veritable interiorflying buttresses at about half the height of the transverse ribs. This is, however, a most unusual arrangement.

It was in Italy more than elsewhere that the method of square nave and rectangular aisle bays was adopted. Many of the largest churches of the Gothic period in that country were thus constructed. Among these, Santa Maria Novella at Florence (end of the thirteenth and beginning of the fourteenth centuries) has nave bays which are practically square, while the cathedral of Santa Maria del Fiore (fourteenth century) in the same city is a much larger church more strictly following the type.[175]This vast edifice presented such a vaulting problem that the builders did not hesitate to resort to the use of iron tie-rods to counteract the thrusts,—a subterfuge common enough in Italian architecture, of which the church of the Frari at Venice (after 1250) presents an exaggerated example.

Several factors enter into the lack of popularity of the vaulting system just described especially in the more northern countries, but the fundamental one would seem to be the difficulty of properly lighting churches thus covered. If an examination be made of the churches with a single broad nave and no aisles it will be seen that in Italy, where a comparatively small proportion of window space was necessary, the builders were content with a single window in each nave bay as for example, in San Francesco at Assisi. In France, on the other hand, the light thus admitted would have proved inadequate, and in such churches as the cathedral of Angers(Fig. 19)and Sainte Radegonde at Poitiers two windows were introduced under each wall rib. This is, however, an awkward arrangement because these windows do not properly fill the wall space, and though this is better accomplished by adding a circular window above the upright pair as was done in La Couture at Le Mans(Fig. 20), still the effect even then is not satisfactory and much solid wall which might be utilized for windows is wasted. Moreover, in a church with side aisles, the clerestory arrangement was still more troublesome since important structural difficulties were involved. To raise a great four part vault high above the aisles in order to obtain a largeclerestory was no easy task because of the excessive thrust which such a vault exercised at its four points of support. In Italy, where the amount of light required was not great, a very low clerestory with small, circular windows, one to each bay, was all that was essential, and so in such churches as Santa Maria Novella and the cathedral at Florence the nave vault was placed at a point only slightly above the vaults of the aisles, and its thrusts offset by simple ramping walls beneath the side aisle roofs. Such a church in France would have been inadequately lighted, and even if a greater structural skill permitted the French to erect loftier clerestories than those in Italy, there remained the difficulty of arranging the windows to get the maximum of light and the best appearance. A single opening occupying the entire space beneath the wall rib would have been all head and no jamb. One upright window would have admitted too little light for a large nave, and two windows near together not only left a great deal of wall space unused but were most awkwardly placed in churches where one nave bay corresponded to two bays in the aisles as in Le Mans cathedral,[176]because they were not on an axis with the arches of the nave arcade. On the other hand, if placed on this axis, the resulting windows were necessarily of small size like those in such Rhenish churches as the cathedral of Speyer where a second stage of windows has been added one in the center above each lower pair in a far from satisfactory manner since it brings a window above the intermediate pier.

In view of these facts it is at least a reasonable assumption that the lighting problem had much to do with the discarding by the French builders of the simple square four-part nave vault. As a matter of fact, however, they did not exactly discard it, but evolved from it a vault in six cells, which, while it still retained the old division of the nave into square bays, each corresponding to two bays in the aisle, at the same time permitted the uniform treatment of these in elevation and made possible larger windows,—one to each aisle bay,—symmetrically placed and, in the course of time filling the entire space beneath the wall ribs. This six-part ribbed vaulting would seem to have originated early in the twelfth century, in the French province of Normandy. This province has already been mentioned as the center of a Romanesque school, which extended over the greater part of England after the conquest of 1066, and reached its height during the reign of Duke William, the Conqueror (1035-1087), when a vast number of churches were constructed, many of them of large size. These were in general wooden roofed throughout, though, occasionally, as has been shown,[177]groined vaults were used in the choir or aisles, or both. Toward the beginning of the twelfth century, however, the Norman builders determined to vault the naves of a number of these churches, among them the two abbeys at Caen, and the result of this determination was the evolution of the true and false six-part vault.

Like the Rhine provinces, Normandy had always been strongly influenced by the methods of building developed in Lombardy. Whether this was due to the presence in Normandy of such men as Lanfranc,—who was born in Pavia in 1005 and became successively prior of Bec (1045-1066), abbot of Saint Étienne at Caen (1066), and archbishop of Canterbury (1070-1089), and who may have kept Normandy closely in touch with Lombardy,—or whether there were other more powerful influences, it is impossible to state, but in any event the architectural analogies between the two schools are striking. This is especially true of the type of shafted pier most frequently found in Normandy, and of the alternate system of light and heavy supports, which, while it does not characterize all the churches of the school, is found in many of them. Thus when the Norman builders determined to vault their great churches at Caen, one would naturally expect to find them turning to Lombardy for a method of vault construction, especially since Sant’ Ambrogio at Milan had been successfully completed at least a quarter of a century before their determination was made. And in fact this is probably what they did. But there were certain differences in structure between the churches of the two schools which made it impossible for the Norman builders to adopt unchanged, the heavy square, domed-up, cross-ribbed vaults of Lombardy. The first of these differences lay in the fact that the Norman churches were originally built for wooden roofs,—which may even have been in place, in many cases, when the vaults were begun,—while the Lombard churches were planned from the ground for their vaulting. Thesecond difference was, that the Norman interior system possessed a clerestory window of considerable size centered above each of the arches opening into the side aisles,—that is two in each wall of what would be a square nave bay,—while the Lombard churches either had no clerestory at all, as at Sant’ Ambrogio, or one in which the windows were small and there was no attempt to center them as in San Michele at Pavia.

It was natural that the Norman builders should have preferred to preserve their interior and exterior elevations as nearly as possible as they were when only a wooden roof was used, both to avoid the expense which would be involved in reconstruction and to preserve the large clerestory so essential in a northern country. To vault these churches and at the same time save this clerestory would seem to have been the problem, therefore, which the builders set themselves to solve. That they attempted to use the four-part vault in its solution will be seen from an examination of the seven vaulted churches[178]still remaining in which the old system of square nave bays is found, for in four of these a variant of four-part ribbed vaulting was employed while in the other three a new method was developed out of the four-part type.

A study of the two abbeys at Caen will illustrate this. Of the two, Saint Étienne or the Abbaye-aux-Hommes (cir. 1064-1066) would seem to be the earlier as far as its vaulting is concerned and this would seem to date from about 1135. In its nave(Fig. 26)the alternate system of supports is employed, though all the piers are of almost the same section with a single shaft carried up the inner face. The aisles are in two stories and there is a clerestory with a single window in each bay. The nave was originally covered with a wooden roof. With this elevation existing before the church was vaulted it is quite possible to account for the form which this vaulting assumed. The first step must have been to divide the nave into square bays by transverse arches,—assuming that these were not already in place. The springing of these arches must naturally have been governed by that of those which opened into the crossing, and the level of their crowns, by the wooden timbering of the roofs,—which may well have been in place when the vaults were built. The result was that these transverse arches had to rise from a point as low as the clerestory string-course and could only be a slightly stilted semicircle in elevation. If the

Fig. 26.—Caen, Saint Étienne.

bays thus constituted were to be covered by four-part vaults of Lombard type, the next step would have been to erect diagonals of semicircular section thus doming up the vault at the crown, but at Caen such diagonals would have rendered necessary an entire change in the timbering of the roof because their intersection would have risen above the level of the trusses. Hence segmental diagonals were substituted. Upon this skeleton of ribs, it would have been quite possible to place a four-part vault, but the wall intersection of its panels would have cut off the heads of the clerestory windows. Several methods could have been used to avoid this. In the first place the severies could have been so shaped as to cut the walls in a curve above the window, but this would have given a flattened form to the panel and rendered it most difficult both to construct and to support when in place. A second expedient would have been to reduce the size of the windows but this, besides cutting off most necessary light would have utterly destroyed the splendid proportions between the horizontal divisionsof the Norman interior. A third method would have been to move the windows toward the intermediate pier, but this would have destroyed the axis line of the aisle, triforium, and window arches, and was wisely rejected. Lastly the imposts of the ribs could have been raised, but even this would have introduced enormous structural changes: first, because it would have rendered necessary a change in the timbering, or else raising the entire roof of the church; second, because it would have placed the new impost out of level with the crossing arches; third, because it would have greatly increased the thrust of the vault, already most difficult to meet because of the segmental form of the diagonals and the lack of extensive knowledge of buttressing principles on the part of the Norman builders.

To avoid all these difficulties and still retain the windows, a new method of vaulting was evolved. An intermediate transverse arch was added meeting the diagonals at their intersection, and above the triangular window cells thus formed, separate vault panels were constructed(Fig. 26). The line of the window heads was thus left undisturbed and the six-part vault created (Plate I-c.).

Of course, the foregoing suggestion that the six-part vault was evolved from four-part vaulting is largely conjectural, but an examination of other churches in Normandy would seem to show that the Norman builders almost always preferred to use the simple four-part vault in a slightly modified form whenever it was possible to do so and still retain the clerestory windows, rather than to employ the developed six-part type. This modified four-part vault may properly be termed false or pseudo-sex-partite. That it was not a mere prototype of the more developed six-part form would seem to be shown by the fact that it was built in churches both contemporary with, and subsequent to those with true six-part vaults.

A good example of pseudo-sexpartite vaulting, for comparison with that of Saint Étienne(Fig. 26), is afforded by La Trinité or the Abbaye-aux-Dames at Caen(Fig. 27). It would seem probable that the upper portions of this church were extensively rebuilt at the time when vaulting was added. In this rebuilding, concealed flying-buttresses were constructed beneath the side-aisle roofs, and these, together with the solid wall which

Fig. 27.—Caen, La Trinité.

replaces the open triforium gallery of Saint Étienne, made it possible to raise the level of the transverse arches of the vaulting to a point considerably above the clerestory string-course. Furthermore, since the wooden outer roof was probably built after the vaults, it was possible to use diagonals whose crowns were higher than those of the transverse arches, and still place them beneath the roof trusses. With such a skeleton of ribs as a basis, the builders proceeded to erect a four-part vault over each nave bay, or, in other words, enclosing two side aisle arches. Because of the higher impost of the vault ribs, the wall intersection of the vault cells easily cleared the window heads.[179]Curiously enough, however, the builders connected the intermediate piers with a transverse archhaving a flat wall built upon it to the level of the crown of the longitudinal vault cells(Fig. 27). There would seem to be several explanations of this innovation. In the first place the pier system of La Trinité is regular, not alternate, and a greater symmetry was obtained by having corresponding transverse arches connecting each pair of opposite piers. Moreover such arches had been used before 1114 in the church of Saint Georges at Boscherville, and quite possibly elsewhere as well,[180]beneath a simple wooden roof, thus tying together the lofty clerestory walls. In the second place, such arches had already been introduced at Saint Étienne, though for a different reason, as has been shown, and must have proved of value in keeping the keystone of the diagonals rigidly fixed, besides having become a characteristic of what was perhaps the major church of the school; and in the third place, such an arch with its wall above aided materially both in carrying a portion of the weight of the vault to the alternate piers and in affording permanent centering, which was needed in Normandy even more than in Lombardy because the Norman vault crown was never more than slightly domed up.

Once introduced, this pseudo-sexpartite vault was not restricted to La Trinité but was, as has been said, employed in no less than four of the seven square-bayed Norman churches. At Ouistreham (Calvados)[181](vaulted cir. 1160), the impost was raised as in La Trinité and pointed transverse arches were used, thus increasing the curve of the diagonals and improving the stability of the vault. More interesting still, however, are the two churches of Bernières-sur-Mer,[182]and Saint Gabriel (Calvados)[183](both vaulted cir. 1150), for in them the builders have clung so tenaciously to the pseudo form in preference to the true that they have actually moved the windows of each bay toward the intermediate pier in order to use this method without raising the imposts. The latter is particularly interesting because of the extreme flatness of its diagonals for which the intermediate transverse arches must certainly have proved an added support.

The preference of the Norman builders for this pseudo-sexpartite vault, even to the extent of moving the windows out of center to make its use possible, may find a further explanation than any yet given in the simplicity of its construction. A comparison of one window severy of Saint Étienne(Fig. 26)with one at La Trinité(Fig. 27)will illustrate this point. In the former the surface of the vault is warped on either side of the window, while in the latter, the stone courses run almost directly back to the wall, so that the line of intersection is approximately the projection of one-half of the diagonal rib. Of course this second surface was far easier to calculate geometrically and could be put in place by less skillful builders than the warped surface required. It had, however, the fault of being in ill accord with the curve of the window head, but, on the other hand, it possessed the structural advantage of distributing the thrust of the vault over a large amount of exterior wall. This might seem a fault rather than an advantage, were it not that in such a primitive system as that of Normandy, thickness of wall was the greatest factor in abutment and thrusts which were widely distributed were thus more easily met than those which were concentrated within narrow perpendicular limits.[184]The advantage of the warped system in thus concentrating the thrusts was, in fact, realized only when inert stability which forms the keynote of Norman work gave way to the carefully balanced thrusts and counter-thrusts of Gothic architecture.

The little church of Le Petit Quévilly (Seine-Inférieure)[185](cir. 1156) would seem at first to disprove this Norman preference for pseudo-sexpartite vaults. The imposts of its arches are sufficiently high to permit of such a type, yet the real six-part vault was employed. The explanation of this would seem to lie in the geographical situation of the church, for it is not in Calvados, like the other examples, but in Seine Inférieure near Rouen, or in other words on the border of the Ile-de-France, where the six-part vault had been adopted with enthusiasm and used as early as 1140,or some fifteen years previous to the building of Petit-Quévilly, in the large abbey church of Saint Denis.

It is also difficult to explain the use of the true form in the seventh of the vaulted churches, which is that of Creully (Calvados),[186]but the fact that it has the same low imposts as Saint Étienne at Caen combined with the evident purpose of the builders to keep the windows in the center of the bays may perhaps furnish an explanation of its appearance here.

The true six-part vault, as used in Saint Étienne, was far from being perfect. In the first place, it possessed a number of inherent structural faults. These lie chiefly in the unequal distribution of thrusts, and the unequal size of the panels into which the vault is divided. From an aesthetic point of view, two other faults might be added: first, the decrease in the apparent length of the nave, due to the fact that it was divided into a few large bays, instead of twice as many smaller ones; and second, the fact that the crowns of the vault cells above the windows do not run out perpendicularly from the clerestory wall but at an awkward angle, thus greatly injuring the symmetry of the bays. Yet in spite of these drawbacks, which were common to all six-part vaulting, this system had a long period of popularity. There are, however, certain structural weaknesses in these early Norman vaults which were largely due to lack of experience on the part of the builders, and not to the form of the vaults themselves. Wall ribs were, for example, omitted, and the diagonals were made of segmental section, thus rendering unnecessarily severe the thrusts of the vaults. Moreover, such a church as St. Étienne was not planned from the ground for vaulting and the piers had not the proper arrangement of shafts. Last of all, the intermediate arches were of a rather ugly, stilted character, possibly so constructed with an eye to a better distribution of light, but in any event presenting an awkward appearance. All these faults were gradually overcome in the Transitional and Early Gothic churches of the Ile-de-France.

That it should have been this province which favored the six-part system is most curious, for at a date almost contemporary with St. Étienne atCaen, ribbed vaults of rectangular plan had probably been constructed over the naves of Saint Étienne at Beauvais and the abbey church at Saint Germer-de-Fly (Oise) (cir. 1130-40). That this method was abandoned in most of the remaining Transitional churches would seem to have been due to the fact that the vaults of Saint Étienne at Beauvais fell in, and those of Saint Germer did not prove very secure.[187]Such builders as the Abbot Suger of Saint Denis, therefore, may very naturally have looked to Normandy for a method of vaulting, since the vaults of Saint Étienne at Caen had at least remained in place.

Whatever the cause of its introduction into the Ile-de-France may have been, the six-part system was used at Saint Denis (Seine) (1140-1144) and soon became the favorite method throughout the neighboring region. Unfortunately Saint Denis and two other important churches of the Transition, the cathedrals of Senlis (Oise) (cir. 1150) and Noyon (Oise) (cir. 1140), which would undoubtedly have illustrated the progress in six-part vaulting, no longer have their original vaults, and the cathedral of Sens (Yonne) (1140-1168)(Fig. 28)remains as perhaps the most important example of the early developed type.[188]Its vaults show the great advance made in construction since the completion of Saint Étienne at Caen. The diagonals are semicircular instead of segmental arches, and the transverse ribs are pointed and all of similar curve, giving a more symmetrical appearance and greatly reducing the thrusts. Furthermore the piers are profiled from the ground according to the load which they are to carry, and, last of all, a highly stilted wall rib is added over each clerestory window, completing the skeleton of the vault and making possible a larger expanse of glass and more satisfactory illumination for the interior. Of course, the use of the flying buttress, which had been introduced a short time before Sens was built, contributed enormously to the advancement of vault construction and in large measure explains such an improved form of vaulting as this is. In fact, a heavy clerestory wall was no longer essential to the support of the vault and it was only the fact that a large expanse of glass was not safe from the pressure of the wind, which prevented the clerestory windows from occupying the entire

Fig. 28.—Sens, Cathedral.

space beneath the formeret. With the invention of tracery, what little wall remained, was to disappear. A further advance is shown in the decidedly stilted form of the wall ribs, which(Fig. 28)concentrate all the thrust of the vault upon a very narrow strip of exterior wall where it was admirably met by the flying-buttress.[189]In fact, the system at Sens might be considered perfected were it not for the unnecessary size of the ribs, especially those running transversely. It remained for the builders of the cathedral of Notre Dame at Paris (begun 1163) to reduce all the ribs to the same size, and for the builders of the cathedral of Bourges (Cher) (begun 1172), still further to reduce all but the transverse arches and to employ the vault upon a scale even greater than that of Paris. In fact, Bourges marks the high water mark of this system of vaulting and by the beginning of the thirteenth century it was in general, entirely givenup[190]in favor of the four-part cross-ribbed vault of rectangular plan, which regained its supremacy in the Ile-de-France after the introduction of the flying-buttress with the protection which this afforded against such a catastrophe as that which probably befell Saint Étienne at Beauvais.

Although employed to a much greater extent in France[191]than elsewhere, almost every country in Europe possesses a number of churches with six-part vaults. Thus William of Sens introduced the system into England, where it appears in Canterbury cathedral choir (1175) and later in Lincoln transept[192](cir. 1215). Italy possesses many examples, among them the large churches of San Francesco at Bologna (cir. 1240), the Certosa of Pavia (1396), and the small church of Corneto-Tarquinia (Roma)[193]where the vault curiously enough appears over two bays of rectangular plan which divide what would otherwise be practically a single square nave bay.[194]Examples in other countries might be cited, but in no case would they differ materially from the French prototypes.

The fact that six-part vaulting declined rapidly in favor toward the beginning of the thirteenth century, and thus before the era of complicated vaults had begun, probably explains the few variants from the standard type. Of these, the simplest consists in the addition of a ridge rib along the longitudinal vault crown. This appears in one bay of the choir of Lincoln cathedral[195](Fig. 35), where the crown line is horizontal, and in the great transept of the same church where it rises and falls in accordance with the doming up of the central keystone. The small church of Saint Jacques at Reims (Marne) (1183)(Fig. 29)presents a still better example of this irregular ridge rib. The vault of Saint Jacques would seem from its general appearance to be based upon Anjou models and it is notsurprising to find its possible prototype in the church of La Trinité at Angers(Fig. 30). The reason for the employment of the extra rib is probably twofold: first, to lessen the size of the transverse panels; and second, to render the arrangement of the ribs and severies more symmetrical. In England, it is quite possible that it served as a cover-joint as well, but in France this would not seem to hold true, at least in La Trinité, where the stone courses are laid with as much care as those in the simple four-part vaults of Angers cathedral(see Fig. 19).

Fig. 29.—Reims, Saint Jacques.

La Trinité at Angers(Fig. 30)is also an important variant of the six-part vault because the impost of its intermediate rib is raised to a considerably higher level than that of the principal transverse arches and the intermediate rib itself is highly stilted. This would seem further evidence that the six-part vault was evolved from the four-part vault in an effort to make the arrangement of the windows more symmetrical in a single nave bay corresponding to two bays in the aisles;[196]for if LaTrinité with its series of side chapels, two to each nave bay, had been vaulted in the usual Anjou style and the windows left as they now stand on the axis of each chapel arch, their heads would either have been cut by the wall line of a four-part vault or would have appeared awkwardly placed beneath it. The addition of an intermediate transverse arch and the conversion of the vault into sexpartite form restored the symmetry of piers, arches, and windows. In order, however, to obtain as much light as possible and to produce the effect of square nave bays, these intermediate transverse ribs were stilted and their imposts raised. Nor was this stilting confined to Anjou. It appears a number of times elsewhere often in churches where the ridge rib was not employed for example, in the cathedrals of Bremen and Limburg[197]in Germany, and in those of Ribe,[198]and Viborg in Denmark.[199]

Fig. 30.—Angers, La Trinité.

The church of the Certosa of Pavia in Italy (1396) has six-part vaults of similar type but presents a curious arrangement of square nave bays corresponding to rectangular bays in the side aisles (Plate I-d.).[200]The intermediate transverse arches, therefore, rise from corbels above the crowns of the side aisle arches, a fact which explains their higher imposts. Why such a vault should have been used can again be explained by the desire to obtain the best possible arrangement of windows. Five-part vaults had already been used in the aisles of the Certosa to get square flanking chapels, and it was natural that the builders should have wished to have a clerestory window corresponding to each exterior bay of the church. The fact that square nave and rectangular aisle bays were used at all would seem to have been due to the Italian fondness for this system which caused the least possible obstruction of the church interior by piers. The only curious feature is, therefore, the use of the six-part, instead of the more natural four-part, vault.

A somewhat similar arrangement with the substitution of two four-part vaults for the six-part vaults of Pavia is to be seen in the cathedral of Magdeburg,[201]where the same combination of nave and aisle bays occurs. The builders, like those of Pavia, first subdivided the outer longitudinal cells of the side aisle vaults by a half rib in order to obtain two windows instead of one, which would necessarily be of rather clumsy shape or of small size were it placed below the long, low wall rib of a simple rectangular four-part vault. Then to make the nave bays and clerestory windows correspond to those of the aisles in exterior elevation, as well as to obtain better window space, they constructed two rectangular four-part vaults over each square nave bay with their intermediate transverse rib resting on corbels above the aisle arches (Plate I-e.).

There is one more important variant of the six-part vault which is especially interesting and unusual. It appears in the church of Saint Quiriace at Provins (Seine-et-Marne) (cir. 1160)(Fig. 31)[202]and

Fig. 31.—Provins, Saint Quiriace.

consists in a division of the nave into great square bays each corresponding, not to two, but to three square bays in the side aisle (Plate I-f.). The divisions thus formed are covered by what is really an eight-part vault, which is precisely like six-part vaulting except that there are three instead of two window cells in either side of each bay. Needless to say the immense size of the transverse triangular severies thus created presented astructural problem of much difficulty, and it is not surprising that such a vault was but seldom imitated,[203]particularly as the great discrepancy in the size of the vault cells and the awkward angles formed by their crowns give a decidedly unpleasant appearance. Nevertheless, there is one instance, at least, in which this system was not only imitated but transformed into a ten-part vault. This was at Boppart, Germany,[204]where the thirteenth century church has vaults with four window cells and but a single pair of diagonals. To break up the two remaining triangular severies, added surface ribs were introduced (Plate I-g.).

While the builders of Normandy were developing the sexpartite system just discussed, those of the Ile-de-France were experimenting with the simple four-part cross-ribbed vault of rectangular plan (Plate I-h.). As in Normandy, the earliest churches of the province were in the main wooden roofed basilicas like the Basse-Oeuvre at Beauvais. When groined vaults first appeared in the Romanesque period, they were generally employed only in the side aisles, as at Morienval,[205]and if one may judge from these vaults, which have unfortunately been rebuilt, they were of slightly domed up section somewhat like those of Lombardy and the Rhenish provinces. Toward the beginning of the twelfth century, however, when the central power had been greatly strengthened under Louis VI. (1108-1137), there began a marked architectural advance which was destined to render this backward province the most important of all in the development of Gothic architecture. One of the earliest churches to mark this advance was Saint Étienne at Beauvais (probably early twelfth century)(Fig. 32), which, if one may judge from the form of the piers and the ribbed vault of the side aisles,[206]was planned from the foundation for vaulting throughout. Unfortunately the original vaults of the nave, if such existed, are no longer in position for they either gave way from lack of support, a natural supposition since they had no other abutment than the weight of the clerestory walls, or else they were so injured by the fire of 1180 that it was necessary to replace them by the existing vaults of the late twelfth century.These, while they do not make up for the loss of their predecessors, are nevertheless important because of their early date. They are antedated, however, by a number of very important churches which still retain, in part at least, their original vaulting.

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