Chapter I: Nave and Aisle Vaults (1)

During the Romanesque period, or roughly speaking, from the beginning of the eleventh to the middle of the twelfth century, three chief forms of vaulting were employed over the naves and aisles of church edifices. The first of these was the dome, the second the tunnel vault, and the third, groined vaulting. With the development of the ribbed vault, all three gave way to this new method of construction, and the Gothic era was inaugurated.

DOMES ON SPHERICAL PENDENTIVES

The dome was employed in two rather distinct ways according to the form of pendentives used for its support. Thus a number of churches continue the tradition of the spherical pendentive, while in others some form of squinch or trumpet arch is found. Both methods are of early origin, dating back, in fact, to the Roman era preceding the reign of Justinian (483-565) and consequently earlier than the Byzantine architecture of which they are so conspicuous a feature. Rivoira[1] has shown the existence of numerous spherical pendentives of the second century A.D. or even earlier, and Lasteyrie[2] has added to these a small cupola at Beurey-Beauguay (Côte-d’Or) in France dating from the second or third century. But even if this method were known at an early date it was not until the Byzantine era that it obtained a wide-spread and extensive usage. During the sixth century it became the principal method of vaulting throughout the Roman Empire, and, as such, had a considerable influence upon Carolingian architecture of the ninth and tenth centuries. This is true even in France, for traces of pendentives were found in 1870 during a restoration of the church of Germigny-des-Prés,[3] a fact of particular interest because it is in France that the principal Romanesque examples of this method are to be seen.

DOMES ON SQUINCHES

As for the squinch, it may possibly be of Persian origin, but the earliest examples thus far known in Persia are to be found in the palaces of Firouz Abad and Sarvistan, which probably date from the Sassanian period between A.D. 226 and 641, and are therefore of later date than the Roman examples of the first and second centuries to be found in the Palace of the Caesars at Rome and the Villa Adriana at Tivoli (cir. A.D. 138). Whatever its origin, the squinch in its various forms, simple cross lintel,[4] cross arch, trumpet arch, niche head, etc., was employed prior to and during the Byzantine period along with the spherical pendentive. In fact a trumpet arch of domed up character is found in the Baptistery of the cathedral of Naples[5] which dates from the fifth century, while the niche head or half dome type, very commonly employed in Romanesque architecture, has a sixth century prototype in the church of San Vitale at Ravenna,[6] as well as many earlier examples such as those in the Domus Augustana (cir. A.D. 83),[7] or the Thermae of Caracalla (212-216)[8] at Rome. Other types of squinches occasionally appear but they are generally referable to one of the above mentioned forms.

THE SCHOOL OF PERIGORD

By far the most important group of Romanesque churches employing the dome on spherical pendentives, is situated in that portion of France extending around the city of Périgueux, and constitutes what is known as the architectural school of Perigord. Since Périgueux was a trading post on the route from Venice to the west, it must have felt a good deal of Byzantine influence, and it is the general theory that to this influence is due the almost universal employment of the dome on pendentives in the churches of this school. While this may well be the case, it is nevertheless to be remarked that the dome as a method of vaulting seems to have been the only importation, its construction in Perigord differing in almost every particular from that of the Byzantine period. This might even seem to indicate that the Perigord type of dome was not imported, but actually indigenous to this part of France, a theory which has lately been advanced by no less an authority than Lasteyrie.[9] But in any case, the points of difference in construction between the domes of Byzantine architecture and those of the school of Perigord are of more importance in this discussion of vaulting, than is the question of their origin.

COMPARISON OF PERIGORD AND BYZANTINE DOMES

These differences have been so admirably summed up by Lasteyrie[10] that a translation of his summary with a few additions will perhaps give the best possible account of them. They are grouped under six chief heads which may all be studied by using the cathedral of Saint Front at Périgueux (Figs. 1 and 2) as a model. First, the French pendentives are borne on pointed instead of semicircular arches; second, the surface of the pendentive at Saint Front rises from the intrados rather than from the extrados of the voussoirs; third, the diagonal profile of the French pendentive is a complex curve[11] instead of a quarter circle; fourth, the oldest French pendentives have their masonry in horizontal courses while the Byzantine frequently have their courses more or less normal to the curve; fifth the springing of the domes of Saint Front is some distance back from the circle formed by the pendentives, the diameter of the dome being thus greater than its impost,[12] while in Byzantine models, the two correspond; and sixth and last, the domes of Saint Front are slightly pointed and, for that matter, all the French domes are at least semicircular, while the Byzantine domes are generally of segmental section. The explanation of all these differences lies in the material employed, for the domes of Perigord are of stone, those of Byzantine architecture are of brick or some other light material. The pointed arch having less thrust than that of semicircular section was better suited for stone construction, a fact which explains the pointed section of many French domes whose outward thrusts were thereby greatly reduced. Moreover, while the light Byzantine material made possible a dome without centering constructed after the manner of the Egyptian “voute-par-tranches,”[13] the heavy stone of the French vault made a centering absolutely necessary, a fact which explains the setting back of the dome from the curve of the pendentives so that the ledge thus formed might serve to support the wooden centering employed.[14] It explains also the horizontal courses since these allowed a greater amount of the weight of each course to be borne by the one beneath it, thus reducing the pressure and making possible a centering of comparative lightness. But these were not the only results of the employment of stone. Since the domes of Perigord are much heavier than the Byzantine domes and exert much more outward thrust it was essential for them to have very firm supports. Perhaps it is with this in view that the churches of this school are for the greater part without side aisles, their outer walls with heavy applied and transverse arches providing suitable support for the domes. Even when aisles exist, they are merely deep wall arches forming transverse tunnel vaults rising from the level of the imposts of the transverse arches of the nave and, with them, furnishing the support for the triangular pendentives. This is the arrangement in the cathedral of Saint Front at Périgueux (Fig. 1), the only church in France of this particular type.[15]

THE EXTERIOR ROOFING OF PERIGORD DOMES

One advantage in the employment of the dome of stone lay in the fact that it might be faced on both the exterior and the interior, or covered directly by tiles without the use of a bonnet of wood and copper, or a roof of wood and tile, so frequently seen in Byzantine work. It is doubtful whether the earliest French domes were treated in this way, however, for indications would seem to point to the original employment of a wooden roof over the domes of the cathedral of Saint Front.[16] Nevertheless, these domes have since been restored with an exterior stone facing (Fig. 2), and a similar treatment is to be seen at Cahors cathedral, and over

the crossing of Angoulême. In these domes the drum is first built up in a slightly ramping wall, to offset the outward thrust of the vault, and the dome itself is crowned by a lantern toward which it has an upward curve, rendering the exterior steep enough to shed water readily. At Angoulême the domes of the nave are entirely concealed by a gable roof, perhaps in the early manner of the school. Still another type of dome covering appears at Saint Étienne in Périgueux,[17] where the curve of the dome does not show on the exterior, but where the drum is first carried up around the haunch, and then surmounted by a flattened conical roof of tile, which rests directly upon the vault beneath.

CHARACTERISTICS OF PERIGORD CHURCHES

It has already been noted that the employment of the dome on pendentives over square bays led to the construction of churches with a broad nave without side aisles. Among the earliest of these are the church of Saint Astier (Dordogne), (founded about 1010 but so mutilated as to show little of its original construction),[18] and Saint Avit-Sénieur (Dordogne) (cir. 1117), originally with three domes which were replaced by domed up Anjou vaults in the thirteenth century.[19] The best of the earlier examples remaining for critical study are, first, the cathedral of Saint Pierre at Angoulême, whose western bay was constructed between 1100-1125,--the remaining three being but slightly later--and second, the church of Saint Étienne at Périgueux, originally with four domes, two of which were destroyed in the religious wars of the sixteenth century. Of the two which remain the more recent must be earlier than 1163, and the other would seem from its appearance to be about contemporary with that of the west bay of Angoulême.[20] These two with the cathedral of Saint Front (after 1120) furnish three excellent examples of the school, to which a large number of other churches might be added as illustrating some minor differences in plan or elevation.[21] The cathedral of Angoulême (Figs. 3 and 4) is characteristic of the school. Deep wall, and heavy transverse arches supply substantial impost for the domes. The piers of the western bay are of simple rectangular plan like those of Saint Avit-Sénieur and Saint Étienne at Périgueux, while those to the east are of a later compound type with transverse arches and wall-arches in two orders instead of the single order of the earlier bay. Except over the crossing, where there is a high circular drum forming a lantern, the domes are not pierced with windows around their base. This is due to the fact that they are covered on the exterior by a wooden roof.[22] It is more usual to find four small windows at the base of each dome as in Périgueux, Saint Front (Fig. 1).[23] The use of stone in the construction of the domes explains the small number of these windows compared to that in Byzantine architecture,[24] since the stability of the vault would be threatened by too many openings. Besides this, the fact that the churches of Perigord have no aisles, properly speaking, permitted sufficient light to enter through windows in the side walls. In fact it seems quite possible that the windows in the domes of the Perigord churches were used to afford resting places for the frame work of the centering even more than for light, a fact which would also seem to be true of the four recesses left in the masonry just above the cornice of the domes of Angoulême cathedral (Fig. 4).

THE CENTERING OF PERIGORD DOMES

In support of this theory it is possible to point out that if long cross beams were used in building these domes, it would be difficult if not impossible to remove them after the dome was finished. If, however, as at Angoulême, small spaces were left in the masonry it would be possible to tilt a beam bevelled at each end and resting on the ledge of the dome and thus remove it without cutting. Still another argument in favor of this theory is the fact that the open spaces to north and south are above the level of the ledge, which would seem to indicate that they were planned to receive the end of a cross beam at right angles to, and above the one running lengthwise. Of course, when windows took the place of these small recesses the removal of the beam could be made through them. There remain, however, a number of churches in which there are neither windows nor recesses, but in most of these the ledge of the dome is itself wide enough to support a beam which could be removed without striking the vault surface.

As for the choirs of the churches of this school, they were occasionally domed as at Saint Front[25] (Fig. 1), but were more often covered by a tunnel vault terminating in the half dome of the apse. The eastern portion of the choir of Saint Front (Fig. 1) and the choir of Angoulême (Fig. 4) illustrate this latter arrangement.

NAVES VAULTED WITH DOMES ON SQUINCHES

Although very frequently used over the crossing of Romanesque churches, the dome on squinches is seldom found over the bays of the nave. There is in fact no distinct school in which this method is employed and the examples of its use are widely scattered. The principal one is, perhaps, the cathedral of Notre Dame at Le Puy (Haute-Loire), which dates from the eleventh and twelfth centuries. Unlike the domed churches of Perigord it is of basilical plan with side aisles. The nave is in six bays with broad arches opening into the aisles and a triforium arcade above them. Across the nave are transverse arches separating the bays. The four toward the east are semicircular, the remaining two are pointed in elevation. These arches rise from imposts nearly or quite as low as those of the nave arcade, and walls are built upon them to the level of the string-course above the triforium. Six rectangular bays,--or seven including the crossing,--of practically square plan are thus formed and each is covered with a dome. In the western bays,--which are at least a century later than those at the east end and therefore more advanced in structure,--a clerestory wall is erected with a single window in its north and south walls, and openings corresponding to windows from one bay to the next above the transverse arches, to secure a good distribution of light (Fig. 5). Across the upper corners of these four walls and rising from the same level as the window heads, are arches with half domed triangular niches beneath them, converting the square into an octagon and furnishing the impost for the domes.[26] These are octagonal in elevation as well as plan and are laid up in flat panels, or gores, which meet at the crown (Fig. 6). It is a type of dome admirably suited to its impost since it presents none of the awkward appearances of a circular dome on an octagonal base.[27] It is also very practical from a structural standpoint. Since the gores are flat, the stone cutting is far less elaborate than in a hemispherical dome, and the gored dome has the further advantage of great flexibility since it may be flattened or raised at the crown, placed over a square bay or one with any number of sides, and made equilateral or with gores of different widths, all with great facility. Furthermore, when the naves are of reasonable width, as in most churches with side aisles, the thrust of the dome is very slight and its downward pressure is not excessive.

But with all its structural advantages, a system like that at Le Puy was not a satisfactory solution of nave vaulting. The transverse arches were necessarily so far below the surface of the dome that the continuity of the nave as a whole was destroyed, and the appearance was rather that of a series of lantern towers or crossings juxtaposed than of a single homogeneous vault.

The side aisles of Le Puy are of less importance than the nave, though the fact that some of their bays were vaulted, or revaulted, at nearly every period of mediaeval architecture makes them interesting for a study of consecutive methods. In the bays to the east the vaults are groined on stilted, round headed transverse arches in the early Romanesque manner, while the succeeding bays have pointed transverse arches with groined vaults closely resembling those of the school of Bourgogne, and the bays nearest the west end have ribbed vaults, in one case with the early heavy-torus rib, in another with the light rib of pointed section of a late Gothic rebuilding.

Although not the basis of a school of Romanesque architecture, the cathedral of Le Puy was not without its influence. This is especially apparent in the large church of Saint Hilaire at Poitiers (Figs. 7, and 8), which was constructed with very broad nave and aisles,--both covered with wooden roofs,--after a disastrous fire of 1018, and dedicated in 1059. In 1130 the vaulting of this church was undertaken, the result being a most unusual edifice. As the nave was too broad to be easily covered by a vault of single span, it was subdivided by lofty and slender piers and arches into a central portion consisting of square bays,[28] and narrow rectangular bays forming veritable inner aisles on either side. These narrow bays were covered with groined vaults directly above the original clerestory windows which thus continued to light the newly formed nave. Domes were then placed over the square central bays as had been done at Le Puy, but instead of the niche-head-squinch and the practically equilateral octagonal dome, small conical trumpet arches were employed at Saint Hilaire, and the gores of the dome rising from these were much narrower than the four remaining panels. This gives the dome rather the character of a cloistered vault with its corners cut off than of a dome properly speaking. Since the clerestory is below the level of the transverse arches upon which the domes of Saint Hilaire are built, the interior has a loftier and less broken appearance than that of Notre Dame-du-Puy. But even so the effect is not remarkably pleasing.

The side aisles of Saint Hilaire (Fig. 8) are quite as interesting in their vaulting as the nave. A single broad aisle on either side, which apparently opened into the nave through lofty arches rising almost to the clerestory, and which probably had transverse arches with ramping walls carrying half gable roofs, was altered when it was determined to vault the church. In doing this, two arches with a solid wall above were placed under each of the original arches of the nave arcade, a slender column built up in the center of each of the original bays, and upon the pseudo-double side aisles thus formed, compound groined vaults were constructed in a manner best understood from the photograph (Fig. 8).

Except for those just mentioned there are but few Romanesque churches,--outside of Italy and Sicily,--in which the nave is covered by a series of domes.[29] But because of the powerful Byzantine influence, these latter

countries contain a large number of churches of semi-Byzantine, semi-Romanesque character, some of which are as late as the thirteenth century.[30] Most of these are so distinctly Byzantine that they do not properly fall within the province of this book, in spite of their late date; but others, like the cathedral of Molfetta,[31] have a vaulting system quite closely allied to the Romanesque.[32] In this particular cathedral, a nave of three square bays is covered by three domes, one on flattened spherical pendentives, the others on niche-head-squinches. Two of them rise from drums and unlike their Byzantine prototypes, they are all of stone.[33] Moreover, the side aisles are covered with half tunnel vaults on full transverse arches, the crown of the vaults together with the nave walls above them acting as admirable buttresses for the domes. A system not quite so logical exists in the aisles of the church of San Sabino at Canosa (1100), where there are full tunnel vaults which do not serve so adequately as buttresses.

PYRAMIDAL VAULTS

Although not vaulted with domes, the church of Saint Ours at Loches in France (Indre-et-Loire) (Figs. 9 and 10) has a close connection with such churches as those of Perigord and Notre Dame-du-Puy. This collegiate church was probably constructed a little before 1168, and originally consisted of a nave divided into square bays by transverse arches of pointed

elevation and side aisles which have now disappeared. Each nave bay is converted from a square into an octagon by flat triangular pendentives on very small trumpet arches. But instead of domes, the builders of Saint Ours substituted a hollow octagonal pyramid of stone over each bay. Such a system, while presenting the same aesthetic objection as that of Le Puy, had greater structural advantages. The pyramids could be built entirely without centering, and exerted almost no outward thrust, while the stones of which they were constructed could be faced on the exterior (Fig. 9) as well as the interior, and the steep roof thus formed provided adequate drainage for the rain and snow of the region.[34]

TUNNEL VAULTS

If the dome played but a small part in Romanesque architecture, such was not the case with the tunnel vault. Almost as old as civilization itself, this method of vaulting had been employed to a greater or less extent in every age from the Egyptian period to that of the Carolingian Empire. It is natural, therefore, to find it the principal method in use during the entire Romanesque era. Nor is it necessary to trace its history back to Persian or Armenian sources. The builders of the eleventh and subsequent centuries had plenty of examples nearer at hand. Roman vaults, some of them of stone, were still in a good state of preservation in many parts of the western world, and almost every country or province possessed examples dating from Carolingian days.[35] It is not the use of this roofing system, therefore, but the skill with which it was adapted to the naves and aisles of churches of basilical plan, that furnishes the most interesting features in the study of Romanesque tunnel vaulting. In fact, so distinct are the combinations and methods employed in different regions, that they constitute veritable architectural schools which may be classified and separately discussed.[36]

ROMANESQUE SCHOOLS OF TUNNEL VAULTED CHURCHES

The four major schools lie in France and center around the ancient provinces of Provence, Poitou, Auvergne, and Bourgogne, whence they derive their names. All four are comprised in practically the same period,--namely, the eleventh and part, at least, of the twelfth centuries,--and it would be impossible to arrange them in any chronological order. But from its resemblance to the Roman monuments in the midst of which it grew and the fact that it had comparatively little structural influence upon the other schools, Provence will be the first to be considered.

THE SCHOOL OF PROVENCE

The cities of Arles and Nîmes had been important Roman provincial centers. Moreover, they still retained, and to this day possess, a large number of Roman monuments whose influence upon the Romanesque churches of the eleventh and twelfth centuries is plainly apparent. Thus vaults which carry directly the tiles of the roof, single aisled churches resembling the little Nymphaeum, or so-called temple of Diana at Nîmes, the employment of flat pilasters in place of the more usual applied shafts of curved section, and a host of minor details all reflecting classic usage are marked characteristics of this school.

PROVENCE CHURCHES OF THE FIRST TYPE

When considered from the point of view of vaulting, the churches of Provence fall into five distinct groups. The first, illustrated by the chapel of Saint Gabriel near Tarascon (Bouches-du-Rhône),[37] is composed of churches with no side aisles. These are covered with tunnel vaults of semicircular or pointed section, with or without transverse arches and carrying directly the tiles of the roof. The supporting walls are frequently strengthened by a series of interior applied arches in one or more orders thickening the wall at the impost of the vault. Outside of this interior buttressing, which has already been seen in Perigord, the churches of this type are of little structural interest.

PROVENCE CHURCHES OF THE SECOND TYPE

In the remaining groups, side aisles are always present and these have four distinct vaulting systems. In the first, tunnel vaults are employed throughout the edifice. Saint Nazaire[38] (after 1090), the former cathedral of Carcassonne (Aude), though somewhat removed from the center of the school, illustrates this system. Both nave and aisle vaults rise from the same impost level. The vault of the nave is slightly pointed, those of the aisles are semicircular, and both have transverse arches. It is a simple and practical method of construction, since the aisle vaults furnish admirable abutment for that of the nave, and all three are covered by a gable roof of masonry resting directly upon the vault crowns. Its one great fault is the absence of direct light in the nave, a condition which introduces the problem of lighting a tunnel-vaulted church.

THE LIGHTING OF TUNNEL-VAULTED CHURCHES

This problem was second only to that of constructing the vaults themselves and, furthermore, it had much to do with the forms which these assumed and even with the plan of the church. When there were no side aisles, windows were cut directly through the outer walls, but to introduce a clerestory above an aisle arcade involved a number of structural difficulties. The side aisle vaults no longer aided in supporting that of the nave, and in fact exerted an inward pressure at a point below its impost where such pressure was most difficult to offset. At the same time, the outward thrust of the central tunnel vault was increased in proportion to its elevation from the ground. The simplest method of meeting these difficulties was to increase the thickness of the clerestory walls, or add simple salient buttresses and trust to good construction to offset the increased thrusts. This was the method adopted by most of the Romanesque builders.[39] It was only in the school of Bourgogne, and under its influence, that the problem received a better solution--which will later be discussed at length--and not until the Transitional and Gothic periods that it was completely solved by dispensing entirely with the tunnel vaults.

While its chief effect was upon vaulting, the lighting problems frequently affected the plan of the church as well. When the nave was without direct light, the aisles were almost always narrowed to permit light to enter from windows in their outer wall. Double aisles were practically impossible,[40] unless the inner aisles had triforium galleries supplied with windows.[41]

Nor did the problem of lighting enter merely into the construction of simple tunnel vaulted churches. It was involved with that of all kinds of vaulting throughout the entire Romanesque and Gothic periods. Transverse tunnel vaults like those of Tournus, groined vaults like those of Vézelay, the development of the Gothic chevet from the half domed apse, and the systems of ribbed vaulting which are frequently found in the crossings, aisles, and ambulatories of Gothic churches, all are closely related to the lighting problem.

PROVENCE CHURCHES OF THE SECOND TYPE CONTINUED

Returning to Provence, it will be recalled that Saint Nazaire at Carcassonne was described as a typical example of the second class of churches of this school, entirely tunnel vaulted, with narrow side aisles whose lateral windows afford the only light with which the nave is supplied. There are, however, a few churches, vaulted like Saint Nazaire, in which the builders introduced a clerestory. Among these is the abbey church of Saint Guilhem-du-Désert (Hérault) (rebuilt at the end of the eleventh century).[42] Here the clerestory is of considerable height, the heads of the windows lying beneath the imposts of the tunnel vaults, a fact which renders this church one of the most developed of the school. Yet this development lies merely in the presence of the windows, and not in any structural advances which made their presence possible. It was because of the excellent masonry of the heavy walls and piers, that the Provence builders dared to attempt this innovation. The vaults themselves are no lighter than before and still carry the entire weight of the roof. In fact, the whole system is one of inert stability, analogous to Roman construction, and exhibits little if any advance toward the elasticity and balanced thrusts which were to characterize Gothic architecture.

PROVENCE CHURCHES OF THE THIRD TYPE

The churches in the third Provence group differ from those in the second only in having half tunnel vaults in the side aisles, but this difference is sufficient to change to some extent the character and methods of construction. In the simple churches of this type where there is no clerestory as, for example, in the western portion of the little church of Saint Honorat, belonging to the monastery of the Isle-de-Lérins (Alpes-Maritimes),[43] the half tunnel vault of the aisles furnishes better abutment for that of the nave than the full tunnel vaults of the second type, and at the same time permits loftier arches to be constructed in the nave arcades, giving a better distribution of light without raising the imposts of any of the vaults.

When, however, a clerestory is added, as in Saint Trophime at Arles (first half of the twelfth century), the inward pressure of the aisle vaults is even more severe than in Saint Guilhem-du-Désert and at the same awkward place, so that the only structural advantage at Arles lies in the added height of the nave arches. It is a noticeable feature of Saint Trophime that the aisles have full, instead of half arches[44] used transversely beneath the vaults, very probably because the former exerted less inward thrust, and could also be weighed down by a solid wall which increased the rigidity of the structure by tying the pier of the nave arcade to the outer wall, and strengthened the clerestory for the support of the high vault. The system has already been noted in the cathedral of Molfetta,[45] and will be found repeated either in the triforia or aisles of a number of Romanesque churches of different schools.[46]

PROVENCE CHURCHES OF THE FOURTH TYPE

The employment of a three-quarters tunnel vault over the aisles renders the fourth group of Provence churches a cross between the second and third. Like them it contains examples with and without a clerestory. Of these the cathedral at Vaison (Vaucluse)[47] (twelfth century) illustrates the former, and the abbey church of Silvacane (Bouches-du-Rhône) (second half of the twelfth century)[48] the latter form. The advantage of the three-quarter type lies in the fact that it exerts less thrust against the inner wall than does the half tunnel and still makes possible loftier arches in the nave arcade compared to the height of the aisle vault than does the full tunnel vault. But these slight advantages are offset by its ugly appearance, and it was never in any sense popular.

PROVENCE CHURCHES OF THE FIFTH TYPE

The system of the fifth type of the school of Provence is that of a tunnel vaulted nave with side aisles covered by transverse tunnel vaults. This method is, however, so different from the other four and was so widely extended,--largely through Cistercian influence--that it can hardly be said to be inherent in any one school, but rather to constitute an individual group of churches which will be separately considered.

From the foregoing discussion of the entire school, it will be seen that the builders of Provence produced very little that was original in vault construction. It was not a school of progress, but rather one of conservative adherence to the Roman tradition of the province around which it centered. Its most progressive feature was, perhaps, the preference it displayed for the pointed tunnel vault,[49] and this may be explained by the fact that the vault in Provence generally carries directly the tiles of the roof and less masonry was necessary to carry a pointed vault up into a gable than would have been the case with one of semicircular section. One further preference, which shows the structural sense of the Provence builders, is that for transverse arches under the vaults, which not only make possible lighter masonry in the vaults themselves, but also lessen the centering necessary for their construction.

VAULTS SIMILAR TO THOSE OF PROVENCE IN OTHER ROMANESQUE CHURCHES

Such methods of vaulting as those just described are not confined to Provence. In Poitou, for example, there is a group of churches with half-tunnel vaults in their side aisles. Some of these, like Saint Eutrope at Saintes (Charente-Inférieure)[50] (eleventh century) and Aigues-Vives (Loir-et-Cher),[51] have corresponding half arches, others, like Parthenay-le-Vieux (Deux-Sèvres),[52] (cir. 1129) have full transverse arches beneath these vaults. Moreover, in Auvergne the triforium is regularly covered with a half tunnel vault buttressing the tunnel vault of the nave, and in a few instances, as at Culhat (Puy-de-Dôme),[53] the side aisles are in one story with similar vaulting. There are also many instances outside of Provence in which the aisles have full tunnel vaults. Between Auvergne and Bourgogne there is an example in the abbey church at Souvigny (Allier) (eleventh century) (Fig. 11), and such a system may quite possibly have been employed in the aisles of Cluny[54] and in those of the choir of Saint Benoît-sur-Loire (Loiret)[55] (second half of the eleventh century). Even in England it occurs in the Tower Chapel at London[56] (begun 1078), and is also found in Poitou at Melle (Deux-Sèvres), Saint Pierre[57] (early twelfth century), where the vaults are pointed, and at Lesterps (Charente),[58] where they are of semicircular section. The three-quarter tunnel vault also is not confined to Provence for it appears as far north as Saint Genou (Indre) in the eleventh century.

The foregoing examples serve only to indicate that such systems as these which are inherently simple in construction came, very naturally, to be widely employed during the Romanesque era. Where they originated it is impossible to say, but the fact that they are so elementary in principle and often vary in some of their structural characteristics[59] may indicate that they were developed independently and contemporaneously in various localities.

NAVES WITH TUNNEL VAULTS AND AISLES GROINED

The next three schools of Romanesque architecture have one feature in common, namely, the employment of groined vaults over the side aisles. But the form which these assume and their relations to the tunnel vaults of the nave differ sufficiently to distinguish the churches of Poitou, Auvergne and Bourgogne from one another.

THE SCHOOL OF POITOU

The chronology of the churches of Poitou is somewhat obscure, but the vaulting principles of the school were well developed early in the eleventh century, to which period a number of the existing churches belong. Their naves are tunnel vaulted and without a clerestory, the light entering through windows in the outer walls of the aisles, which are narrow and high and covered with groined vaults rising from the imposts of the arches opening into the nave. The entire church has a single-gabled exterior roof of wood and tile, its rafters supported near their centers by a wall above the nave arcade, and thus not resting directly upon the extrades of the vaults.[60] Certain minor structural differences make it possible to divide the churches of Poitou into two groups.

The first is composed of the earlier churches, of which Saint Savin-sur-Gartempe (Vienne) (begun cir. 1023) is the best and perhaps the only existing example. In it, both nave and aisle vaults are without transverse arches. All the vaults are semicircular in section, and those of the aisles[61] have their transverse surfaces continuous with the soffits of the nave arches.[62] This gives them the flattened groins so characteristic of Roman architecture. Such a system as this required an extensive wooden centering, and it is not surprising that the builders of Poitou soon introduced transverse arches beneath the vaults,--perhaps through the influence of Lombardy, where they were in use as early as the tenth century[63]--thus producing a group of churches which form the second type of the school.

Notre Dame-la-Grande at Poitiers (Vienne) (early twelfth century), is an early example of this class. Transverse arches are employed throughout the church, not only strengthening the vaults but making it possible to save centering by using the same form for each successive bay and at the same time reducing to some extent the thickness of the web by thus breaking it up into smaller units.[64]

Toward the second half of the twelfth century the system was still further improved by the introduction of pointed arches and vaults in both nave and aisles, as for example in the abbey church of Cunault (Maine-et-Loire). The flattened type of groin has here been abandoned, though the vaults are not of domed-up type. Such doming is to be found in Poitou, however, in Saint Pierre at Chauvigny (Vienne),[65] probably with the intention of saving centering, as in Byzantine architecture. But even though the builders of Poitou made some progress in vaulting, they never attempted to solve the associated problem of getting direct light in the nave. Hence such progress was but slight from the earliest to the latest churches of the school.[66]

THE SCHOOL OF AUVERGNE

THE ORIGIN AND USE OF THE TRIFORIUM GALLERY IN AUVERGNE

One of the distinguishing features of the typical churches of Auvergne is the presence of a second story or triforium gallery above the side aisles. To account for its presence a number of theories have been advanced. That such galleries were not intended for congregational purposes, at least in the early churches of the school, is evident from the fact that they are but dimly lighted and accessible only by narrow staircases in dark corners. They may have been used for storerooms or treasuries for relics brought by pilgrims,--a possibility which is strengthened by the fact that they ceased to be built in the thirteenth century when the era of the Crusades was past,[67]--or they may have been useful places from which to defend the church, corresponding in this respect to the room frequently found in the second story of Romanesque towers.[68] But whatever their use, they would seem, in Auvergne, at least, to have originated on purely structural grounds.

The expedient of dividing the openings from the nave of the church to the aisles into two stages, with the evident intention of thus reducing the height of the piers and even of making lighter piers possible, was employed in a number of churches both earlier and later than those in Auvergne. It may even be in part the explanation of the double colonnade in the Lateran Baptistery, and the upper stories in the chapel at Aachen, and the abbey churches at Essen, Nymwegen, and elsewhere. In any case, it explains the system of two stories of arches in the Carolingian church of Saint Michael at Fulda (818-822),[69] and in the early Romanesque churches of Vignory (Haute-Marne)[70] (eleventh century), Montiérender, (Haute-Marne)[71] (early eleventh century), and Chatel-Montagne (Allier)[72] (early twelfth century), and probably also in Saint Pierre at Jumièges (Seine-Inférieure)[73] (cir. 940).[74]

A significant fact in connecting these churches which are wooden roofed, with the vaulted churches of Auvergne, lies in their geographical distribution. While the earliest examples such as Fulda lie in the Carolingian region, the latter examples, Jumièges, Vignory and Montiérender lie but slightly north of Auvergne, while Chatel-Montagne is actually in this province.[75] What is more natural to suppose, then, than that the vaulted churches of Auvergne were based upon these earlier churches, and that the nave arcade in two stages was retained even when both aisles and nave were covered with vaults? Furthermore, it would then be perfectly natural that the builders should have built these vaults in two stories corresponding to the two stages of arches, since they would have promptly recognized the great advantage gained by this system, which stiffened the interior and exterior walls for the added weight which the high vaults brought to bear upon them, without injuring to any extent the appearance of the church.[76] This seems all the more plausible when the fact is considered that the churches of Auvergne generally have broader aisles than those of Poitou or Provence. This may also have been a heritage from the early churches with two-storied arcades and wooden roofs just mentioned,[77] and in any case it further explains the system of aisle vaults in two stories. For, while the vaults of narrow aisles might be raised a considerable distance from the ground without danger from excessive thrusts, in wide aisles they would have exerted such thrusts and pressures on piers and walls as to have rendered their support most difficult, particularly when they carried directly the tiles of the roof as in Auvergne.

THE SCHOOL OF AUVERGNE CONTINUED

As to the actual vaulting system of the Auvergnate churches, it is as follows. In the nave, heavy tunnel vaults resembling those of Provence in that they usually carried the roof.[78] Otherwise the churches are more like those of Poitou in the form of the piers, the almost universal absence of a clerestory, and the employment of vaults of semicircular section with transverse arches, as in the early churches of the second class in that school. In the triforium, the builders realized the advantage gained by the use of a half tunnel vault as an offset to the nave thrusts and as a means of best filling the space beneath a single gable roof,[79] and this is therefore the universal method. At times this vault is borne on full semicircular transverse arches,[80] and at others on those which follow its curve.[81] In the side aisles, groined vaults were employed because they were the only kind which could be built without cutting into either the triforium or the side wall windows. In form they closely resemble those of Poitou and were provided with transverse arches.

CHURCHES OF THE AUVERGNE SCHOOL

The church of Notre Dame-du-Port at Clermont-Ferrand (Puy-de-Dôme)[82] (Fig. 12) (cir. 1100) has the Auvergnate characteristics just described. Its great fault lies in the darkness of the interior, a darkness more pronounced than that of the churches of Provence or Poitou because of the width and lowness of the aisles with the consequent distance of the lateral windows from the nave and the fact that they cannot be cut very high above the floor. The windows of the triforium are also small,[83] and their light is almost entirely confined to the gallery by its floor and by the smallness of the arches opening into the nave. This fault was remedied in the choir, where the light was most needed, by doing away with the triforium, and placing a clerestory beneath the half dome of the apse.[84] As a further improvement a lantern was placed over the crossing.[85]

In certain churches of the school like Saint Sernin at Toulouse (nave twelfth century), the triforium was increased in size, perhaps in order that it might be used for congregational purposes, but more probably because larger windows were absolutely necessary in this portion of the church for the sake of the lighting. This theory is strengthened by the fact that Saint Sernin has double side aisles and the lateral windows are therefore too far away to light the nave. These added aisles are covered with vaults of regular Auvergnate character, even to the extent of half tunnel vaults beneath their roofs, and the remainder of the church corresponds to the structural standards of the school.[86]

CHURCHES OF AUVERGNE WITH A CLERESTORY

Although it might seem from the foregoing pages that the builders of Auvergne were very backward in structural technique, there are a number of churches in the school which have a clerestory in the nave. Among them is Saint Étienne at Nevers (Nièvre)[87] (end of the eleventh century),[88] in which the clerestory is obtained by raising the wall above the triforium arches just high enough to permit the introduction of comparatively small windows with their heads rising above the impost of the vaults.[89] The principle is the same as that in Provence, and no structural innovation is involved. The builders merely relied upon heavy piers and walls and salient buttresses to bear the added thrust which the tunnel vaults, thus raised, produced. That their reliance was not especially well founded is proved by the numerous cracks in the masonry.

THE SCHOOL OF THE LOIRE

The introduction of a clerestory in tunnel-vaulted churches was not yet scientifically accomplished, and it remained for the school of Bourgogne to find the best possible solution of the problem. But this solution would seem to have been reached only after some intermediate steps had been taken which may, perhaps, be traced in a number of eleventh century churches. Two of these lie slightly to the north of Poitou and Auvergne and strongly reflect the influence of these neighboring schools. These churches, together with others in the same general region, may perhaps be said to constitute a school of Romanesque architecture, which might properly be termed the School of the Loire.

The first of these is the small church of Saint Genou (Indre).[90] It is a combination of the types of Auvergne and Poitou except that the tunnel vault of its choir is raised on a clerestory wall pierced with good sized windows. Its aisles are in only one story, and, instead of being groined, are covered by three-quarter tunnel vaults perhaps showing the influence of such Provence churches as those of Silvacane and Vaison. The whole system shows an advance in structural skill in several particulars. In the first place the aisles are built low, and with columnar piers close together, thus insuring the support of a heavy triforium wall. This wall is lightened in appearance but not structurally weakened, by a wall arcade opposite the vaults and roofs of the aisles, and is sufficiently thick at the clerestory level to be pierced with window openings and still afford an excellent impost for the tunnel vault. This, in turn, is built of light material like the vaults of Poitou. With exterior salient buttresses, the system is complete. Its only important drawbacks are the closeness of the supporting piers and the necessity of keeping the whole choir rather low to avoid excessive thrusts.

The second church lies between Saint Genou and the school of Bourgogne. It is the abbey church of Saint Benoît-sur-Loire (Loiret), begun in 1062 and possessing a choir, transepts, and porch, dating from the second half of the eleventh century. Its choir (Fig. 13) closely resembles that of Saint Genou in every particular, except that the aisles have full tunnel vaults and the church as a whole is larger with a much more lofty nave of greater span.[91] Such a system as that of Saint Genou and Saint Benoît is produced by the extension of the elevation so frequently seen in the apses of the churches of Poitou and Auvergne to embrace the sides of the choir as well. The columnar piers and small arches used are like those in the apse rather than like those in the remainder of the church. The builders seem, however, to have failed to realize that walls which would support the half dome of the apse would not necessarily prove sufficiently strong to resist the thrusts of a tunnel vault. In fact, in spite of its apparent advance, the vault of the choir of Saint Benoît was only prevented from falling by the addition of transverse arches and flying-buttresses at a date subsequent to the completion of the church, and the vault of the nave of Cluny, which was quite possibly similar, actually fell in 1125.[92] It remained for the twelfth century builders of Bourgogne to take the final steps which were to carry the system of tunnel vaulted naves with direct light to its highest development.

THE SCHOOL OF BOURGOGNE

It is most unfortunate for a study of the school of Bourgogne that the mother church at Cluny (Saône-et-Loire) should have been almost totally destroyed in the French Revolution. This great church was begun in 1089 and must have been finished in 1125, for the nave vaults fell in that year and were rebuilt before the final consecration in IIVO. What its original vaulting system was is difficult to say. Reber[93] says that it was probably vaulted like the churches of Auvergne with inner aisles in two stories, but Rivoira[94] states that both the nave and aisles had tunnel vaults on transverse pointed arches. The exterior view,[95] and the model which fortunately remains, would correspond with either arrangement.[96] The important facts to note are that the nave had a clerestory, and that the nave vault was strengthened on the exterior by carrying up the clerestory walls to exert a downward pressure at its haunch, a most important structural advance over the exterior wall of Saint Benoît-sur-Loire.[97]

The developed system of Bourgogne may be seen to advantage in the abbey church of Paray-le-Monial (Saône-et-Loire) (Figs. 14, 15), which dates from the early twelfth century and is thus only slightly later than Cluny itself. Its nave is wider and loftier than any yet seen in which a tunnel vault was used, though not equal in size to that at Cluny, which was thirty-two feet wide and ninety-eight feet high. All the structural arches are pointed, but those used for windows, doors and decoration are still round headed.[98] The clerestory, while it has only moderately large windows, is so high above the ground as to render the support of the vaults above it exceptionally difficult. This difficulty was overcome, first by giving the vault a pointed section and thus reducing the thrust; second, by building as light a web as possible and covering it with a wooden roof; third, by using tie-rods of wood or metal, running along near the impost of the vault in the thickness of the walls, thus to a certain extent concentrating the pressure upon the piers; and, finally, as has already been stated, by carrying the exterior walls of the church to a point considerably above the window heads (Fig. 15), thus obtaining a downward pressure which offsets the outward thrusts.

The side aisles of the school of Bourgogne are also worthy of mention. They are usually covered with groined vaults, in many cases of slightly domical form. Whether this method came directly from Lombardy where there exist early examples of its use, or whether it came in through the influence of Poitou and Auvergne which had come into close contact with Carolingian architecture, is an open question. It seems quite likely, however, that, since the Byzantine builders developed this type and transmitted it to the Carolingian builders of the Rhine valley, it should have passed from there into France and spread over the three northern-central schools as it did over Lombardy. Regardless of its origin, it became the standard type in all the important churches of the Cluniac region. Occasionally, as at Souvigny (Allier) (possibly eleventh century), the enclosing arches are of stilted round headed form, a type which is also found as far north as Vézelay (Yonne) La Madeleine (after 1140) (Fig. 16). Neither of these churches, however, is near the center of the school,[99] and the pointed structural arch as used in the abbey church of Paray-le-Monial (Fig. 14) is the common form.

The system employed in Bourgogne marks the highest development attained in the use of a tunnel vault running the length of the nave. In the Ile-de-France a few instances might be cited[100] in which a system like one of those already described was used, and the same is true of certain Romanesque churches outside of France, but in none of them is any new structural method introduced. The tunnel vault was even used occasionally as late as the thirteenth century,[101] but the examples are generally small and insignificant.

CHURCHES WITH TRANSVERSE TUNNEL VAULTS OVER THE NAVE

Besides the methods which have just been described and which were so localized as to form veritable Romanesque schools, there remain a number of churches falling into two groups in which transverse tunnel vaults replace those running longitudinally either in the nave or aisles. The first and smaller group contains those in which such vaults were used over the nave. Of these, the most important example is Saint Philibert at Tournus

(Saône-et-Loire),[102] a church of considerable size and of early date (dedicated 1019). Cylindrical piers and transverse arches divide the nave into rectangular bays each of which is covered by a transverse tunnel vault with a window in the clerestory wall at either end. Excellent light is thus obtained and the thrusts of the vaults admirably counteract one another. In fact, the system is so logical that it is surprising that it gave rise to so few imitators.[103] The explanation may perhaps lie in the lack of apparent continuity in the vault, a fault which this method shares with that of Le Puy. As to its origin, it may go back to such Persian monuments as Tag-Eivan, or to Syrian copies of Sassanian work with the substitution of stone for brick as Choisy suggests,[104] though it is not unreasonable to think that the builders of Tournus originated the system since it involved no unknown structural principles. The aisles of Saint Philibert furnish one of the rather rare examples of the employment of interpenetrating vaults.[105]

CHURCHES WITH TRANSVERSE TUNNEL VAULTS OVER THE AISLES