Clarence Ward

It is not the province of this essay to enter into a discussion of the origin of the ambulatory and its introduction into the church plan.[402] It is sufficient to note that a passage around a semicircular apse appears even in Roman times in the imperial tribune of the so-called stadium of Domitian on the Palatine at Rome which dates from the second century A.D.,[403] and that a similar passage was added around the apse of San Giovanni in Laterano by Pope Sergius II (844-845).[404]

Such ambulatories were mere service galleries, not directly connected with the apse and in fact shut off from it by a solid wall, but when once adopted as a feature of the church plan, the ambulatory rapidly became an aisle around the apse corresponding in all respects to that which flanked the rectangular nave or choir.[405] It was natural, therefore, that this added aisle should have been vaulted and such is the case in the two earliest ambulatories of any size which still exist, namely, those in Santo Stefano at Verona (end of tenth century) and the cathedral of Ivrea (973-1001 or 1002),[406] while the early ambulatories in France, like those of Saint Martin at Tours (end of eleventh century) and the cathedral of Clermont-Ferrand, which have unfortunately been destroyed, were doubtless also vaulted.

Origin of Ambulatory Vaulting

That the form which such vaulting assumes owes its origin to that of the concentric aisles in earlier buildings of circular plan would seem a most natural supposition since the problems in the two cases were precisely alike. As a matter of fact, a comparison shows that all or nearly all the methods of vaulting developed in the Roman or Byzantine period for the aisles of circular buildings were tried by the Romanesque builders when they added an ambulatory to the semicircular apses of their churches.

Annular Tunnel Vaults

The principal Roman type would seem to have been the annular tunnel vault. An excellent example is to be seen in the amphitheatre at NÎmes in which the builders have even employed transverse arches of stone beneath the vault of brick.[407] Similar in character, though later in date and without transverse arches, is the fourth century annular vault of Santa Costanza in Rome. It is not surprising, therefore, to find the annular tunnel vault in a number of the earliest Romanesque ambulatories as, for example, at Ivrea and in the lower story of Santo Stefano at Verona, both dating from the close of the tenth century, and somewhat later at Vignory in France and in the gallery of the Tower chapel in London.[408] The annular tunnel vault never became in any sense a popular form, however, probably because it necessitated an impost above the level of the apsidal arches and exerted a continuous thrust throughout its whole extent. It is more often to be found in crypts, as in Saint Wipertus near Quedlinburg (936)[409] and in Chartres cathedral (1020-1028)[410] where there were no structural problems of support, or else with its imposts lowered and cut by lunettes into an interpenetrating form which is really an elementary groined vault and is later discussed.

Ambulatories with Half Tunnel Vaults

Besides these annular vaults, there are a few examples of ambulatories with half tunnel vaults which may owe their origin to the desire of the builders to keep the outer impost of the vaults as low as possible and still raise the inner line above the apsidal arcade.[411] In any event such an ambulatory is occasionally found in churches where the aisles also are half-tunneled, as, for example, in the abbey church of Montmajour (cir. 1015-1018)[412] and in the twelfth century church of Saintes.[413] Though this type of vault apparently has no pre-Romanesque prototype, it is perhaps possible that the concentric aisle of the circular church of Rieux-Merinville (Aude) (eleventh century)[414] affords an earlier example of its use over a space of similar plan. There is also an interesting use of a half-tunnel vaulted triforium above the ambulatory and abutting the half dome of the apse which opens into it through five arches, in the church of Loctudy (FinistÈre) twelfth century.[415]

There are, however, circular buildings of the Byzantine and Carolingian periods with vaulted aisles which may well have furnished the prototypes for other methods of ambulatory vaulting which the Romanesque builders employed. One of these is the Royal Chapel at Aachen (796-804), in which the aisles are two stories high with the lower story covered by groined vaults of alternately square and rectangular plan with no transverse arches separating the bays.[416]

Romanesque Ambulatories with Alternating Triangular and Square Bays

Although there appear to be no Romanesque churches with ambulatories of exactly this type, there are a number which are composed of triangular sections of an annular vault alternating with groined bays of practically square plan. One of these is the upper ambulatory of Santo Stefano (end of tenth century) at Verona, while a similar arrangement may be seen in the concentric aisle of the crypt of Saint BÉnigne at Dijon (CÔte d’Or) (1002-1018).[417] Moreover, the type at Aachen of alternate square and triangular groined bays, is to be seen at Paris with the addition of transverse arches between the bays, in Saint Martin des Champs (cir. 1136) and at Gloucester in the beautiful ambulatory of the cathedral (1089-1100). Furthermore, this alternation of square and triangular bays was of quite frequent occurrence in the ribbed vaulted ambulatories later described.

Ambulatories with Transverse Tunnel Vaults

The gallery of the Palatine chapel at Aachen is covered in still another manner by a series of ramping tunnel vaults alternately triangular and square in plan and springing from a series of transverse arches. Although never exactly copied in ambulatory vaulting, a similar system in which ramping groined vaults displace the simple tunnel form appears in the gallery of the north transept of San Fedele at Como (twelfth century)[418] while the system of ramping the vault had still another application in the trapezoidal groined vaults of San Tommaso at Almeno-San-Salvatore,[419] the evident object being to get a slant above the vaults suitable for an exterior roof which might rest directly upon them. But if ramping tunnel vaults were not used over the ambulatory, there are at least two instances of the employment of expanding transverse tunnel vaults in this position and these may well be products of the Aachen type. The ambulatory at Vertheuil[420] affords an example dating from about the middle of the twelfth century, which must soon have been followed by the gallery of the cathedral of Notre Dame at Mantes (beg. in 1160?).[421] Here the vaults are similar, but on a much larger scale, and with quite different transverse supports consisting of lintels, each resting upon two columns placed between the apsidal piers and the outer walls. [422]

Ambulatories with Groined Vaulted Trapezoidal Bays

All of the ambulatory types thus far described were but occasionally used in the Romanesque period. Far more common, and in fact the standard form, is that of simple four-part groined vaults over bays of trapezoidal plan. Here again the plan at least has a Byzantine prototype in the church of San Vitale at Ravenna where the concentric aisle is divided into trapezoids, though these in turn are cut by the radiating niches of the central nave and the groined vaults employed are therefore of irregular form.

Even without any prototypes, however, this arrangement of bays is a direct outcome of the use of an annular tunnel vault intersected by lunettes or transverse tunnels opposite the apsidal arches. Such vaults may in fact be seen at a comparatively early date in the churches of Bois-Sainte-Marie (SaÔne-et-Loire) (twelfth century), Champagne (ArdÈche), and Preuilly-sur-Claise (Indre-et-Loire), and in a reversed sense at Saint Savin (Vienne) (cir. 1020-1040) where there is an early instance of a simple annular vault cut by expanding transverse tunnel vaults whose intrados at the smaller end corresponds to that of the apsidal arches but whose crowns rise higher than that of the vault which they intersect. There are no transverse arches and yet the vault is really composed of a series of trapezoidal bays. The ambulatory of Saint Sernin at Toulouse (choir consecrated 1096) shows this same system in its fully developed form. There are still no transverse arches, but the vault is no longer interpenetrating but fully groined, yet with practically level crowns, so that it still has the general form of intersecting tunnel vaults.

It was far more common, however, for the Romanesque builders to separate their trapezoidal bays by transverse arches, though their use would seem to have been optional rather than to indicate a more developed architectural type, since they are found at an early date in the ambulatory of Saint Philibert at Tournus (SaÔne-et-Loire) (1009-1019), where the form of the vault would otherwise be of interpenetrating type. It is, in fact, less developed than that at Saint Sernin, the transverse panels being considerably lower than the concentric portion of the vault thus forming simple lunettes above the window heads. In such a vault, the transverse arches are structurally valuable only in so far as they make possible the erection of the vault in sections and consequently serve as permanent centering and as a stiffening member between the apsidal piers and the outer walls. In the fully developed vaults with transverse arches, like those at Paray-le-Monial these arches serve still another purpose. Here it is evident that the vault was laid up in sections, for each bay is domed up at the crown and the transverse arch not only carries a little of the weight of the vault but also conceals what would otherwise be an awkward intersection line between one bay and the next. With this doming up of the vault crown and the use of pointed transverse arches to replace the awkward stilted form, the vault of Paray-le-Monial marks the highest point possible before the introduction of the diagonal rib in the Transitional and Gothic periods.

Ambulatories with Ribbed Vaults

It has already been stated that it is not the purpose of this paper to discuss the origin of ribbed vaulting. In fact, it is rather the intention to accept the conclusions of Mr. Porter in his “Construction of Lombard and Gothic Vaults” that this innovation arose from the necessity for providing a centering where wood was not to be easily obtained or where the shape of the bays or their position in the church made a permanent centering of stone or brick far superior to, and easier of construction than, a similar centering in wood.[423] Accordingly the fact that some of the earliest ribbed vaults appear over the ambulatory is readily explained by the trapezoidal shape of the vaulting bays, for which a wooden centering would have been especially difficult to construct.

Morienval

Of these rib-vaulted ambulatories, the earliest which has come down to us would seem to be that of the little church of Morienval (Figs. 77, 78, 79), which probably dates from about 1120-1130. A study of this ambulatory shows most clearly the gradual changes and adjustments which mark the development of perfected rib vaulting from its groined prototype. In size this is an insignificant work and yet historically most important. Perhaps its first noticeable feature lies in the use of slightly pointed apsidal arches (Fig. 77), showing that the builders grasped in at least a

Fig. 77.—Morienval, Church.

rudimentary way the advantage to be gained in thus bringing these arches up to a point where they would be nearly, at least, on a level with the crown of a semicircular formeret. The use of these formerets or wall arches is a second advance in this vault at Morienval, and though these are unnecessarily heavy and in two orders (Fig. 78) they do reduce the width of the vaulting bays and furthermore they clearly define the wall line of the panels and may even have aided in the support of the wooden centering or cerce on which the severies were laid up. They do not apparently support the actual masonry of the cell, which, as is clearly shown in the southwest bay, does not follow the curve of the formeret.[424] The transverse arches (Fig. 78) show little structural advance, for they are still round headed. They are however highly stilted yet in addition to this the builders have found it necessary to pile their crowns with masonry in the manner already described in connection with the vaults at Bury.[425] It is in the use and

arrangement of the diagonals (Fig. 79) that the chief interest in this early ambulatory lies. If not unknown in bays of rectangular plan, this was probably a first attempt to apply these intersecting ribs to bays of trapezoidal shape, a problem especially difficult when these bays had two curved sides. The ambulatory was so narrow and the wall piers with the two wall arches extended so far into its width that the space actually to be covered was of such a plan that ribs directly from the one pier to that diagonally opposite would have intersected almost against the crown of the apsidal arch. To avoid this awkward arrangement, and make the panels of more equal size, the builders either timidly broke the line of the rib, as in the second bay from the southwest (Fig. 79), or curved the ribs slightly away from the crown of the apse arches as in the northwest bay. Whether the builders were actually experimenting here at Morienval with the position of the diagonals and whether this little work of the early twelfth century had any influence upon later ambulatory vaulting may be an open question, yet it is a fact that the later ambulatories with ribbed vaults over trapezoidal bays show three distinct types in the arrangement of the diagonals according as these are left straight in plan, or curved, or broken to bring their crowns to a better point in relation to the crown line of the enclosing arches.

Trapezoidal Ambulatory Vaults with Straight Diagonal Ribs

Of the three types, the one with straight diagonals (Plate III-a.) is perhaps most seldom seen, probably because of the awkward place at which its vault crown falls. It does appear, however, in the cathedral of Aversa near Naples[426], where the heaviness of the ribs would seem to denote an early date.[427] There are a few later examples elsewhere, among

them the cathedrals of Langres (Haute-Marne) (end of twelfth century) (Fig. 80) and Milan (beg. 1386), while a similar system with one or more added ribs in the outer severy is to be seen at Pontoise (Seine-et-Oise) S. Maclou (Plate III-h.), in the cathedral of Rouen (Plate III-d.), and in Saint Remi at Reims (Fig. 83), which are later described.

Trapezoidal Ambulatory Vaults with Curved Diagonal Ribs

A little more common, perhaps, are the ambulatories with diagonal ribs of curved plan (Plate III-b.). The earliest existing example subsequent to Morienval would seem to be that of the abbey church at Saint Germer-de-Fly (cir. 1130-1150).[428] Its ribs correspond in general to the curve of the groins which would be produced by the intersection of a transverse with an annular tunnel vault. Such ribs are naturally difficult to construct because of their curvature in plan as well as in elevation and as a result they are but seldom found, though an example on a large scale appears in Bourges cathedral (Plate IV-a.).

Trapezoidal Ambulatory Vaults with Broken Ribs

The solution of the problem of covering a trapezoidal bay with ribbed vaults lay in the employment of the broken rib, or in other words, in the selection of a point of intersection from which four half arches were extended to the supporting piers (Plate III-c.). This system, which was very possibly first employed at Saint Denis (1140-1144),[429] became the standard throughout the best Gothic period wherever trapezoidal bays were used, though there was a certain amount of variance in the position of the keystone. At Saint Denis, and in the great majority of the best Gothic churches it lies practically on the line of a curve through the crowns of the apsidal arches and concentric with that of the apse,[430] but in some instances, notably at Sens cathedral[431] and in the ambulatory of Canterbury[432] which was directly influenced by the first-named church, the point of intersection was moved outward to a point where the line from this crown to the transverse arch is practically perpendicular to the latter. The result is an equalizing in length of the four half ribs, but this is accomplished only at a considerable sacrifice in appearance.[433]

Method of Construction in Ambulatory Vaults

The actual construction of ambulatory vaulting followed much the same course as that of vaults in the remainder of the church and especially those in the side aisles. Thus in the cathedral of Langres (Fig. 80), which dates from the close of the twelfth century and is somewhat south of the center of architectural development in the Transitional period, the ambulatory presents a number of rudimentary characteristics. In fact, judging from the awkward manner in which the diagonals rise from their

imposts, the exceptionally large size of the transverse arches, and the lowness of those opening into the apse, it would seem as though this aisle had been planned for domed up groined vaulting of the Bourgogne type, already seen at Paray-le-Monial, and that ribbed vaulting came in before the completion of the ambulatory and was therefore substituted. In any event, these straight diagonals and low apsidal arches combined with the heavy transverse arches and the decidedly domed up character of the vaults themselves produce a much more primitive appearance than is to be seen further north in the contemporary vaults of Saint Leu-d’Esserent (Fig. 81). In the latter, the builders have stilted the apsidal and transverse arches, thus greatly reducing the doming of the vaults. They have also provided an impost for the diagonals which are themselves of the broken type, and in fact the form of the vaults is practically perfected except in the matter of the transverse arches. These are still much heavier than the diagonals, a feature which continues to be manifest though in a less marked degree in many of the ambulatory vaults even of the thirteenth century. They correspond in this respect to side aisle vaulting.[434] Only occasionally, as in the splendid inner ambulatory of Le Mans cathedral (1218-1254), were the ribs all made of the same size. This advance combined with its height and general character may perhaps entitle the ambulatory of Le Mans to rank as the finest in Gothic architecture and the high water mark of the trapezoidal four-part broken ribbed vault.

Trapezoidal Ambulatory Vaults with Added Ribs

If there was one fault in the broken ribbed type of ambulatory vault just described, it lay in the form of its intersection with the outer wall. For example, if the ambulatory was comparatively low or the apsidal arches of wide span, this intersection became either segmental or semicircular or, at best a very low pointed curve, under which it was most difficult to arrange the exterior windows and still produce a pleasing interior effect. Thus in the ambulatory of Sens cathedral,[435] the two round headed windows do not fill the space beneath the wall rib and are in fact awkwardly placed beneath it, while in the ambulatory of Trinity chapel in Canterbury cathedral,[436] where the vaults are but slightly domed, the arrangement is even less pleasing. Of course when these arches opened into radiating chapels, their shape did not make so much difference since their supporting piers ran all the way to the floor and therefore gave a fairly good proportion to the arch. But if the entire space beneath them were occupied by a window extending only part way to the floor, it would be largely head and very little jamb and thus of displeasing proportions. Even in the ambulatory clerestory of Le Mans, where the transverse and diagonal ribs are all of very pointed section, the window is too broad for its height. It would seem, therefore, to have been with an eye to a more pleasing arrangement of the windows beneath these trapezoidal vaults, that many of the mediaeval builders subdivided the outer severy of extra ribs running out from the central keystone. This made possible two or more windows in the outer wall of each bay. Thus in the alternate bays of the ambulatory of Rouen cathedral (Plate III-d.), where there are no radiating chapels, a single rib is added in the outer panel making the vault of five-part form, so that the heads of the two slender windows of the bay are

each situated in a separate cell. This same arrangement is characteristic of a number of other ambulatories, including the lofty inner one at Coutances cathedral (Fig. 82, and Plate III-e),[437] where the windows are limited in height by the elevation and would be of awkward shape were they not arranged in pairs under separate vault cells.[438] Nor did the mediaeval builders restrict themselves to a single added rib in this outer severy of the vault. In the ambulatory gallery of Saint Remi at Reims (Fig. 83) there is an excellent example of the subdivision of this panel into three window cells and in the church of Saint Germain and the cathedral at Auxerre (Fig. 84 and Plate III-f) there are excellent examples of a similar method, applied both in bays with exterior windows and in those which open into a radiating chapel. In the latter instance, the lofty and slender shafts between this chapel and the ambulatory with their many radiating ribs and arches give a charming appearance of grace and lightness to the design.

Ambulatory Vaults which Include the Radiating Chapels

In all the churches thus far discussed, and, in fact, in the majority of those constructed during the Gothic period, the radiating chapels are separated from the rest of the ambulatory by arches directly across their entrances. But quite frequently these chapels, particularly when they were comparatively shallow, as in the cathedral of Chartres (Plate III-g.), or

even when comparatively deep as at Saint Denis[439] and Saint Maclou at Pontoise (Plate III-h.), were treated as part of the ambulatory and an added rib was introduced in vaulting them exactly in the manner described in connection with the trapezoidal bays of Rouen and Coutances. Furthermore, as the chapels were increased in size, more than one extra rib was added in the severy of the trapezoidal vault which embraced them so that there were, sometimes, two such ribs, as in the cathedral of Tournai (1240-1260) (Fig. 85).[440] Occasionally, also, as in the cathedral of Saint Quentin (after 1230) (Plate III-i.), similar bays and vaults occur, with the addition of large radiating chapels opening off of the more shallow curves of the ambulatory bays, suggesting a combination of the Tournai type with that of Auxerre (Plate III-f.). In some of the larger and deeper chapels there were even four added ribs as, for example, in the cathedral

of Bayonne (Fig. 86), where the ambulatory is further noteworthy because the builders, in an attempt to equalize the vaulting severies, have moved the keystones of the diagonals almost out to a point on the line of the outer walls. As a matter of fact, it was moved out to such a point in a number of instances (Plate III-j.), as, for example, in Soissons cathedral[441] where it becomes the keystone of an arch directly across the entrance of the chapel as well as being the center for all the ribs both of this chapel and the ambulatory. Each trapezoidal bay is thus divided not into four but into three triangular panels, the chapel itself being covered by a fully developed five-part chevet vault for which the two ribs of the ambulatory bay act as buttresses. A similar but more logical vault appears in the ambulatory and two eastern chapels of Pamplona cathedral (begun 1397) (Plate III-k.). This is a church with an axial eastern pier, and its radiating chapels are arranged so as to form perfect hexagons with the bays of the ambulatory. The keystone is then moved out, as at Soissons, to the crown of the chapel arch where it lies in the exact center of each hexagonal bay and thus produces a perfectly symmetrical vault.

Ambulatories with Alternate Square and Triangular Bays

Although the trapezoidal bay and its variants has been the only one thus far considered in the discussion of ribbed vaulted ambulatories, it was not by any means universally employed. The alternation of square and triangular bays, which had been used as early as the Carolingian period in the royal chapel at Aachen, and in the tenth century at Verona, in groined vaulted ambulatories, also played a considerable rÔle after the use of ribs became general. This system afforded a number of structural advantages, the chief one being, of course, that the major bays were square or nearly so, and therefore presented no structural problems not already solved in other portions of the church, while the triangular divisions were of comparatively small size and could be covered in the same manner as in the Romanesque period, with three-part groined vaults, provided the builders wished to avoid attempting ribbed vaults over them.

Two general plans are noticeable in the use of this alternate ambulatory system. In the first, which appears at an early date in Saint Martin of Étampes (1165), Saint Remi at Reims (1170-1181), and Notre Dame

at Chalons-sur-Marne (end of twelfth century), the square bays alternate with two triangular bays or, in other words, the ambulatory is first divided into trapezoids by transverse arches and these in turn subdivided into a square and two triangles. This system may be understood from the plan of Saint Remi (Plate III-l.) and the interior view of the same church (Fig. 87). Its most noticeable feature is the lack of ribs in the triangular bays, these remaining of simple Romanesque groined type. Exactly the same arrangement appears at Chalons-sur-Marne, except that here the arches into the apse correspond to the flat sides of a polygon, while those opening into the chapels are on a curve in order that the exterior wall of the triforium above them may be a semicircle.[442] In both these churches, the radiating chapels occupy all the space included beneath each group of three outer arches in a manner similar to that described in connection with the cathedral of Auxerre, but in Saint Martin at Étampes, the chapel is limited in width to the span of the central arch, making possible a window in the exterior wall of each of the triangular bays. A very similar arrangement appears in the outer ambulatory of Bourges cathedral (cir. 1195-1215) (Plate IV-a.), except that here the chapels are so narrow as to give a reversed trapezoidal character to what would otherwise be a square bay like that at Étampes and Saint Remi. Even though the triangular severies are thus increased in size, the builders have left their vaults unribbed.

The second system of alternating square and triangular bays may be seen in the outer ambulatory of the cathedral of Le Mans (Plate IV-b.) and in both ambulatories of the cathedral at Toledo (1227-seventeenth century).[443] It is the familiar early mediaeval system of a single triangular bay between two squares with the addition of ribs beneath the vaults in all the bays. The chief effect of this system upon the construction was to subdivide the outer line of the ambulatory into twice as many parts as there were in the apse. This created a certain difficulty in the adjustment of the buttresses, for the lack of any transverse arch directly across the ambulatory from the apsidal piers to the outer walls made necessary the subdivision of the flying-buttresses into two parts. This subdivision must have added considerably to the expense and difficulty of construction, though this was somewhat offset by the reduced size of the buttress piers and their position in the thickness of the chapel walls, where they in no way interfered with the introduction of windows directly in the outer walls of the triangular ambulatory bays. Though not extensively employed, this vaulting system which is to be seen at Le Mans shared with all others the tendency of the late Gothic period to add extra ribs to those forming the real framework of the vaults. Such added ribs are to be seen in Saint Willibrord at Wesel and Saint Lorenz at NÜrnberg. Similar also to the

Le Mans type, but with the entire omission of the transverse arches between the triangular and trapezoidal bays, is the system at Saint Pierre-sur-Dives (Calvados)[444] which is thus like the outer ambulatory of Coutances cathedral (Plate III-e.), except that the chapels are not included beneath the ambulatory vault and the portions containing the three half ribs are more in proportion to the larger cross ribbed severies.

Ambulatories with Triangular Bays Only

Another method of ambulatory vaulting in the Gothic period consisted in the subdivision of the apsidal aisles into triangles by adding intermediate supports between each pier forming the outside corners of trapezoidal bays. This method, never had a wide popularity. It was used at a comparatively early date and on a large scale in the cathedral of Notre Dame at Paris (begun 1163) (Plate IV-c.), where the triangular bays have no ribs beneath their masonry. It appears with the addition of three half ribs or even a still greater number, in a number of late Gothic churches, especially in Germany,[445] and was also used at Saint Eustache (1532-1637)[446] and Saint Severin[447] in Paris, whose builders may very probably have been influenced by the cathedral church of Notre Dame. In Notre Dame, where there are two ambulatories the doubling of the piers did not do away with the possibility of a central eastern chapel or window in the exterior wall. But in most cases, where there is but one aisle, as, for example, in the Marienkirche at Stargarde (end of fourteenth century) (Plate IV-d.) or the old cathedral of Heidelberg,[448] an axial pier prevents this arrangement. Perhaps to avoid this the builders of Saint Steven at Nymwegen and of the cathedral at Brandenburg left the eastern bay trapezoidal so that there might be a central Lady chapel. At Kolin[449] where there is an axial pier in the apse a central chapel off the ambulatory naturally follows.

Ambulatories with Multiple Ribbed Vaults

As has been noted, the late Gothic passion for multiple ribs affected the ambulatory as it did the remainder of the church, and vaults of most complex character are to be found especially in certain German churches. Of these, GÜben (Plate IV-e.) and the cathedral of Freiburg (second half of the fifteenth century) (Fig. 88) are among the most elaborate.[450] In them, the structural purpose of the rib is totally subordinated to decorative principles and to a desire on the part of the builders to show their knowledge of the intricate problems of stereotomy. With such vaults as these, marking the decline of Gothic architecture, it is not surprising that there was such a complete reaction in vault construction on the part of the succeeding Renaissance builders.

With this discussion of the ambulatory, the study of mediaeval church vaulting is practically complete, but a few paragraphs should be added to give a short account of some unusual eastern terminations and a brief reference to the radiating chapels. Both of these, while presenting no great structural accomplishments, at least show the skill of the builders in meeting any and all requirements imposed by the plan.

Exceptional Eastern Terminations

Of the eastern terminations, a number are especially interesting. One is in the church of Saint Yved at Braisne (Aisne) (1180-1216) (Plate IV-f.), where there is no ambulatory and yet two chapels have been so arranged with their axes at an angle of forty-five degrees to that of the choir aisle as to form a veritable series of four radiating chapels, two on either side of the principal apse. To cover the triangular bays immediately preceding these chapels, a two-part vault corresponding to one of the diagonal halves of a simple four-part vault, is employed, while the chapel itself is covered with a three-part chevet whose crown is abutted by the half rib of the preceding bay.[451] Occasionally, too, a similar arrangement of chapels is found even where there is an ambulatory as in the church of Saint Nicaise at Reims (now destroyed) and at Upsala. Another termination of interest is that in the church of Vigan (Lot)[452] (fifteenth century) where the apse with its chevet vault is west of the transept, into which it opens through its farthest bay while from the transept itself open five small chapels, a unique arrangement.

A third eastern termination of especial interest is that of the church of the Jacobins at Toulouse (Haute-Garonne) (Fig. 89 and Plate IV-g). Here there is a row of central piers the length of the church and the apse embraces the double nave thus formed. This apse the builders have subdivided into a series of triangular bays by arches springing from a pier at the center of its diameter. Each of these is again subdivided like the triangular ambulatory bays of Le Mans cathedral. This completes a vault of very beautiful character. It is not, however, an original product in Toulouse, for the crypt of Canterbury cathedral (1175-1184) affords a similar vault of earlier date and others on a circular plan may be seen in a number of English Chapter Houses.

The Vaulting of Radiating Chapels

As for the radiating chapels, they were added to the ambulatory with the evident purpose of affording more space for altars especially in the great pilgrimage churches.[453] At the beginning of the eleventh century, three such chapels had already been built off the ambulatory of Saint Martin at Tours and only slightly later in date are those in La Couture at Le Mans followed by those of a great number of churches of the eleventh and twelfth centuries.[454] Nor are such chapels found only in churches with ambulatories. They frequently open directly off the apse, sometimes being merely recesses in the thickness of the outer wall[455] but more often extending beyond it.[456] Ordinarily, however, churches with radiating chapels have an ambulatory as well; but even so, there are occasional examples of chapels lying entirely within the thickness of the exterior wall[457] in which cases they are merely half-domed niches.

Whenever these radiating chapels are found there is considerable variance both in their number and ground plan. Sometimes there is but one,[458] sometimes two,[459] in the majority of cases three,[460] very seldom four,[461] but frequently five.[462] In plan, the chapels are generally semicircular with or without one or more preceding rectangular bays.[463] Naturally they are vaulted exactly in the manner used for the principal apse of the church or the minor apses of the transept at the time the chapels were built. The usual Romanesque form is the simple half dome like that in Saint Nicolas at Blois, which is especially interesting because it still retains its painted decoration. As the ribbed half dome came in in apse vaulting it appeared in a number of radiating chapels, at Domont and Saint Martin of Étampes, for example, but the usual Gothic form was the chevet vault which corresponds exactly with that over the major apse, except when it is combined with the ambulatory vault in the manner already described,[464] or is of square,[465] circular, polygonal, or irregular plan.[466] In such cases the vaulting is adapted to the plan without any great structural changes from the types found in the remainder of the church. The cathedral of Auxerre (Fig. 84 and Plate III-f), for example, shows the use of a ten-part vault over a square chapel, while Saint Germain also at Auxerre and Saint Remi at Reims (Fig. 87 Plate III-l) have chapels of almost circular plan covered with a vault which is virtually a double Gothic chevet like that of the transept chapels of Soissons and Laon cathedrals already described. [467]