The next step beyond this was a very important one as to beauty of effect. I refer to the practice of drawing the circle by means of a moulding on the surface of the dome, touching the crowns of the arches. This is not only ornamental, but it has the effect of emphasising the first completed course of stones, and perhaps even of strengthening it, and it has the further effect of defining the spherical triangles between the arches which, when thus gifted with a separate existence, receive the name of “pendentives,” whence this entire class of domes are called “pendentive domes.” The earliest specimen of this is probably the little tomb in the Via Nomentana near Rome (Fig. 412), which, though probably of earlier date than the church of SS. Nasario and Celso, carries out the pendentive principle to its full development, just as we see it treated at a later period in the double gate (Fig. 413) and the golden gate of the Temple Area at Jerusalem, most probably erected under Justinian. All these domes are segmental in section.

The pure form, however, of a pendentive dome—that is to say, the form in which the pendentives and the upper portion are really veritable parts of one and the same original dome, in the plan or base of which the rectilinear figure is inscribed—was not long adhered to. It was soon felt that the disc enclosed by the circular moulding looked flat and ineffective; and the idea early suggested itself of converting the circular moulding into a massive cornice, raising upon it a new dome of such proportions as should approve themselves to the eye, and allowing nought but the pendentives to remain of the original dome (Figs. 414, 415).

No bolder idea was ever introduced in constructive architecture; for now the dome, instead of being, as at the Pantheon, supported firmly by a solid wall throughout every portion of its circumference, finds its conditions absolutely reversed; for in no portion of its circumference has it now a solid support, but all floats upon vacuity, suggesting the poetical similitude to Procopius that the Dome of St. Sophia appeared as if suspended by a chain from heaven.

Pendentive domes, in neither of their typical forms, seem to have been frequently or customarily made use of in the more genuine Classic ages, though in modern times they have both been very wisely adopted into the revived Classic styles. They were, in fact, the special characteristic and the great glory of the Byzantine style.

Mr. Freeman, on this subject, remarks:—“The offspring of the arch is the vault, of the vault the cupola; and this majestic ornament is the very life and soul of Byzantine architecture, to which every other feature is subordinate. Its use had hitherto been mainly confined to circular buildings. To make it the central point of a Christian temple was a grand and bold idea, and one which involved a complete revolution in the existing principles of architecture.... And not only did the grand cupola crown the whole pile, but the smaller portions are often covered with smaller domes and semi-domes.... The eye, habituated to the long naves ... of our own great churches, is totally bewildered with so huge a pile, with apses and semi-domes ‘sprouting out,’ to use the expression of Mr. Hope, in every direction, and all circling round the vast central cupola, like tributary rulers encircling an imperial throne.”

It is thought by some that the Byzantines borrowed the pendentive dome from Persia, but this seems insusceptible of proof; indeed, it exists of earlier age in Italy. It is more certain that having once discovered its wonderful utility, it was communicated by them to every region to which their influence extended, and that, having been learned from them by the Mahometans, it became the conspicuous feature of the architecture which extended continuously from the Bay of Bengal to the Atlantic.

The next development I will mention is the raising of the dome proper upon a drum or circular wall, elevated upon the pendentives or corbels, so as to convert it into a species of tower. This seems to have been the first step by which, in later times, the dome came to be made a conspicuous external feature, though rather at the sacrifice of internal beauty (Figs. 416, 417).

It is, in fact, the weakest point in the dome, æsthetically considered, that the same dome cannot be made artistically perfect both within and without. If its height be limited to what looks thoroughly well from within, it is so low in its external aspect as to have little artistic value; while, if raised so high as to be an important external feature, it is only seen by a painful effort from within. This is manifest even in the rotunda, where the dome rises from a circular wall, as in the Pantheon and the Temple of Minerva Medica; but it becomes much more so in a pendentive dome, where the angles are externally encumbered with large masses of masonry. In the earlier Byzantine buildings we accordingly find the dome to have been viewed almost solely as an internal feature, and its exterior very much neglected, and in the case of St. Sophia itself no one would be prepared by its low, heavy, external aspect for the unrivalled glories of its interior. Many of the old architects, in fact, gave up the external form altogether, covering over the dome, as at Parma, etc., by an ordinary sloping roof.

The change I have last chronicled,—the interposition of a circular wall between the pendentives and the dome,—though by no means in all cases leading to the result I am referring to, was unquestionably the origin of the treatment of the dome as an important external feature. It was, in fact, the elevation of the rotunda upon the top of the pendentives. Unhappily, however, it had at once the effect of lifting up the dome above the level favourable to its internal effect, while, if erected on four arches only, the weight became so serious as usually to limit its use to domes of very moderate sizes.

A large number of domes thus raised high above their pendentives or corbellings are really of a class whose claims to the name of dome are somewhat ambiguous. I refer to those whose horizontal section is not circular, but polygonal (Figs. 418, 419). Strictly speaking, this is a variety of groined vault; it is generated by the intersection of several barrel-vaults, springing from the horizontal tops of the surrounding walls. Now, my definition of a dome was a vault generated by the revolution of an arch on its vertical axis. If this were an exhaustive definition, it would follow that the vaults under consideration are no domes at all; yet they look so much like them, and as the number of the sides of the polygon increases, actually approach so closely to the genuine dome, that it would be affectation to deny them the name. They may form the covering of any rectilinear figure at all approaching to regularity of form; as the triangle, the square, the canted square, polygons, either regular or elongated, oblongs or parallelograms of any kind; but the usual form is the octagon or other polygon, and for our general purpose it may be best to limit them to figures capable of being inscribed in a circle or an ellipse.

I have introduced this variety of dome as occurring in those which are raised high above their pendentives or corbels. They occur, however, in numerous positions. The greatest I know of is that of the Cathedral at Florence, of which I shall have to speak more in detail in my next lecture.

But to return to the Pendentive Dome. The Pendentive Dome, though occasionally used at an earlier period, established itself as the leading feature of a style about the time of the Emperor Justinian, and its central seat was Constantinople. The earliest, or about the earliest, church now remaining in that city, seems to be that of SS. Sergius and Bacchus (Figs. 420, 421). Its dome is supported by an octagon. It appears itself to be conchoidal in its horizontal section, and to be supported on sixteen small pendentives. It bears considerable resemblance to the Temple of Minerva Medica, but is really less developed than the baptistery at Ravenna, which dates full half a century earlier.

Contemporary with this was the Church of the Apostles, also erected by Justinian, but now destroyed. It showed, however, according to the description of it by Procopius, an immense advance upon that last named; for, while in one the dome was carried by an octagonal wall, thus showing no practical advance upon the antique form of dome, in the latter a vast cruciform building was covered by five domes, which is just the advantage which the pendentive system affords; for, when the base of a dome is cut into a square by four arches, those arches may aid in the support of other domes beyond, and thus any space may be covered over by a series or a group of domes. This last church, then, was the true type of advanced domical structure.

The great glory, however, of this age, and of domical structure of this class (for it has never again been equalled), is the Church of St. Sophia, or of Sacred Wisdom, erected by the same Emperor as the Metropolitan or Patriarchal Cathedral of the Eastern Church. The plan of this church differs in ideal, and yet more in fact, from the contemporary church last referred to.

The ideal of each is a cross with a central dome. The difference is that in the Church of the Apostles the limbs of the cross were each covered by a complete dome of equal dimensions with the central one (Fig. 422), while those of St. Sophia are covered each by a semi-dome only of equal diameter with the arches carrying the central dome (Fig. 423); so that if we consider the latter to spring from the top of its pendentives, which it in effect does, its springing is on a level with the crown of the surrounding semi-domes.

In reality, however, this idea is not carried out to completion, as only two of the semi-domes have been erected, the other two arches of the central dome being filled in with an arcade in many storeys. This incompleteness, however, is greatly more than compensated—firstly, by the vastness of the scale—the central dome, if measured on the diagonal, being 150 feet in diameter—and, secondly, by other semi-domical projections branching out from the walls which support the great semi-domes, three from each, excepting that on the western side, one is devoted to the entrance, and is not domed. Even these secondary projections are mostly arcaded, so as to allow the eye to pass onward into a yet inner chamber (Fig. 424). So that, simple as is the primary ideal, the actual effect is one of great intricacy and of continuous gradation of parts, from the arcades last alluded to, up to the stupendous dome which hangs with little apparent support, like a vast bubble, over the centre, or, as Procopius, who witnessed its erection, described it, “as if suspended by a chain from heaven.”

The dome is lighted by forty small windows, which pierce it immediately above the cornice which crowns its pendentives, and which, by subdividing its lower part into narrow piers, increases the feeling of its being supported by its own buoyancy.

The interior thus generated, covered almost wholly by domes, or portions of them, each rising in succession higher and higher towards this floating hemisphere in the centre, and so arranged that one shall open out the view towards the others, and that nearly the entire system of vaulting may be viewed at a single glance, appears to me to be, in some respects, the noblest which has ever been designed, as it was certainly the most daring which, up to that time at least, if not absolutely, had ever been constructed.

Its beauties are of a contrary kind to those of that noblest interior of antiquity—the Great Hall of Karnac—or to those of later ages—the Gothic cathedrals. Both of these gain beauty of effect and an increase of apparent extent through the endless intricacies of their perspective, and the changes of aspect at every step arising from the multitude of their columns, and from no possible view showing the whole interior at once. This, on the contrary, trusts to the very reverse of all this—the absence of interruptions and the studious distribution of parts, so that no one conceals another, but that the entire building shall be grasped at once by the eye (Fig. 425).

I have not seen St. Sophia’s, though I long to do so, if only to view a form of artistic treatment so different from what I delight in in our own cathedrals. The internal effect does not, however, trust exclusively to this panoptical theory. The contrary theory was too well known from the Christian basilicæ to be lost sight of in this, the greatest of Christian

temples. It was, in point of fact, added to the other by means of arcades, both in the sides of the nave and in its apsidal projections, opening out mysterious perspectives into the inner recesses of the temple. This union of the more palpable with the more mysterious, of the vast unbroken expanse with the intricately broken perspective, must, as it appears to me, and as I judge from representations, produce an impression more astounding than that of almost any other building; but, when we consider the whole as clothed with the richest beauties of surface; its piers encrusted with inlaid marbles of every hue, its arcades of marble gorgeously carved, its domes and vaultings resplendent with gold mosaic interspersed with solemn figures, and its wide-spreading floors, rich with marble tesselation, over which the buoyant dome floats, self-supported, and seems to sail over you as you move—I cannot conceive of anything more astonishing, more solemn, and more magnificent. Well might its Imperial founder exclaim, when, with pardonable exultation, he viewed the result of his costly aspirations—“Glory be to God, who hath thought me worthy to accomplish so great a work; I have vanquished thee, O Solomon!”

I have dwelt longer on my description of this wonderful building because it is facile princeps among structures on the pendentive domical principle, just as the Pantheon had been among those with the simple dome; and as, in after ages, was St. Peter’s among those whose domes soared upwards as lofty towers.

I must here close my lecture, leaving the continuation of my descriptive sketch of the history of the Cupola, and such remarks as I may have to offer on its uses, its practical application, and its future development, to be followed up in my next.

LECTURE XVII.

The Transition.

Among those remaining at Constantinople, that of St. Irene (Fig. 426) perhaps comes next in date. Its central dome, like that of St. Sophia (Fig. 427), is flanked by arcaded aisles, which, however, do not extend to the vaulting, but simply carry galleries. These wings, therefore, as well as the eastward extension, are covered by barrel vaults, the latter being terminated by a semi-domical apse—while westward is a second dome, like the central one in plan, excepting that, being less in dimension east and west, its base is an ellipse instead of a circle. The actual domes, however, differ much more widely; for, while the western one is a flat disc continuing the surface of its pendentives, the central dome is raised above them on a high drum pierced like a clerestory with many windows.

The Church of the Holy Theotokos, or of the Mother of God, is of much later date. The church proper has but a single dome of any importance, though there are several others over the narthex (Fig. 428). This dome covers the intersection of two barrel-vaults, is supported simply on four columns, and rises high above its pendentives on a drum pierced by windows (Fig. 429). The architecture of this church is very elegant, differing in date, it is probable, but little from that at St. Mark’s at Venice. Others do not differ sufficiently from these types to make it worth while here to describe them. It may, however, be mentioned that in the later Greek churches the domes, or some of them, rose often so high as to become rather elegant towers, arcaded externally. This is the case with several of the churches at Athens.

Among the churches of that city we find one type of great elegance, the Church of St. Nicodemus (Fig. 430), in which the dome occupies the width of what we should call the nave and its aisles; each side of the square over which it stands being divided into three unequal arches, over which it rises on a lofty drum, and is carried on eight pendentives. This forms a most elegant interior, susceptible of many varieties; and, from the spacious central space which it affords, seems the most valuable type on which to found a domed design for a modern church.

It would, however, be endless to enumerate the varied forms of domed churches in the East, though, with all their varieties, they may usually be reduced to a few elementary types. If you desire to study them, I would recommend to you Salzenberg’s Old Christian Architecture at Constantinople, Couchaud’s Byzantine Churches in Greece, and Texier and Pullan’s Byzantine Architecture.

It is not, however, in the East alone, that the Byzantine dome is to be found, even in its earliest days—those

of Justinian himself. It established itself equally at Ravenna; indeed, as we have seen in the baptistery there, as well as in the tomb of Galla Placidia, it, in an early form, preceded those at Constantinople itself. Its great effort, however, there, was the Church of San Vitale, erected by Justinian and Theodora (Fig. 431). This church was evidently imitated more or less from the Temple of Minerva Medica, though whether directly or through that of SS. Sergius and Bacchus at Constantinople can hardly be judged. It is a grand octagon, with a spacious surrounding aisle of double height (Fig. 432). Seven of its sides have the same circular niches projecting from them that we find in the temple (as well as in the Church of SS. Sergius and Bacchus), only they are arcaded and carried out with purely Byzantine details. The aisles are of two storeys, united behind a lofty arcade. This is surmounted by a clerestory, encroaching to a certain degree upon the dome. This, however, is not pendentive. It is covered externally by a roof. It has undergone much modernisation, but retains its general form and a good deal of its ancient decorations, which show it to have been treated much as St. Sophia, with which it was contemporary. The church is the more interesting from having been the type followed three centuries later by Charlemagne in his famous church at Aix-la-Chapelle (Fig. 433).

The manner in which the dome was introduced and adopted in Italy during these ages, was so diverse in its results as to cause it to be very perplexing to chronicle it in any clear consecutive order. There were, in fact, two distinct influences, both occasionally leading to its adoption.

At Rome, and in places under Roman influence, such examples as the Pantheon could not fail to have their effect on the subsequent architecture, and we accordingly find there numerous scions of this primeval family, while, as we have just seen, the purely Byzantine form was simultaneously introduced by way of Ravenna, and later on was planted at Venice.

Through this twofold influence the dome became very frequent throughout Italy. It was carried, as we have seen, by Charles the Great, from Ravenna to Aix-la-Chapelle, and, later on, was carried forward from Lombardy, under the first three Othos, across the Alps, down the valley of the Rhine, and far into the interior of Germany. Only a few years later it was conveyed from Venice into the interior of the south-west of France, whence it spread throughout an extensive district stretching eastward into Auvergne, and even as far as Lyons, and northward to the banks of the Loire, where, to this day, the effigies of our early Plantagenet kings lie beneath a series of pendentive domes almost as perfect as if at Constantinople.

I will not dwell at much length on the domes which were derived from purely Roman traditions, because they, for the most part, suggest no new type or development.

The most magnificent, probably, is that of the Baptistery at Florence, a noble work of early, though unknown, date. It is clearly founded in a great degree upon the Pantheon, though of octagonal plan, and with a dome of the same form (Fig. 434). Its sides are in two storeys—the first with deeply-recessed colonnades on each side—the upper stage a clerestory. One face, however, is occupied by the arch of the sanctuary (Fig. 435).

The dome had formerly an eye, like the Pantheon, but has now a lantern turret. It is encrusted with beautiful mosaic work, with an infinity of figures, the side over the sanctuary having a colossal figure of our Lord in Majesty in a vesica. The architecture is of marble, and the pavement is tesselated work. The whole internal effect is beautiful and impressive in the extreme.

A parallel work is the Baptistery at Parma, a work of the twelfth century. It is polygonal in plan, and greatly inferior to that of Florence (Figs. 436, 437). The church of San Tomaso in Limine, near Bejamo, is simply like an ordinary Templars’ church, with a hemispherical dome over its clerestory, and a turret rising from its apex. San Stephano, at Bologna, is in some degree on the same type.

The greater part of the Italian domes of these periods and of this class, simply cover the crossing or the central tower of a cruciform church, and exhibit no important development.

The most original, perhaps, is the dome of the cathedral at Sienna, which stands upon six piers, forming a hexagon, each side of which is equal in width to the nave and choir (Fig. 438). In the next stage, the angles are corbelled-out, so as to form in the upper storey a dodecagon, which form is followed out in the dome.

The merit of this plan is that it unites itself, with little obstructiveness, with the church on all sides of it, and opens out in its centre a space of double the width of the nave. It is also pleasing and elegant in its effect. But it is time that we returned to the Byzantine type, which you will remember that we left at Ravenna to follow out this digression.

We now adjourn from Ravenna to Venice.

The mercantile and perhaps political connections of the old Venetians were mainly Oriental. This probably accounts for their architecture, up to the twelfth century being Byzantine.

The Church of St. Mark, or the Chapel of the Doge’s Palace, was founded in the ninth century, in honour and for the reception of the body of St. Mark, which had been procured from Alexandria, when the church in which it had been long deposited was destroyed by the Moslems. This church, however, perished in a popular tumult, late in the tenth century, whereupon the Venetians set about its reconstruction with a determination to render it one of the finest and most sumptuous in existence (Fig. 439). All the East, so far as accessible to their ships, was laid under contribution for columns and other architectural embellishments. The design is often spoken of as founded on that of St. Sophia. This was not the case. The Church of the Apostles at Constantinople would rather seem to have furnished its model.[64] It consists of a group of five square spaces, covered each by its pendentive dome. Its peculiarity lies in the breadth of the strips of wagon-vault which support and separate these domes, which is so great that the vast piers which sustain them are pierced in two storeys, and divide each other into four piers, with a vaulted space between them. Each dome is consequently the centre of a cruciform space, the wings of which have wagon-vaults. The only exception is the east end, where an apse is substituted for this space, and out of this apse spring three minor ones, as at St. Sophia. Each dome is about hemispherical above its pendentives, and is pierced with windows, as at St. Sophia.

The domes are now, and have been for many ages, covered over by lofty domical towers of timber, each surmounted by a sort of turret on its apex (Fig. 440). The wings which flanked each domed space, bounded as they were by the perforated piers, were so suggestive of side aisles that the builders, familiar, no doubt, with aisled churches, added arcades from pier to pier, both in the nave and transepts. These, however, are merely decorative, supporting no galleries, as is frequent in the East, and only serving as narrow communications, equivalent to triforium passages, between the upper chambers in the great piers.

The entire church is internally encrusted with richly-coloured marbles and gold mosaic, with figures, just as at St. Sophia’s;[65] and the floor is of marble and porphyry tesselation, varying in scale from the most vast slabs to the finest mosaic work.

The interior was, no doubt, a joint imitation of St. Sophia’s and the Apostles’ Church, rivalling the former in its sumptuous decoration, and imitating the latter in its plan.

To those who have not visited the East, this interior gives a very faithful idea of the splendour of a Byzantine church, and I must say that I have myself seen nothing more impressive (Fig. 441).

I will only further (before proceeding to another branch of my subject) notice one other church—the little church of Santa Fosca (Fig. 442), on the island of Torcello, close to Venice. This church is not domed, or has only a wooden dome, but was clearly planned for a proper domical covering. Its plan is like that of St. Nicodemus, at Athens,[66] already alluded to, and is perhaps one of the most beautiful in existence, and one best adapted of all domical arrangements to modern use. Before I proceed farther I must call your attention to a fresh step in advance.

The next step in the development of domes is the adoption of pointed arches for their support, often accompanied by an increase in the height of their own section beyond that of a semicircle.

The fact that the pendentive dome is, as it were, suspended in mid-air, so that a perpendicular line dropped from any part of its circumference passes through empty space, renders it imperative that the arches which sustain it in this airy position should be extremely strong, and should have as little outward thrust as possible; and it is equally desirable that the courses of stone forming the pendentives should not form very acute angles with the haunches of these arches. These considerations seem to have led the Mahometan architects soon to substitute pointed arches for round as the supports of their domes; a step in which they were followed at a later period by the greater part of those Western European architects who adopted the pendentive dome. There can be no doubt that this was a very advantageous change. Mr. Fergusson says: “A little reflection ... will show how difficult it is to adapt the curves of a pendentive dome to a circular arch, and how weak the arrangement is when done.... With a pointed arch, however, even when the pendentives follow its lines, there is some thickness in every part, and no curve need slope forward at a greater angle than 45 degrees.”

On the other hand, the change was attended with the loss of geometrical accuracy. Hitherto we have dealt with none but perfectly correct geometrical figures; but the moment the pointed arch is introduced, the pendentives lose this exactitude, and have to be adapted by what is vulgarly called “rule of thumb” to conditions not precisely suited to their forms. A pendentive between pointed arches has, it is true, a geometrical form of its own, but this is so awkward in its sections that it has only to be seen to be rejected; for, instead of its central section being a regular arched curve, suited to a domical surface, it is a curve of double flexure, its lower part concave (as seen from within), and its upper part convex—in short, an ogee. This being inadmissible, the curve has to be accommodated the best way we can, so as to avoid this weak and unpleasing form. We have, in fact, to determine, according to the best of our judgment, what shall be the vertical section of the pendentive, and adopt such horizontal curves for the courses of masonry as will make it reach the extrados of the supporting arches in the easiest manner we are able. This was really done so successfully by the French architects, whose works I shall shortly have to describe, that, for myself, I must say I never found out the difficulty from seeing them, and was unaware of it till I worked out the profiles geometrically.

After all, however, it is only parallel to what we have to do in filling in the spaces between the ribs of Gothic vaulting.

The pointed arch, though beautiful and practically excellent, is no regular geometrical figure, but the union of portions of two; its use, consequently, induces irregularities which would be at once avoided by the substitution of an ellipse. But then our geometrical accuracy would be purchased by the sacrifice of beauty.

All the sections of a sphere being circles, the supporting arches of a true pendentive hemispherical dome are semicircular arches, and in the same manner those of an elliptical spheroidal dome would be semi-ellipses; but there is no regular solid figure, more than one of whose sections are pointed arches, so it is natural that when they are used some part should have to be accommodated to fit them.

It may, however, be as well at this point to mention that pendentives, after all, had become mere rudiments of a form which had lost its original intent. Ever since the dome ceased to have the same curvature with its pendentives, and to be a continuation of their surface, the latter had become a mere form of corbel, for which any other variety might at convenience be substituted. This fact was amply acknowledged in every region where the dome was made use of; so that from the pillars of Hercules to the Bay of Bengal, and among those who occasionally adopted and developed upon Byzantine ideas in Western Europe, we find all forms of corbelling used in addition to the typical pendentive. I shall presently have to show you some of these varieties, and will only now remark that, though they are perfectly legitimate means of support, the pendentive has still the advantage of them in its simplicity and in its superior adaptation to coloured decoration.

About the beginning of the eleventh century, the Byzantine style, in all its integrity (excepting only in its richer decorations), was conveyed into Aquitaine, as it is supposed, by Venetian merchants, who at that time had extensive commercial establishments in that part of France.

The earliest work carried out under this semi-Byzantine influence was, so far as we know, the church of St. Front, at Perigueux (Fig. 443), a building obviously copied from St. Mark’s, at Venice.[67] The two churches are, in fact, nearly identical in their plans and sections, the one being an almost unadorned copy of the other, showing us what St. Mark’s would be if stripped of its marble encrustations and its mosaics.