How to Study Architecture by Charles H. Caffin (reading the story of the .TXT) 📖

EXTERIOR OF S. MARK’S, VENICE

Showing Gothic Details Imposed on Byzantine Design. P. 209

had dried and settled, the masons and the decorators completed the work, by overlaying the walls, domes, and pediments of the interior with marble or mosaics.

The floors were paved with richly coloured marbles, in opus sectile or opus Alexandrinum. Marble, also, cut in thin veneers and arranged so that their veining produced symmetrical designs, was applied to the walls. Marble, again, but incised with carved ornament, covered the soffits of the arches, the archivolts, and spandrels, while the vaulting was resplendent with mosaics, composed of figures and ornaments, executed in enamelled glass upon a background of gold or blue or, more rarely, pale green.

Colour was pre-eminently the motive of the interior decoration and to this end carved work was subordinated. The ornament was in very low relief, spreading over the surface in intricate patterns, that suggest the delicate enrichment of lace. Mouldings were replaced by bands of mosaic or marble, carved or smooth. The chief motive of the carved ornamentation was the mingling of the acanthus and anthemion. The treatment of both was rather Hellenic than Roman; the foliage having pointed ends; but it was deeply channelled and drilled with deep holes at the springing of the leaves. In fact, the use of the drill as well as the chisel was characteristic of Byzantine carving and emphasises the suggestion of the ornament being raised rather than, as in Roman decoration, applied. Corresponding to the general flatness of the ornament is the constraint of the contours of the mouldings, suggestive of Asiatic languor and in marked contrast to the vigorous profiles of classic architecture. The impression, indeed, of the whole scheme of decoration is rather one of soft richness, as carving melts into colour and colour deepens and glows and finally passes into the gold or depths of azure of the vaulting.

When the supply of antique columns was exhausted the Byzantine architects began to imitate them, but soon departed from the classic type. In certain cases the capital retained something of its derivation from the Ionic or Corinthian styles; but gradually a new type was evolved, which was distinguished by being convex to the outside rather than concave. The motive appears to have been to give additional support to the arch, for which purpose an impost was, as the name implies, “placed upon” the capital. It consists of a block, which projects beyond the edges of the capital to fit the extra thickness of the wall and may represent, as has been suggested, the survival of a part of the architrave of the discarded entablature. In the decoration of the capitals the foliage was sometimes enclosed in frames of interlace, or the latter took the form of a basket, on which birds are perching.

Pendentive Dome.—We have now to consider the most characteristic feature of Byzantine architecture—the Dome. Briefly, in the 200 years that divided Justinian from Constantine the Byzantine architects perfected a principle of dome construction by which they crowned a square plan with the circle of a dome.

The Romans confined their domes to circular or polygonal buildings. Meanwhile they had worked out the construction of groined vaulting upon four supports. The Byzantine achievement was to make four supports carry a dome. It was accomplished by developing the element of construction—the pendentive.

We have already noted the bas-relief found at Koyunjik, which shows that the Assyrians understood the crowning of small square buildings with domes. While actual examples have perished, the tradition of this construction seems to have survived in the East. For in the third century A.D., when the Persians established the Sassanian Empire under the impulse of a movement that sought to restore the ideals and habits of the old national life, the builders erected domes in the palaces of Serbistan and Firuzabad.

The method they adopted was to bridge each angle of the square, at some distance below the top, with a small arch. On these they erected two small arches that projected beyond the face of the original arch and accordingly extended the width of the bridge. They continued this process of superimposing tier upon tier of arches, until the bridge was level with the top of the square, by which time the latter was transformed into an octagon. Then, by inserting a corbel or bracket in each angle of the octagon and taking advantage of the thickness of the masonry, they were able to adjust a dome to the structure. This system of dome-support, we shall find, was adopted in Gothic architecture, where the arches are called squinches.

Another method of dome-support, found in the Mosque of Damascus and frequently employed in the churches of Asia Minor, was to bridge the angle with a semi-circular niche.

Meanwhile what the Byzantine architects developed was a geometrically exact system of converting the square into a circle by means of concave triangular members that are specifically called pendentives.

The character and function of a pendentive may be readily grasped by a practical experiment. Cut an orange into two hemispheres. Lay the flat of one on four reels, placed at the four angles of a square, inscribed within the circle. These reels represent the piers on which the pendentives are to be constructed. Now by four perpendicular incisions of the knife cut off the segments of the hemisphere that project beyond the square. The lateral spaces between the piers will now be spanned by four arches. Finally, a trifle above the top of the arches, make a horizontal cut, removing the upper part of the hemisphere. The rind which remains represents the four pendentives. The flesh inside of it may be likened to the timber centering used in the construction of the pendentives and, now that the latter are completed, may be removed. Remove also the flesh from inside the upper part of the hemisphere. It will then be a hollow cap, which you can replace on the top of the pendentives. You now have an instance of a dome and pendentives included in a single hemisphere. More usually, however, the architect makes the curve of the dome different from that of the pendentives. Frequently, too, to give the dome superior distinction, he constructs a cylindrical wall on the circle of the pendentives, and on this drum, as it is called, elevates his dome.

Scientifically stated: “If a hemisphere be cut by five planes, four perpendicular to its base and bounding a square inscribed therein, and the fifth parallel to the base and tangent to the semi-circular intersection made by the first four, there will remain of the original surface only four triangular spaces bounded by arcs of circles. These are called pendentives.” (Professor Hamlin.)

The first church built by Justinian was SS. Sergius and Bacchus in Constantinople. The part dedicated to the latter saint—a small basilica—was destroyed by the Turks. The remainder presents the plan of a rectangle enclosing an octagon on which rests a dome of a curious, fluted, melon shape.

A few years later was erected the church of S. Vitale in Ravenna, probably as the Court Church. Its plan is an octagon within an octagon; the inner one being surmounted by a dome.

The domical arrangement of both these churches may have been originally derived from the Pantheon, modified by the example in Rome, of what is called the Temple of Minerva Medica, though it was probably a nymphæum. This building is decagonal with niches projecting from nine of the sides, while the tenth provides the entrance. The dome, of concrete ribbed with tiles, is built over an inner decagon of ten piers carrying ten arches. These in turn support a decagonal drum, pierced with windows, the angles at the top being filled in with rudimentary pendentives. The same principle of construction reappears in both S. Sergius and S. Vitale; the dome of the latter being composed, for the sake of lightness, of earthenware, amphora-shaped pots, the bottom of one being fixed in the lip of another. It is sheathed on the outside with a wooden roof.

This Church of S. Vitale became the model on which Charlemagne based his domical church at Aix-la-Chapelle, which was built as a royal tomb, A.D. 796-814, and was afterward used as the crowning-place of the Emperors of the West.

S. Sophia.—Finally, the pendentive system was fully developed in Justinian’s church in Constantinople dedicated to the Holy Wisdom—Hagia Sophia, called, though erroneously, S. Sophia. It marks the highest development of the Byzantine genius for domical construction.

The architects were Anthemius of Tralles and Isidorus of Miletus, who began the work in 532 and finished it in 537. The plan shows four mighty piers, 25 feet square, set at the angles of a square of 107 feet. These support four arches and intermediate pendentives of noble height, the apex of the dome being 175 feet from the pavement. For the original dome, having collapsed in 555, was replaced by a higher one, lighted by the introduction of forty circular-headed windows around the spring of the curve; an arrangement not only excellent in admitting light to the interior, but also as wonderfully impressive in its way as the single eye