The Church of Sancta Sophia, Constantinople: A Study of Byzantine Building

by W. R. Lethaby; Harold Swainson

The arches of seventy-two feet span have abutments of twenty-four and a half feet, which are increased above the vaults of the gynaeceum to twenty-nine feet.

The great arches under the springing of the dome are about four bricks, or five feet, thick. The depth at the top, including the cornice of the dome, is about six feet and three quarters. The centre of the arches is two and a half feet above the springing, so that they are more than semicircular. In the internal angles formed by them are the four pendentives. The cornice has a projection of about two feet nine inches. The lead mentioned by the Silentiary may be found in the interstices of its stones.

The dome springs from the cornice on forty piers, about three feet five inches broad on the inside, and about eight and a half feet deep in the direction of the radius. They are connected by arches which form windows four feet nine inches wide. On the outside the piers project beyond the arches, and may perhaps at one time have been connected with other arches, forming a drum for the dome: within they form part of the ribs of the dome.

In the interior the ribs project at the springing six inches from the surface of the dome, which is there twenty-nine inches thick, but their projection gradually diminishes, till they are lost in the great circle of thirty-seven and a half feet diameter in the centre. In the interior from rib across to rib is 104 feet, so that all round on the cornice is the passage two feet nine inches wide, which, according to Paulus, was used by the lamp-lighter. The dome rises forty-six feet nine inches above this gangway, so that it is considerably less than a semicircle in section. The original dome, according to Agathias, must have been even flatter. Theophanes states the increase in height to have been twenty feet, and Zonaras twenty-five.[253]

The dome has now many swellings and depressions which are not visible from the ground. At the same time we see how immovable domed vaulting is, if only its supports remain uninjured.

At the east and west ends of the nave the two cylindrical vaults are each forty-seven feet across. They rest on the four lesser piers, and have an abutment of fifteen and a half feet. The four exedras are each forty-one feet across. All the conchs and semidomes have drums outside, which are pierced by the windows. The conchs which cover the exedras have strong arches, where they intersect the semidomes. The weight of the exedra conchs is chiefly supported by the columns; the upper columns of the south-east exedra, at the time of the last restoration, were much inclined, and had to be brought back to the vertical, by propping the arches, cutting away the old bases, and inserting new pieces—the columns being surrounded and supported by wooden cradling. The thickness of the western barrel vault is four feet; the eastern apse is about three feet thick. The western semidome received an additional thickness at the restoration.

Vaulting of the Aisles.—The three principal divisions of each aisle are covered by domical vaults. The vault arches rest partly on columns; and the spaces between these columns and the outside wall are also vaulted. The middle division of the north and south aisles has two domical vaults, separated by a barrel vault that opens towards the nave arches, and to the window in the outside wall. The arches have iron ties four inches thick, which stretch from the outer wall to the columns of the nave, and grip them tightly. The four columns in the aisles which carry the vault are much lower than those between the aisles and nave, and for this reason the narrow vaulted space, which joins the aisle vault to the nave arcade, is formed by a stilted quadrant.

This arrangement only applies to the lower aisles: above is a stilted cylindrical vault, running lengthways between the main gynaeceum vaults, and the arcade towards the nave.[254] Here, besides the iron ties, there are wooden beams.

The large arches in the aisles are twenty-nine and a half feet from column to column. The domical vaulting of the aisles is very flat—a combination of cross groining and a dome. For, though it starts with angles at the four corners, it gradually merges into a dome at the apex. The vaulting bricks are arranged in horizontal circles.[255] A diagonal band of mosaic starts from each corner, and merges into a central circle.[256] In the gynaeceum the vaulting is higher and consists of spherical domes, the radii being half the diagonals of the spaces covered. The mosaic decoration here again follows the form.[257]

Narthex.—The narthex is covered with vaults, similar to those of the lower aisles of the nave. Each vaulted space is separated from the next by a segmental arch, six and a half feet wide with a span of twenty-six and a half feet, which abuts on the west wall of the nave, and the piers of the outer wall. The vault spaces vary from sixteen and a half feet in the middle to thirteen and a half feet towards the ends. The piers of the outer wall are connected together by arches above the window openings, and the spaces below the windows are filled up with thin ‘screen’ walls. The upper floor of the narthex is covered with a semicircular vault, intersected by the window arches between the piers of the outer wall. These piers are the continuation of those beneath, and have a width of six feet, and a depth of seven. They had to bear the thrust of the barrel vault of twenty-six and a half feet span: the buttresses previously mentioned, springing from the piers of the propylaeum, were subsequently added to strengthen them.