nople; but it is
certain that, to attain the power of designing and erecting so great a
work as Santa Sophia, the architects of Constantinople must have
continued and largely modified the Roman practice of building vaults
and domes. There is every probability that if some of the early
churches in Byzantium were domed structures others may have been
vaulted basilicas; the more so as the very ancient churches in Syria,
which owed their origin to Byzantium rather than to Rome, are most of
them of the basilica type.

[Illustration: FIG. 159.--CHURCH OF SANTA SOPHIA AT CONSTANTINOPLE.
LONG SECTION. BUILT UNDER JUSTINIAN BY ANTHEMIOS AND ISIDOROS.
COMPLETED A.D. 537.]

A church which had been erected by Constantine, dedicated to Santa
Sophia (holy wisdom), was burnt early in the reign of Justinian (A.D.
527 to 565); and in rebuilding it his architects, Anthemios of
Thralles, and Isidoros of Miletus, succeeded in erecting one of the
most famous buildings of the world, and one which is the typical and
central embodiment of a distinct and very strongly marked
well-defined style. The basis of this style may be said to be the
adoption of the dome, in preference to the vault or the timber roof,
as the covering of the space enclosed within the walls; with the
result that the general disposition of the plan is circular or square,
rather than oblong, and that the structure recalls the Pantheon more
than the great Hall of the Thermae of Diocletian, or the Basilica of
St. Paul. In Santa Sophia one vast flattish dome dominates the central
space. This dome is circular in plan, and the space over which it is
placed is a square, the sides of which are occupied by four massive
semicircular arches of 100 ft. span each, springing from four vast
piers, one at each of the four corners. The four triangular spaces
between the corners of the square so enclosed and the circle or ring
resting upon it are filled by what are termed "pendentives"--features
which may, perhaps, be best described as portions of a dome, each just
sufficient to fit into one corner of the square, and the four uniting
at their upper margin to form a ring. From this ring springs the main
dome. It rises to a height of 46 ft., and is 107 ft. in clear
diameter. East and west of the main dome are two half-domes, each
springing from a wall apsidal (_i.e._ semicircular) in plan. Smaller
apses again, domed over at a lower level, are introduced, and vaulted
aisles two