Cambridge Ancient Hi.. - Index of

eligious architecture 963
Juliana. Now destroyed, its substructures and debris (including profuse
exotic sculptural decoration) have been excavated. Its plan and elevation
have been reconstructed as a centralized church with a dome on massive
piers surrounded on four sides by aisles, narthex and sanctuary, all of about
equal widths. On the north and south sides of the central space stood a pair
of two-storey exedrae composed of three niches with a pier in between.
The spaces around the domed bay would have been covered with barrel or
cross-vaults. 73
St Sophia, Constantinople, built in 532–7 to replace the cathedral of
Theodosius II – a timber-roofed basilica dedicated in 415, which was
burned down in the Nika riot – represents a high point in Byzantine technological
achievement (Fig. 59, and Fig. 34, p.904 above). The design of
St Sophia has been described as achieved by splitting Sts Sergius and
Bacchus (Fig. 58) in half and inserting a central dome. 74 St Sophia’s dome
on pendentives, 100 Byzantine feet (31 metres) in diameter, stands 56
metres above floor level. The webs between the forty dome ribs are
pierced by forty windows. The four main and four secondary piers are of
stone up to the springings of the gallery vaults; the four buttress piers are
of stone up to the springing of the aisle vaults. The arches, vaults, semidomes,
pendentives and dome are constructed of brick, while the springing
course of the dome is a cornice of Proconnesian marble. The
monolithic marble columns of the galleries do not stand directly above
those at ground level, but redistribute the vertical loads from above.
When the church was first built, the nearest comparable domed space was
that of the Pantheon in Rome, which was completely centralized, its
hemispherical dome set on a cylindrical base of walls. By contrast, St
Sophia is a complex domed structure which combines the centrality of an
aisled tetraconch with the axiality of a normal basilica. A primary system
of masonry (Fig. 59a), located mainly within the nave, carries the principal
weight load, and secondary systems, mostly within the enveloping
spaces (narthexes, aisles and galleries) support only themselves.
The technological achievement in building St Sophia was, however,
flawed: twenty years after completion its dome collapsed and had to be
rebuilt. Most scholars attribute the collapse of this original dome to its
shallow pitch, which directed its force outwards, creating lateral pressure
against the four main piers. According to Agathias, the new dome was built
taller, and thus its weight is transmitted downwards in a more vertical path,
reducing lateral pressure. However, the dome again collapsed in part in the
tenth and in the fourteenth century, so that the present structure incorporates
several stages of construction, while retaining the profile of the dome
as rebuilt after 557. 75
73 Harrison (1989). 74 Mango, Byzantine Architecture 106–21, 123. 75 Mainstone (1988).
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