A Literary and Structural Analysis of the First Dome on Justinian's Hagia Sophia, Constantinople (original) (raw)

T he first dome of Hagia Sophia in Constantinople, perhaps the greatest structural and artistic innovation in Justinian's church, is lost to us forever. Its precise shape and size are not recorded in the written or visual records; nor does an approximation of it survive in architectural filiations. Completed sometime in 537 C.E., the dome lasted just over twenty years before a series of earthquakes in 557 led to the collapse of the eastern main arch in May 558. Deprived of this support, portions of the dome and eastern semidome fell with the arch, and the rest of the dome was cleared away for rebuilding. In his ekphrasis written for the second consecration of the building in 563, Paul the Silentiary describes the collapse this way: Now the wondrous curve of the half-sphere, although resting on powerful foundations, collapsed and threw down the entire precinct of the sacred house.... Yet, the broad-breasted fane did not sink to the foundations... but the curve of the eastern arch slipped off and a portion of the dome was mingled with the dust: part of it lay on the floor, and part-a wonder to behold hung in mid-air as if unsupported .... following describes the dome and the primary structural components supporting it and cites some of the structural movements that have taken place over the years [Figure 2]. Of a broad, rectangular basilican plan, Hagia Sophia is oriented roughly on an east-west axis. The crown of the present dome (A), which is just over 100 Byzantine feet in diameter, hangs 178.3 feet (55.6 m) above the floor.5 Four main piers (B), made mostly of limestone and greenstone ashlars, define the corers of the central 100-foot square of floor that lies beneath the dome. They rise 74.17 feet (23.14 m)6 and are spanned by four thick semicircular arches of brick (C), which are bound together by brick pendentives (D). These culminate at 133 feet (41.5 m) in a somewhat deformed circle of flat marble blocks upon which the dome rests (E). The blocks jut out several feet into the central space, forming a cornice used as an inner walkway around the dome's base. The main east and west arches serve as the terminations of the two main semidomes (F) which, being roughly full quarterspheres, have a slightly smaller surface radius than the main dome. The semidomes extend the nave to nearly its full length, and are each supported by the main piers and two secondary piers toward each end of the nave (G). The semidomes and secondary piers serve as the principal east-west buttresses to the dome, main arches, and main piers.7 To the north and south, 66 JSAH / 55:1, MARCH 1996 L9 VIHdOS VIOVH NO 3hNO(I LSMII :OyIAVI 9b8 1 u! !iessoj addssn! pue a.edseg spaiq!4y. aqT Xq paejua9 se 'e!idoS e!1eH Jo auwop!uuas UJapsea pue awop 1J4uaD aqlI :1 3IEnDJ :>-O < 1 1 FIGURE 2: Isometric cutaway view of Hagia Sophia as it is today (modified from Mainstone, Hagia Sophia). The dome (A) rests upon the cornice (E), which forms a ring at the top of the pendentives (D). The main arches (C) spring from massive stone piers (B), which rise from the corners of the central I 00-foot square. The secondary piers (G) help to support the semidomes (F). Mainstone shows that these latter elements effectively buttress the dome and the east and west main arches. The buttresses to the north and south (H) have been somewhat less successful in countering the lateral thrusts of the dome and main arches. external buttresses (H), rising nearly to the height of the main arch crowns, are joined by arches and walls to the main piers and the superstructure above them. The present dome, parts of which have survived for 1,400 years, rises 48 feet (15.0 m) from the level of the upper cornice, just slightly short of a hemisphere.8 It is made of brick and pozzolanic mortar. Anchored to the cornice, and thus indirectly to the arches, it is pierced at the base by forty arched windows. Between the windows thick radial ribs rise to the crown; the webs, well integrated with the ribs, are somewhat recessed, with an average thickness of about 2 /2 feet.9 On the outside, the ribs broaden into equally spaced spurs extending out about 7 feet, which serve as radial buttresses for the dome. Isidorus the Younger, nephew of one of the original architects, designed the second dome. He decided to demolish the remainder of the first dome and start afresh, attacking the structural problem at the level of the arches. Agathias provides a few interesting facts about the rebuilding: Since Anthemius had long been dead, Isidore the younger and the other engineers reviewed among themselves the former design and, by reference to what had remained, they judged the part that had fallen down, i.e., its nature and its faults. They left the east and west arches as they were in their former places, ? but in the case of the north and south ones they extended inward that part of the construction which lies on a curve and gradually increased its width so as to make them [the north and south arches] agree more closely with the others and observe the harmony of equal sides. In this way they were able to reduce the unevenness of the void and to gain a little on the extent of the space, i.e., that part of it which produced a rectangular figure. Upon these [new] 68 JSAH / 55:1, MARCH 1996 -%I.oe -0