1. The builders and the original function of the church

Sts. Sergios and Bakchos or Sergius and Bacchus (today Küçük Ayasofya Camii), located on the Marmara shore of the First Hill, just inside the wall circle and south-west of the impressive substructures of the south curved end of the hippodrome, is one of the most important surviving monuments of the early Byzantine period. The church was built by Justinian I (527-565) and his wife Theodora in the Hormisdas Palace that was their private residence before Justinian became the emperor. An impressive dedicatory inscription, carved around the nave in the rich entablature, name the royal patrons.¹ The capitals also bear the monograms of Justinian and Theodora, though no cruciform monograms have been found, which should indicate an early date, but no earlier than 527, since Theodora's name is also attested. The evidence, therefore, date the monument to the period 527-533, more likely 530-533.²

Despite its location inside the palace complex, the church of Sts. Sergios and Bakchos cannot be regarded as a palace chapel, because it was built to serve the Monophysite community that was housed in the Hormisdas at time when the imperial couple had already moved from there to the Imperial Palace (in 527).³ Monophysites claiming that Christ has only one nature were taken as heretics by the Orthodox church that teaches that Christ has two natures, one divine and one human. Nevertheless, they were favoured by the Empress Theodora, which explains why they were allowed to use the Hormisdas Palace as a shelter and were given such a magnificent church. The situation changed after Theodora´s death, as Justinian preferred Orthodoxy and he moved the community elsewhere.

2. Neighbouring palace church of Sts. Peter and Paul

The church shared, in the early Byzantine period, a narthex and atrium with Sts. Peter and Paul.⁴ The latter was the palace chapel of Justinian´s Hormisdas Palace and was probably situated to the north of Sts. Sergios and Bakchos, because the excavations along the south façade carried out during the restoration of the building in 2004 did not reveal any remains of a structure that could be identified as the church of Sts. Peter and Paul.⁵ The dedication of Justinian´s church in his private residence to Sts. Peter and Paul appears to have been motivated by the reconciliation of Justin I, Justinian´s uncle, with the papacy, thus ending the Acacian schism.⁶ Moreover, Justinian apparently asked in 519 the Pope Hormisdas for sending relics of the two apostles and St. Lawrence for his new palace church.⁷ Unlike slightly later Sts. Sergios and Bakchos, Sts. Peter and Paul was built in the traditional manner as a basilica with straight rows of columns dividing its interior in aisles, thus similar to the early churches of Constantinople (Theotokos in Chalkoprateia, St. John Stoudios).

Sts. Peter and Paul was abandoned probably soon after the 6^th century, but Sts. Sergios and Bakchos became the centre of a monastery of the same name till the late Byzantine period.⁸ The Book of Ceremonies informs us that a corridor connected the church with the Palace so that the emperors could go directly from their residence to the gallery of the church.⁹

3. Architecture of the church of Sts. Sergios and Bakchos

The church of Sts. Sergios and Bakchos is externally rectangular and internally octagonal in plan and is covered with a large dome. It shares its closest structural parallels with three churches erected also in the Justinianic period: S. Vitale in Ravenna, St. John the Baptist in Hebdomon (modern Bakirköy, part of Istanbul) and Archangel Michael in Anaplous (on the European shore of Bosphorus, modern Arnavutköy).¹⁰ The domed octagonal nave is outlined by a continuous gallery on two floors, which envelops the nave to the north, west and south. The nave dome, which is composed of sixteen ribs with eight windows, is supported on eight wide arches that fall on eight heavy piers forming an octagon. The space between the piers is spanned by twenty-eight marble columns, two in each bay with the exception of the bema. The upper gallery columns are interlaced with small arches whereas the columns in lower colonnades carry an architrave. Columns at the four corners of the nave are arranged to form semi-circular niches that are crowned with semi-domes at the upper gallery level. To the west, the gallery joins a double-story narthex, separated only by a series of columns and piers. According to a recent research, the narthex is a later addition¹¹ (but it probably dates also to the sixth century as can be judged from its pure brick masonry).

Triple arched windows provided originally light for the enveloping galleries on both levels. Only the lower triple window in the middle of the south Justinianic wall of the church is still almost intact. Its columns show that window frames were once attached to them. Columns and capitals of the south upper triple window were replaced in the Byzantine period but the original appearance of that part of the upper gallery has not changed much since the sixth century (but it has changed profoundly on the exterior of the south flank – see below). On the other hand, triple windows in the north wall have almost disappeared. The upper north triple window is no longer visible from the interior of the church but its remnants can be recognized on the facade. The same could be also said until recently about the lower north triple window. However, the restoration of the building, which was finished in 2006, uncovered parts of columns belonging to it. During the mentioned restoration work a Byzantine-period marble floor was found in the south-east corner of the church. It has been decided to leave it visible for the visitors and is covered only with glass.

As mentioned above, the south side of the church underwent profound changes in the Byzantine period. The south flank of the building is composed of two parallel, interconnected walls. The inner wall belongs to the original Justinianic church. The outer wall, part of which are massive buttress piers connecting the two south walls, was built later than the main body of the church, possibly between the 7^th and 10^th century on the basis of the masonry (it shows alternating bands of brick and stone while the Justinianic church has pure brick masonry). The facade is articulated by three broad brick arches at the groundfloor level (originally part of an arcade, now blocked) to which smaller arches at the gallery level (only fragmentary remnants of which survive) are centred. Sts. Sergios and Bakchos was reconstructed by Basil I (867-886) (perhaps after the earthquake of 869) and this indicates that the outer south wall may have been built during his reign.¹²

4. Evaluation

The Church of Sts Sergios and Bakchos is a fine example of the inventiveness of architects and designers in the years of Justinian I. The principle of the architectural design compares with that of Hagia Sophia of Constantinople, in that it proposes a similar method of transition from the outer quarter shell to the trilevel domed core, which is here octagonal. The volumes interpenetrate as the center space loses its clarity and expands into the niches, and from the niches out into the enveloping spatial shell. The execution of the church's highly sophisticated scheme is rather ambivalent, probably due to the constraints of empirical building practice at the time; thus the seemingly regular octagon actually has sides of different length, the arches are rather clumsy and the proportions are somewhat low, while the irregularity of the site has complicated the adaption of the ambitious planning on it. But the overall impression is that of a sophisticated exemple of the architectural development of this period, with its innovative molding of space and manipulation of light. The refined sculptural decoration, with its dynamic forms and sharp contrasts of shadow and light, the result of the ample use of the drill, certainly add to the general impression. These elements will appear on a vastly enlarged scale in Justinian's Great Church, Hagia Sophia, in spite of the two monuments' many differences in planning and architectural solutions. San Vitale in Ravenna is another variant, slightly simplified but more masterly applied, of the subtle planning seen in Sts Sergios and Bakchos. Such imperial commissions «represent an architecture developed to appeal to the discriminating taste of the 6^th-century elite».¹³