Architecture

The Church of Saints Sergius and Bacchus was built by Justinian and Theodora within the Hormisdas Palace complex. It was connected to the earlier Justinianic church of Saints Peter and Paul, with which it shared a narthex. While it has been called the city’s oldest functioning religious institution with the oldest dome, there has been considerable debate about the date, design, and circumstances of its construction.

Sts. Sergius and Bacchus is a double-shelled structure, as the exterior structure masks the interior plan. While the former church is not so large, it is designed in such a way that produces a sense of spaciousness inside. It has a domed octagonal central core with an irregular rectangular exterior. This central core is rotated at an angle in relation to the exterior walls. It is generally believed that it was flanked by the Palace of Hormisdas and Sts. Peter and Paul on its north and south sides. While they have long since disappeared, these earlier structures are likely the reason that Sts. Sergius and Bacchus has a curious external form, which was not originally intended to be visible. It could also mean that its lopsided plan was skillfully executed within the limits of an irregular space.

The irregular square plan measures less than 30 m², while the length from the narthex to the apse is a little over 38 m. Its masonry consists of bricks with thick beds of mortar and occasion bands of stone. Its apse, which has three large windows with brick arches, is semicircular internally and three-sided externally. The octagonal core has eight wedge-shaped piers supporting a sixteen-sided dome. Its dome, which is over 30 m high, has a diameter of around 16 m. A long sanctuary bay with an apse projects to the east in the eighth recess. Between its eight piers are alternating rectangular and semicircular exedras with alternating pairs of marble columns. The octagonal core is enveloped by an irregular ambulatory with semicircular niches diagonally placed in the interior four corners. A similar plan can also be found at the gallery level. Eight arches, which spring from the eight piers at the gallery level, support its segmented “pumpkin” dome. There are also alternating pairs of columns at the gallery level. The sixteen sides of the dome alternate between concave and flatter sides. The concave sides rest on the piers, while the flatter sides have a total of eight windows. The dome also has a series of elaborate buttresses. While it is often considered its original sixth-century dome, it has been argued that the dome was built during the ninth-century repairs of Basil I or even later during the Ottoman era. This is partly based on the evidence of high truncated arches that are now plastered over. Recently, it was even proposed that it originally had a wooden roof. The ambulatory and gallery have barrel vaults, except for the center of the south ambulatory at the gallery level. It is possible the ambulatory vaults, which spring from the base of the ambulatory cornices, were originally covered by a timber roof.

​The dome, sanctuary, and vaults of Sts. Sergius and Bacchus were probably decorated with mosaics, perhaps similar to the original non-figurative mosaics of Hagia Sophia. The floors were originally covered with marble slabs, while the walls were covered with marble revetment similar to those found at Hagia Sophia and San Vitale. There are alternating pairs of greenish verd antique and red-veined Synnada marble columns between alternating exedras. The rest of the surviving interior marble decorations are made of gray-veined Proconessian marble. The columns at the ground level are crowned by the so-called “fold” or “melon” capitals, which support an inscribed horizontal entablature of 29 marble blocks at the level of the gallery floor. The gallery columns are crowned by Ionic impost capitals, which support triple arches. These 32 capitals were decorated with the monograms of Justinian and Theodora as well as the imperial title basileos. Its entablature was elaborately carved with an extensive imperial inscription and ornamental motifs, including egg-and-dart, tendril, and dentil decorations. The soffits of the architrave have rosette, square, and diamond designs. The lower cornices on the piers are decorated with split palmettes with pine cones or artichokes. There are egg-and-dart cornices above the gallery level. Masons’ marks can be found on several marble pieces, including reused slabs. Whatever remained of the Byzantine liturgical furniture was removed or reused when it was converted into a mosque. Two Late Antique marble panels, which were perhaps originally used as chancel screens for the templon, were used as the sides of the platform of the minbar. They are very similar in style to marble screens from San Vitale. Spolia can also be seen in the muezzin’s lodge and the Ottoman staircase to the gallery.

It seems that the Church of Sts. Sergius and Bacchus was built between the Palace of Hormisdas and Sts. Peter and Paul. Sts. Sergius and Bacchus apparently communicated with the adjacent basilica and palace through open arcades on both floors. It is generally held that the Church of Sts. Peter and Paul was on its southern side, while the palace was on its northern side. Evidence of these lost buildings can still be seen on the north and south walls of Sts. Sergius and Bacchus. 

The north façade mostly consists of its original brick masonry. There is a walled-up triple arcade on both the ground and gallery levels, which is believed to be an entrance. The cornices of this entrance have also been partially preserved in both the interior and exterior. The side entrances on both floors in the south wall are still intact. These entrances are believed to have provided access to the adjacent Palace of Hormisdas and Sts. Peter and Paul. On the north façade, there are three spur walls jutting out. The first and third spur walls are mainly composed of Justinianic brick; the first spur wall also contains the springing of an arch. The north wall has two large walled-up arches between these spur walls; the masonry is similar to the original construction of Sts. Sergius and Bacchus. The masonry above the walled-up triple arcade has been altered, as if the vaulting or roofing was torn away. The masonry of the northeast corner is also similarly made of irregular stones and presumably belonged to another structure that was lost and had to be repaired.

The south wall is almost two times thicker and 2.5 m shorter than the north wall. Rectangular spaces project south of the ambulatory into this thicker wall. The irregularities of the south wall are arguably evidence of Sts. Peter and Paul built to the south. The double thickness, often considered to include buttresses, is also argued to be an incorporation of this older church’s north wall. However, there are several types of masonry in the south wall, suggesting multiple phases and repairs. It has three large brick arches perhaps from the original construction as well as rectangular window frames and windows with pointed arches that were irregularly added to the façade during the Ottoman era. Other sections of the façade have alternating bands of brick and stone, irregular stones or brick. During the 2003-2006 restoration, excavations were made along the exterior of the south façade, revealing brick foundations. It seems to rest on a foundation of ashlar placed over a filling layer of limestone, clay, sand, and presumably remains of older building structures. It has been argued that the south wall belongs to an earlier phase (namely the Basilica of Sts. Saints Peter and Paul), the additions of buttresses during the Byzantine era, or later Byzantine and perhaps Ottoman repairs.

Even though the church was converted, its original form is substantially intact, with Ottoman additions mostly limited to adding a porch where the atrium was once located, adding new windows, and plastering and painting the interior. It has suffered from at least nine major earthquakes since it was built. The building shows signs of significant repairs and restoration, which took place in both the Byzantine and Ottoman eras. Its close proximity to the railway, built just to the south in the 1860s, also probably damaged the building in the late nineteenth and twentieth centuries. When it was restored in 1955, the exterior plaster was removed except for the dome. It was restored in 2003-2006 after several cracks and deformations in the dome and walls were documented. The building was also excavated during the restoration work. The area along portions of its walls was excavated, which uncovered remains of an additional structure along its southern wall. Excavations under the floor, which rose during the Ottoman era, uncovered a crypt and graves, traces of its marble revetment and pavement, remains of a stylobate, and water drainage channels. The Byzantine column shafts, capi­tals, and bases were also cleaned during the restoration.

The debate about its dating is also linked to proposals about its original function and design. It has generally been argued that it was built either as a palace church or a refuge for non-Chalcedonian (Monophysite) monks. The first proposal considers Sts. Sergius and Bacchus as a type of palace church that follows a tradition of octagonal palatial chapels. Accordingly, it was argued that the construction of the church began before 527, when Justinian was still living at the Palace of Hormisdas before he became emperor. Alternatively, as sources indicate that the Palace of Hormisdas was used to house non-Chalcedonian (Monophysite/Miaphysite) refugees under Theodora’s protection in the early 530s, it has been seen as following an octagonal martyrium. Sts. Sergius and Bacchus also could have been built after the Palace of Hormisdas was incorporated into the Great Palace around 532. Regardless, Sts. Sergius and Bacchus certainly shares features of earlier octagonal churches, such as mid fifth-century rebuilding of the octagonal church at Philippi as well as several centralized churches in Syria. San Vitale, built by Justinian in Ravenna around the same time, is the closest in design, though other lost Justinianic buildings, such as the Church of St. John Prodromos at the Ioukoundianai Palace in the Hebdomon, also had similar plans. Its cruciform crypt in the apse is similar to the fifth-century crypts at Stoudios Monastery and the Chalkoprateia Church. Depending on its date, it could be regarded as Justinian’s architectural experiment, which later influenced the design of the monumental Hagia Sophia. It has even been suggested that the sophisticated design of the interior could be viewed as a remarkable study in geometry or even reflects Neoplatonic thought.