Church of SS Sergius and Bacchus: one of the Christian churches in ancient Constantinople.
The church of SS. Sergius and Bacchus in Constantinople is dedicated to two Roman soldiers who were tortured to death in 303. According to a legend, Bacchus was flogged to death first, while Sergius survived and was brought to the fort at Resafa, not far from the Euphrates, where he was again tortured. Here, the spirit of Bacchus appeared to him, and encouraged him to remain steadfast in his Christian beliefs. Sergius was in the end beheaded. The two soldiers were recognized as the patron saints of all soldiers in the Roman and Byzantine armed forces.
Their cult was immensely popular in Syria, and soon spread to other parts of the Roman empire. The emperor Justinian (r.527-565) was one of the most ardent devotees. As a youth, he had been condemned to death because he was believed to have plotted against the emperor Anastasius I (r.491-518), but the twin saints had, according to a legend, in a dream appeared to the ruler, who had now understood that Justinian was innocent - or that God had greater plans with the man - and had released him.
It comes as no surprise that Justinian dedicated a church to SS. Sergius and Bacchus. The grounds on which he built the sanctuary were not far from the Hormisdas Palace, where the emperor used to live - a bit to the west, to be precise, close to the Sea Walls. Construction started as soon as Justinian ascended to the throne in 527. The architect was Anthemius of Tralles, who was better known as a mathematician and the author of a book on burning mirrors, the Paradoxographia, (which was to become notorious because it is the origin of the fairy tale that Archimedes had constructed burning mirrors during the siege of Syracuse).
The church of SS. Sergius and Bacchus was a complex project, because a second church, which was designed as a basilica (with three straight naves) was very close to it, and in fact shared the entrance (narthex) with the new church. It is not recorded to whom this second church was dedicated, and no traces of it are left. Construction of the SS. Sergius and Bacchus took several years, but the project was finished before 536.
The significance of this monument is that its octogonal design was later, on a much larger scale, reused by Anthemius when he (together with Isidore of Miletus) built the Church of the Divine Wisdom, the Hagia Sophia. An old description of the SS. Sergius and Bacchus is offered by Justinian's contempory Procopius:
Justinian built a shrine to the famous Saints Sergius and Bacchus, and then also another shrine which stood at an angle to this one. These two churches do not face each other, but stand at an angle to one another, being at the same time joined to each other and rivalling each other; and they share the same entrances and are like each other in all respects, even to the open spaces by which they are surrounded; and each of them is found to be neither superior nor inferior to the other either in beauty or in size or in any other respect. Indeed each equally outshines the sun by the gleam of its stones, and each is equally adorned throughout with an abundance of gold and teems with offerings. In just one respect, however, they do differ. For the long axis of one of them is built straight, while in the other church the columns stand for the most part in a semi-circle. But whereas they possess a single colonnaded stoa, called a narthex because of its great length, for each one of their porches, they have their propylaea entirely in common, and they share a single court, and the same doors leading in from the court, and they are alike in that they belong to the Palace.note[Procopius, Buildings 1.4.3-7.]
The dome is very remarkable, because it consists of eight flat and eight concave sections, which rest on eight piers. This is unique, but it might well have become extremely popular. Many churches in this age were very innovative and experimental; the architects were still looking for new forms. Eventually, the dome of the Hagia Sophia was to receive a different design, which became the new standard.
The church was converted into a mosque in the first years of the sixteenth century and is now known as the Küçük Ayasofya, the "Little Hagia Sophia".