The building we know today as the Little Hagia Sophia Mosque is one of the most important Early Byzantine structures to have survived in Istanbul. It was built in the first half of the sixth century, during the reign of Emperor Justinian I, as a church dedicated to Saints Sergius and Bacchus. Created shortly before the same emperor commissioned Hagia Sophia, it is an important example of the new spatial and structural experiments with domes that marked Justinianic architecture.

An old story about the foundation of the church reaches back to the years before Justinian became emperor. According to the legend, he was accused of taking part in a conspiracy against his uncle, Emperor Justin I. Saints Sergius and Bacchus appeared to the emperor in a dream and testified to Justinian’s innocence, saving him from punishment. After becoming emperor, Justinian is said to have built the church in gratitude to the two saints. History and legend merge in this account, which became part of the religious identity of the building over the centuries.

From the outside the building appears relatively restrained, but its most impressive qualities emerge inside. An octagonal central space is set within an irregular quadrilateral and covered by a dome divided into sixteen sections, alternating between flat and concave surfaces. This creates an undulating sense of movement toward the dome. Two-storey galleries and semicircular exedrae surround the centre, producing spaces that flow into one another rather than being separated by rigid boundaries. Related experiments with centralized planning can be seen in sixth-century buildings such as San Vitale in Ravenna.

For me, some of the most striking interior elements are the columns and their finely carved stonework. Marble columns in green and reddish tones, together with richly carved capitals, surround the lower and upper galleries. Monograms of Justinian and his wife Theodora can still be seen on some capitals. At gallery level, a long Greek inscription runs around the interior. Its twelve hexameter verses praise Justinian, Theodora and Saint Sergius, bringing architecture, ornament, imperial authority and religious devotion together in the same space.

In the early sixteenth century, during the reign of Bayezid II, the church was converted into a mosque by Hüseyin Ağa, the chief of the palace gatekeepers. A mihrab, minbar and minaret were added, while a small Ottoman complex developed around it with a lodge-madrasa, tomb, primary school and bath. Earthquakes, repairs and especially the railway constructed very close to the building in the nineteenth century affected the monument. Despite these changes, the principal Byzantine spatial arrangement and the elements added during the Ottoman period continue to coexist.

When I photographed the building in December 2016, what interested me was not a monument belonging to a single historical period. The columns, capitals, galleries and dome preserve the presence of sixth-century Constantinople, while the mihrab, minbar, courtyard and surrounding structures speak of later Istanbul. For me, this is the particular value of Little Hagia Sophia: it has reached the present not by erasing one period in favour of another, but by carrying the traces of different centuries within the same place.