If you visit the Sokullu Mehmet Paşa mosque featured in the previous article, carry on down the hill after you leave the mosque and you will easily find Küçük Aya Sofya.

It got this name because it is supposed to resemble the real Aya Sofya, in a smaller version, but it was originally the Byzantine church of St Sergius and St Bacchus.

As such it is one of the oldest and most beautiful historic buildings in the city whose construction began under the Emperor Justinian in 527AD.

SS Sergius and Bacchus were the patron saints of Christians within the Roman army, centurions who had been martyred for their faith.

This was the first of many churches that Justinian would build, within Constantinople, and throughout the Byzantine Empire.

It served as a church for nearly a thousand years; then in the first decade of the sixteenth century it was converted into a mosque by Hüseyin Ağa, Chief Black Eunuch during the reign of Beyazit II. Hüseyin Ağa is buried in a tomb in the grounds.

The interior, on a quick glance, looks just like most mosques. But then you notice that the mihrab, placed in the area behind where the altar was sited, is off-centre – a mihrab always has to point directly to Mecca whereas altars just need to aim for the east in general.

Next you can’t help but see the huge marble columns set in pairs supporting the gallery, and from the gallery the dome.

Finally, above the ground floor columns, a carved marble frieze runs all around the building and you don’t have to be fluent in Greek to pick out the names of Justinian and his wife Theodora.

Apparently the walls were originally covered with mosaics and frescoes as richly executed as their counterparts in the main Aya Sofya up the road.

When this writer visited the mosque in December 2010 they had just completed painting the interior, and it is clear the long-hidden decorative works are highly unlikely ever to be revealed again.