Fethiye Mosque holds the third-finest Byzantine mosaics in Istanbul, and it rarely has a queue at the door. It began as the Church of Theotokos Pammakaristos, meaning the All-Blessed Mother of God, built under the Komnenos emperors in the eleventh and twelfth centuries. Its treasure is a small side chapel added around 1310 by Maria, widow of the general Michael Glabas, to shelter his tomb. When Constantinople fell, the church became the seat of the Greek Orthodox Patriarchate for over a hundred years. Late in the 1500s Sultan Murad III converted it into a mosque marking his campaigns in the Caucasus, and named it Fethiye, meaning conquest.
Today the building lives a double life. The old main hall is a working neighbourhood mosque, its Byzantine bays opened out beneath a broad Ottoman-era dome. The side chapel is kept apart as a small museum, and it is the reason you come. You stand in a cramped, luminous space and look up at a stern Christ ringed by twelve prophets, filling the dome. In the apse below, a gold mosaic shows Christ flanked by the Virgin and John the Baptist, an arrangement called a Deesis, close enough to read every face. Outside, the devout old lanes of Çarşamba carry on, unbothered by the marvel behind the wall.