Constantinople
A layover in Istanbul gave me a chance to visit two more early Christian churches, built by Justinian in the early 6th century.
Hagia Eirene
Küçük Ayasofya Camii ("Little Ayasofya Mosque") formerly the Church of Saints Sergius and Bacchus
Inside Küçük Ayasofya Camii you can still see the Greek writing on the stone work