Church of St John of Studius ( İmrahor Camii ), Istanbul.

In 463, a monastery, of which this is the church, was established by a Roman named Studius, a consul during the reign of the Emperor Marcian. The monastery, the Studion, was once the most powerful in the Byzantine Empire. The church was converted into a mosque towards the end of the 15th century by İlyas Bey, İmrahor ( Master of the Horse ) to Sultan Beyazıt II. The remains of the monastery were finally destroyed by an eathquake in 1894, which also severely damaged the church/mosque and led to its abandonment.
This view of the apsidal east end of what is the city's oldest surviving church is from İmam Aşir Sokağı, not far from İmrahor İlyasbey Caddesi.