Zeyrek Mosque is the largest Byzantine church still standing in Istanbul after Hagia Sophia — and it is really three churches built shoulder to shoulder. Empress Eirene raised the first in the twelfth century for the Monastery of Christ Pantokrator; after her early death, John II Komnenos added a second and joined the pair with a domed chapel, a mausoleum where emperors of two dynasties were laid to rest. The monastery also ran a hospital renowned far beyond the city. After 1453 the complex passed to a scholar named Molla Zeyrek, whose lessons gave the mosque and the hill around it their name.
Inside, the space feels tall and bare, its brick arches stripped back to bone. Underfoot lies the reason many come: a floor of interlocking coloured marble — swirling discs and knotted borders — among the finest to survive from Byzantium, long hidden beneath timber boards. Fragments of coloured glass, rare from this age, were recovered here too. A long restoration has left the interior quiet and luminous. Outside, the mosque stands amid steep lanes of leaning wooden houses, the Golden Horn glinting below — one of the oldest streetscapes left in the city.