The seat of the Ecumenical Patriarchate of Constantinople at Fener (Phanar; map) has been here on the Golden Horn since 1601, a century and a half after Constantinople was conquered from the Byzantines in 1453 and became Istanbul.
His All-Holiness Bartholomew I, elected in 1990 to be the 270th Archbishop of Constantinople - New Rome and Ecumenical Patriarch, claims primacy over the 300 million Orthdox Christians of churches in North America, the United Kingdom, Australia and most of Europe.
Today you can visit the patriarchate and its glittering, historic patriarchal Church of St George on most days of the year. Admission is free.
If you walk from Ayvansaray, be sure to have a look at the wonderful Church of St Stephen of the Bulgars, the gun-metal grey church right on the shore of the Golden Horn. Maanufactured in Vienna, its hundreds of cast-ironparts were floated down the Danube on barges, and the church was bolted together in Constantinople.