Philadelphus (? – 217) is referred to as the first
bishop of Byzantium
The ecumenical patriarch ( el, Οἰκουμενικός Πατριάρχης, translit=Oikoumenikós Patriárchēs) is the archbishop of Constantinople (Istanbul), New Rome and ''primus inter pares'' (first among equals) among the heads of the ...
after the eight-year administration of the Church of Byzantium by a priest whose name has not been recorded. He was bishop for six years (211–217).
Sources
Οικουμενικό Πατριαρχείο
3rd-century people from Byzantium
Bishops of Byzantium
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