Marcus I ( el, Μᾶρκος Αʹ; died 211) was the

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 ...

for 13 years (198–211 AD). He succeeded Bishop Olympianus. His term of office took place during the persecution of Christians by Emperor

Septimius Severus Lucius Septimius Severus (; 11 April 145 – 4 February 211) was Roman emperor from 193 to 211. He was born in Leptis Magna (present-day Al-Khums, Libya) in the Roman province of Africa. As a young man he advanced through the customary suc ...

. His successor was

Philadelphus ''Philadelphus'' () (mock-orange) is a genus of about 60 species of shrubs from 3–20 ft (1–6 m) tall, native to North America, Central America, Asia and (locally) in southeast Europe. They are named "mock-orange" in reference to their ...

Sources

Marcus I page on Ecumenical Patriarchate website
2nd-century Romans 3rd-century Romans 2nd-century Byzantine bishops 3rd-century Byzantine bishops Roman-era Byzantines Bishops of Byzantium 211 deaths Year of birth unknown {{EarlyChurch-bishop-stub