In a colorful ceremony, Bartholomeos I was installed Saturday as the 273rd ecumenical patriarch of the world's 200 million Orthodox Christians.
Bells pealed as Bartholomeos I walked through a throng of faithful into St. George Church.
The 51-year-old primate, elected Oct. 22 after the death of Dimitrios I, sat on a gilded wooden throne as members of the Holy Synod recited prayers and handed him the patriarchal scepter, symbol of his spiritual power and leadership.
Bartholomeos I has pledged to continue seeking common ground with the Vatican and aiding Orthodox churches in Eastern Europe.
Among those attending the ceremony were President Bush's brother, William, Greek Prime Minister Constantine Mitsotakis and Archbishop Iakovos of the Orthodox Church of North and South America.
Bartholomeos I presides over 14 autonomous Orthodox churches, including those of Greece, Albania, Bulgaria, Serbia, Romania and Russia.
Turkey considers the patriarchate a Turkish institution.