Haggia Sophia (now a mosque) became a center of Orthodox Christianity

Political differences between the eastern and western portions of the Roman empire, different theological traditions, and various matters of worship and pastoral practice contributed to a formal breach between East and West that occurred in 1054. In that year eastern leaders suppressed Latin customs in the East and Latin leaders suppressed Greek customs in the West. Pope Leo IX exacerbated the conflict by declining to use the title "Ecumenical Patriarch" for the patriarch of Constantinople and by insisting on use of the filioque clause in the Nicene Creed. Patriarch and pope then exchanged excommunications. Negotiations to heal the schism continued through the fifteenth century, but failed. East and West remain separated to the present, but in 1965 Pope Paul VI and Patriarch Athenagoras nullified the condemnations or anathemas of 1054.