Although Catholics and Orthodox remain estranged on key issues — including married clergy and the centralized power of the Vatican — there have been significant moves toward closer interactions and understanding.
An apostolic letter by John Paul II in 1995 encouraged unity between the two branches of Christianity and opened the way for a historic visit to Rome by Bartholomew I, who is considered the "first among equals" of the Orthodox patriarchs, as well as Catholic-Orthodox conferences.
During the first papal trip to Greece in 2001, John Paul II issued an apology for the ravages of the Fourth Crusade, which in the early 13th century sacked Constantinople, now Istanbul, the seat of the Eastern church. In 2006, Benedict XVI was hosted by the ecumenical patriarchate in Istanbul in a visit that brought protests from some archconservative Orthodox but generally opened room for dialogue on even closer contacts.
Francis was expected to meet with representatives of other religious denominations, including Bartholomew, on Wednesday.
Associated Press writer Brian Murphy in Rome contributed to this report.
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