52 With regard to the Church of Rome and the Ecumenical Patriarchate of Constantinople, the process which we have just mentioned began thanks to the mutual openness demonstrated by Popes John XXIII and Paul VI on the one hand, and by the Ecumenical Patriarch Athenagoras I and his successors on the other. The resulting change found its historical expression in the ecclesial act whereby "there was removed from memory and from the midst of the Church" the remembrance of the excommunications which nine hundred years before, in 1054, had become the symbol of the schism between Rome and Constantinople. That ecclesial event, so filled with ecumenical commitment, took place during the last days of the Council, on 7 December 1965. The Council thus ended with a solemn act which was at once a healing of historical memories, a mutual forgiveness, and a firm commitment to strive for communion. This gesture had been preceded by the meeting of Pope Paul VI and Patriarch Athenagoras I in Jerusalem, in January 1964, during the Pope's pilgrimage to the Holy Land. At that time Pope Paul was also able to meet Benedictos, the Orthodox Patriarch of Jerusalem. Later, Pope Paul visited Patriarch Athenagoras at the Phanar (Istanbul), on 25 July 1967, and in October of the same year the Patriarch was solemnly received in Rome. These prayer-filled meetings mapped out the path of rapprochement between the Church of the East and the Church of the West, and of the re-establishment of the unity they shared in the first millennium. Following the death of Pope Paul VI and the brief pontificate of Pope John I, when the ministry of Bishop of Rome was entrusted to me, I considered it one of the first duties of my pontificate to renew personal contact with the Ecumenical Patriarch Dimitrios I, who had meanwhile succeeded Patriarch Athenagoras in the See of Constantinople. During my visit to the Phanar on 29 November 1979, the Patriarch and I were able to decide to begin theological dialogue between the Catholic Church and all the Orthodox Churches in canonical communion with the See of Constantinople. In this regard it would seem important to add that at that time preparations were already under way for the convocation of a future Council of the Orthodox Churches. The quest for harmony between them contributes to the life and vitality of these sister Churches; this is also significant in view of the role they are called to play in the path towards unity. The Ecumenical Patriarch decided to repay my visit, and in December 1987 I had the joy of welcoming him to Rome with deep affection and with the solemnity due to him. It is in this context of ecclesial fraternity that we should mention the practice, which has now been in place for a number of years, of welcoming a delegation from the Ecumenical Patriarchate to Rome for the Feast of the Holy Apostles Peter and Paul, as well as the custom of sending a delegation of the Holy See to the Phanar for the solemn celebration of Saint Andrew.
Source: Ut Unum Sint (Vatican.va)