24 It is a source of joy to see that the many ecumenical meetings almost always include and indeed culminate in prayer. The Week of Prayer for Christian Unity , celebrated in January or, in some countries, around Pentecost, has become a widespread and well established tradition. But there are also many other occasions during the year when Christians are led to pray together. In this context, I wish to mention the special experience of the Pope's pilgrimages to the various Churches in the different continents and countries of the present-day oikoumene . I am very conscious that it was the Second Vatican Council which led the Pope to exercise his apostolic ministry in this particular way. Even more can be said. The Council made these visits of the Pope a specific responsibility in carrying out the role of the Bishop of Rome at the service of communion. My visits have almost always included an ecumenical meeting and common prayer with our brothers and sisters who seek unity in Christ and in his Church . With profound emotion I remember praying together with the Primate of the Anglican Communion at Canterbury Cathedral (29 May 1982); in that magnificent edifice, I saw "an eloquent witness both to our long years of common inheritance and to the sad years of division that followed ". Nor can I forget the meetings held in the Scandinavian and Nordic Countries (1-10 June 1989), in North and South America and in Africa, and at the headquarters of the World Council of Churches (12 June 1984), the organization committed to calling its member Churches and Ecclesial Communities "to the goal of visible unity in one faith and in one Eucharistic fellowship expressed in worship and in common life in Christ". And how could I ever forget taking part in the Eucharistic Liturgy in the Church of Saint George at the Ecumenical Patriarchate (30 November 1979), and the service held in Saint Peter's Basilica during the visit to Rome of my Venerable Brother, Patriarch Dimitrios I (6 December 1987)? On that occasion, at the Altar of the Confession, we recited together the Nicene-Constantinopolitan Creed according to its original Greek text. It is hard to describe in a few words the unique nature of each of these occasions of prayer. Given the differing ways in which each of these meetings was conditioned by past events, each had its own special eloquence. They have all become part of the Church's memory as she is guided by the Paraclete to seek the full unity of all believers in Christ.
Source: Ut Unum Sint (Vatican.va)