In the first part of this study we deal with the relation of Saint Τheodore the Studite to the cities of Thessaloniki and Jerusalem. Having as our main source his massive epistolography, we discuss his views on the place of the patriarch of Jerusalem Thomas and the pope of Rome in the Church. Thomas is the “first” (primus) within the “pentarchy” of the patriarchs, in the so called “five-headed body of the Church” (πεντακόρυφον ἐκκλησιαστικόν σῶμα), where the pope belongs as (...) well. According to Theodore all the patriarchs are “equal”, in the “pentarchy”, the ecclesiological form of the Church’s life of the first millenium. Among them the pope is the first in “order and honour” for being the leader of the “Romaic Church”, “the patriarch of the West”. This title is the traditional one among others, which the pope uses ever since. However, its recent omission from the last edition (2006) of the “Annuario Pontificio”, puts more obstacles to the constant efforts for mutual understanding and sincere and fruitful theological dialogue between the Orthodox and the Roman-Catholic Church. The second part of the study is related to the ecclesiology of “communion” and we make some comments on this central principle of theology. The concept of “communion” should apply to all the ecclesial institutions and it could greatly contribute, in a very positive and constructive way, to the discussions of the problem about the office of “primus” and the way of exercising it in the Catholic Church, with specific reference to the “primacy” of bishop of Rome, in terms of the ecumenical movement and the ecclesial rapprochement. The concept of “communion” may even place the stumbling block of the ecclesial unity, i.e. the “office” of the pope, in the traditional framework, which is the paradigm of the “pentarchy of the patriarchs”. In other words, the way of Church’s life during the first ten centuries. In the last section we briefly discuss the rebeginning of the second phase of the Official Theological Dialogue between the Roman-Catholic and the Orthodox Church (Belgrade 18-25 September 2006), the official visit of pope Benedict 16th to Constantinople (30 November 2006) and the official visit of archbishop of Athens and all Greece Christodoulos to Rome (14 December 2006). These very important events it is hoped that will push forward the essential progress of this dialogue, which some time in the future may lead the two Churches to the full “communion” of faith and sacramental life. (shrink)