Summary: The present article seeks to present the archdeacon Meliteniotes, an eminent but little known Greek prelate and theologian of the second half of the 13^th century. The sources present him as someone who worked from the very beginning of his activity towards the restoration of communion between Byzantium and the Roman Church. Besides being noble at heart, he was well-versed in the writings of the Greek Fathers, especially those who delve into the trinitarian mystery, including the procession of the Holy Spirit, because that question was groundlessly indicated in Byzantium as the main cause of its breaking away from the Church of Rome. Having arrived at the conclusion that the Greek Fathers had imparted the same teaching on the issue as the Latin Church, and consequently that the declaration of Photius (ek monou tou Patros) did not correspond to the genuine Greek theology, he devoted all his energy and capacity to explain it to his fellow-nationals. Among other things, he laboured hard to prepare the clergy and the people for the Council of Lyons (1274) and to defend the unity that had been restored there. When, however, it was rejected due to the political anxiety of Emperor Andronicus but more so due to the attitude of the people who were themselves instigated by the monks, Constantine Meliteniotes found himself in prison. Despite many proposals attractive from the human point of view, he persevered in in the catholic faith, although in natural perspective there was no hope left for him, since every vestige of union with the Roman Church had been eliminated in Byzantium. His death in prison after 24 years of confinement – together with the death of Patriarch John XI Bekkos, who died in the same place in his fifteenth year of imprisonment, and that of the deacon Gorge Metochites who had to “leave prison” after 40 years of confinement – is an eloquent invitation which he fraternally addresses even today to his fellow-nationals and to other separate Christians of the East, so that they may open their eyes to the possibility and the need for union which results clearly from the teachings of the holy oriental Fathers. To this end, based on what has been affirmed by Saints Basil, Epiphanius, Cyril, the two Gregory’s and others, one should evaluate what the patriarchs Photius and Cerularius, beginning from the 9^th century, have diffused in Byzantium.(The article is written in Latin).