civil importance of a city as a determining factor in its ecclesiastical position; but he strongly supported its dogmatic decrees, especially when, after the accession of Leo I (457), there seemed to be a disposition toward compromise with the Eutychians. Teaching on Christ Leo's writings (both the sermons and the letters) are mostly concerned with theological questions concerning the person of Jesus Christ (Christology) and his role as mediator and savior (Soteriology), which is partially connected to the Council of Chalcedon in which Roman legates participated in Leo's name. Subsequently, through numerous letters addressed to bishops and members of the imperial family, Leo incessantly worked for the propagation and universal reception of the faith in Christ as defined by Chalcedon, also in the eastern part of the Roman empire. Leo defends the true divinity and the true humanity of the one Christ against heretical one-sidedness. He takes up this topic also in many of his sermons, and over the years, he further develops his own original concepts. A central idea around which Leo deepens and explains his theology is Christ's presence in the Church, more specifically in the teaching and preaching of the faith (Scripture, Tradition and their interpretation), in the liturgy (sacraments and celebrations), in the life of the individual believer and of the organized Church, especially in a council. To Leo the Great, Mariology is determined by Christology. If Christ were divine only, everything about him would be divine. Only his divinity would have been crucified, buried and resurrected. Mary would only be the mother of God, and Christians would have no hope for their own resurrection. The nucleus of Christianity would be destroyed. The most unusual beginning of a truly human life through her was to give birth to Jesus, the Lord and Son of King David. Heir of Peter Leo assumed the papacy at a time of increasing barbarian invasions; this, coupled with the decreasing imperial authority in the West, forced the Bishop of Rome to take a more active part in civil and political affairs. He was one of the first bishops of Rome to promote papal primacy based on succession from Peter the Apostle; and he did so as a means of maintaining unity among the churches. Besides recourse to biblical language, Leo also described his own special relationship with Peter in terms derived from Roman law. He called himself the (unworthy) heir and