The course will examine the patristic period that goes from the Council of Chalcedon (451) to the end of the patristic age traditionally assigned to the East up to John Damascene († 749) and in the West up to Isidore of Seville († 636). Individual authors will be studied and, with particular interest, their theological contributions concerning Christology and developments in the Trinitarian field. We will focus our study, especially on the processes that will lead some movements (monophysitism, adoptionism) to become heterodox and, therefore, the fight against them for the affirmation of the true faith, whose formulation often required considerable effort.