Sabbatios was the oldest son of the Roman Emperor Leo V the Armenian (813–820). After Leo deposed Michael I and ascended the throne on Christmas 813, he had the young Sabbatios crowned co-emperor and renamed Constantine. This name was not chosen by chance, as both were iconoclasts who reinstated the iconoclasm of Emperor Leo III the Isaurian (717–741) and his son Constantine V (741–775). In 815 on Easter, Constantine nominally presided, as his father's representative, over a Church Synod in Constantinople, which reinstated the ban on the veneration of icons.
After the assassination of his father on Christmas 820 by Emperor Michael II the Amorian (820–829), Constantine was banished to the island of Prote along with his mother Theodosia and three brothers Basil, Gregory and Theodosios. There, the four brothers were castrated and tonsured as monks. This was done to prevent them from ever usurping the throne of the Roman Empire, since the emperor was required to be healthy and strong in order to be considered valid for the position, and the empire relied on them for producing successors to their dynasty.
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| Emperor Leo V and his co-emperor and son Constantine |
John Zonaras goes on to record the following significant incident in his Extracts of History. After the four sons of Leo were castrated, Theodosios died and young Constantine lost his voice. This caused Constantine, who had previously promoted iconoclasm, to forsake the error of his past and that of his father, and to fervently entreat God and St. Gregory the Theologian, whose icon he wept and prayed before, asking him to restore to him his voice. That night he saw the great Gregory in a vision, saying to him, "I have heard your prayers, and given to you what you asked for." He then got up and was given by this great Father a book to read aloud, and he read, "Again my Jesus, and again a mystery...." By reading St. Gregory's 39th Oration on Theophany, it was demonstrated to him that he regained his voice for renouncing his past error. Thus the youth glorified God and the Saint.
Constantine and his brothers spent the rest of their days on the island of Prote as monks, although Emperor Michael allowed them to keep part of the proceeds from their confiscated estates for their and their servants' upkeep.