The more systematic instruction of those who had been already admitted to the order of Catechumens was entrusted to persons appointed to this special duty.  Thus Origen “was in his eighteenth year when he took charge of the Catechetical School at Alexandria,” which “was entrusted to him alone by Demetrius, who presided over the Church Euseb. H. E. vi. 3.:”  and S. Augustine’s Treatise, De Catechizandis Rudibus, was addressed to Deogratias, who being a Deacon at Carthage, and highly esteemed for his skill and success as a Catechist, felt so strongly the importance of the work and his own insufficiency, that he wrote to Augustine for advice as to the best method of instructing those who were brought to him to be taught the first elements of the Christian Faith.