He becomes Head of the Catechetical School

6. When Demetrius died in 231, Heraclas, who for some years had been associated with Origen at the 12 Catechetical School and had just been left in charge of it by him on his final retirement that year from Alexandria, was elected Bishop, while Dionysius, who had himself been a pupil of Origen there, was appointed to fill the vacancy he created. It is possible that the treatise περὶ Φύσεως, extracts from which are given below (on pp. 91 ff.), was composed while Dionysius held this important post, and that a commentary on Ecclesiastes, some genuine fragments of which probably remain, belongs to the same period. The former of these is much the more valuable work, for in it for the first time a Christian undertook systematically to refute the atomistic theories of Epicurus and his followers.