6. When Demetrius died in 231, Heraclas, who for some years had been
associated with Origen at the 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 {peri Physeôs}, 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.