Complete Works XVIII: Against Celsus I-IV (Lommatzsch)

Origen, however, who wrote against that sacred head, Celsus the Stoic, having accurately searched all the sects, was a most learned philosopher.

Although Origen sometimes easily believes that Celsus, the author of the Alethes Logos True Discourse, is the same person who published many writings against magic, and who also composed two other books "in a true discourse" against the Christian religion, and was most addicted to the Epicurean sect, yet sometimes he fears to assert that it is one and the same person, because the author of the Alethes Logos sometimes appears to follow Plato and to admit magic. See book I against Celsus, no. 68, and book IV, no. 36. Nevertheless, in book I, no. 8, he thinks that Celsus, not unaware that he could not confess himself an Epicurean without detracting from the faith of what he was about to say, therefore conceals the dogmas which are of Epicurus, and pretends to follow Plato at times, so that the calumnies which he prepares against the Christians might seem more plausible. Be that as it may, Celsus, whom Origen refutes, could not have written his Alethes Logos before the reign of Marcus Aurelius, since, as Origen testifies in book V, no. 62, he not only mentioned in that work the Marcionites, who only arose around the year of Christ 142, but also the Marcellians, who took their name from a certain woman, Marcellina, of the sect of the Carpocratians, who, as Irenaeus testifies in book I, chapter 24, came to Rome under Anicetus after the year of Christ 157. It is very likely, however, that he composed this work during the burning persecution of Marcus Aurelius against the Christians, if indeed, as Origen testifies in book VIII, no. 69, he asserts that the Christians hide everywhere to avoid the danger of death, for which they were sought. This is without a doubt the Celsus of whom Chrysostom says these things in his 6th Homily on the Epistle to the Corinthians: "Those who have spoken against us are sufficient to testify to the antiquity of the books."

So far, Spencer.