Before we begin our reply, we have to remark that the endeavour to show, with regard to almost any history, however true, that it actually occurred, and to produce an intelligent conception regarding it, is one of the most difficult undertakings that can be attempted, and is in some instances an impossibility. For suppose that some one were to assert that there never had been any Trojan war, chiefly on account of the impossible narrative interwoven therewith, about a certain Achilles being the son of a sea-goddess Thetis and of a man Peleus, or Sarpedon being the son of Zeus, or Ascalaphus and Ialmenus the sons of Ares, or Æneas that of Aphrodite, how should we prove that such was the case, especially under the weight of the fiction attached, I know not how, to the universally prevalent opinion that there was really a war in Ilium between Greeks and Trojans?
And suppose, also, that some one disbelieved the story of Œdipus and Jocasta, and of their two sons Eteocles and Polynices, because the sphinx, a kind of half-virgin, was introduced into the narrative, how should we demonstrate the reality of such a thing? And in like manner also with the history of the Epigoni, although there is no such marvellous event interwoven with it, or with the return of the Heracleidæ, or countless other historical events. But he who deals candidly with histories, and would wish to keep himself also from being imposed upon by them, will exercise his judgment as to what statements he will give his assent to, and what he will accept figuratively, seeking to discover the meaning of the authors of such inventions, and from what statements he will withhold his belief, as having been written for the gratification of certain individuals.
And we have said this by way of anticipation respecting the whole history related in the Gospels concerning Jesus, not as inviting men of acuteness to a simple and unreasoning faith, but wishing to show that there is need of candour in those who are to read, and of much investigation, and, so to speak, of insight into the meaning of the writers, that the object with which each event has been recorded may be discovered.
Source: Against Celsus (New Advent)