39 Whence, then, do we prove that all these narratives are records of events? From the solemn rites and mysteries of initiation, it is clear, whether those which are celebrated at fixed times and on set days, or those which are taught secretly by the heathen without allowing the observance of their usages to be interrupted. For it is not to be believed that these have no origin, arc practised without reason or meaning, and have no causes connected with their first beginnings.
That pine which is regularly born into the sanctuary of the Great Mother, is it not in imitation of that tree beneath which Attis mutilated and unmanned himself, which also, they relate, the goddess consecrated to relieve her grief? That erecting of phalli and fascina, which Greece worships and celebrates in rites every year, does it not recall the deed by which Liber paid his debt? Of what do those Eleusinian mysteries and secret rites contain a narrative?
Is it not of that wandering in which Ceres, worn out in seeking for her daughter, when she came to the confines of Attica, brought wheat with her, graced with a hind's skin the family of the Nebridae and laughed at that most wonderful sight in Baubo's groins? Or if there is another cause, that is nothing to us, so long as they are all produced by some cause. For it is not credible that these things were set on foot without being preceded by any causes, or the inhabitants of Attica must be considered mad to have received a religious ceremony got up without any reason.
But if this is clear and certain, that is, if the causes and origins of the mysteries are traceable to past events, by no change can they be turned into the figures of allegory; for that which has been done, which has taken place, cannot, in the nature of things, be undone.
Source: Against the Heathen (New Advent)