as with any pagan religion, oral tradition was key.  the romans and greek had laws prohibiting putting it into text, with the excuse that reading would weaken memory and so on.  and there is a case to be made for that certainly, but it has the weakness that when genocidal semites cull all the "brain libraries" you lose most of it.  much survive in folk-lore, myth and what have you, but time coupled with undisciplined passing of knowledge cause great distortion in the information.
Denmark