The single fact (so often insisted upon), that all Greeks were admissible, is sufficient alone to prove that no secrets incompatible with the common faith, or very important in themselves, could either have been propounded by the priests or received by the audience.

And it may be further observed, in corroboration of so self-evident a truth, that it was held an impiety to the popular faith to reject the initiation of the mysteries--and that some of the very writers, most superstitious with respect to the one, attach the most solemnity to the ceremonies of the other.
XVI.

Sanchoniathon wrote a work, now lost, on the worship of the serpent.

This most ancient superstition, found invariably in Egypt and the East, is also to be traced through many of the legends and many of the ceremonies of the Greeks.

The serpent was a frequent emblem of various gods--it was often kept about the temples--it was introduced in the mysteries--it was everywhere considered sacred.
Singular enough, by the way, that while with us the symbol of the evil spirit, the serpent was generally in the East considered a benefactor.
In India, the serpent with a thousand heads; in Egypt, the serpent crowned with the lotos-leaf, is a benign and paternal deity.