“The tests put upon candidates for the [Druidical] priesthood are immensely severe.  For example, there is a test of poetical composition.  The candidate must lie naked all night in a coffin-like box, only his nostrils protruding above the icy water with which it is filled, and with heavy stones laid on his chest.  In this position he must compose a poem of considerable length in the most difficult of the many difficult bardic metres, on a subject which is given him as he is placed in the box.  On his emergence next morning he must be able to chant this poem to a melody which he has been simultaneously composing, and accompany himself on the harp.  Another test is to stand before the whole body of Druids and be asked verse-questions in riddling form which must be answered in further riddles, also in verse.  These riddles all refer to obscure incidents in the sacred poems with which the candidate is supposed to be familiar.  Besides all this he must be able to raise magic mists and winds and perform all sorts of conjuring tricks.”

--  Robert Graves, Claudius the God