Among the most characteristic motifs in Greek mythology is the sexual union of a god with a mortal woman and the resultant birth of a hero. The existence of hexameter poetry listing the women thus favoured – the famous women in the underworld in the eleventh book of the Odyssey, and above all the Eoiai – is evidence of an interest in the women involved, not only in their heroic sons, and suggests that already at an early date the theme was the object not merely of passive reception but of an active consciousness. The Eoiai, indeed, saw such unions as an integral part of an earlier and better age, when mortals and immortals were closer:
ξυναὶ γὰρ τότε δαῖτες ἔσαν, ξυνοὶ δὲ θόωκοι
ἀθανάτων τε θεῶν καταθνητοῖς τ' ἀνθρώπων(fr. 1 Μ–W)
But it was not to be supposed that such a potentially rich theme would receive a unitary treatment. Already in their first appearances – at least, the first appearances for us – many individual stories are clearly distinguished by their different circumstances. A common variable is the existence, the kind and the degree of difficulty experienced by the woman as a result of the encounter. Polymele, for instance, mother of Eudorus by Hermes at Iliad
16.179–92, has seemingly no difficulty in leaving her child to be brought up by her father while she goes on to marry a mortal husband. But suffering of some sort is perhaps more usual, and famous sufferers include Cassandra, punished for spurning Apollo's advances; Danae, first imprisoned by her father in a brazen tower to prevent her pregnancy, and then locked in a chest with her baby and set afloat on the waves; and Semele, destroyed when her lover Zeus appeared to her in his true form. Such different experiences could suggest further multiple versions of the same general theme, diverging especially in the consequences of the union (or attempted union) for the mortal partner. Even the same characters could potentially undergo quite different variants of the story; the chief constant is the unfailing popularity of the mythical motif.