Io was, in Greek mythology, a priestess of Hera in Argos, a nymph who was seduced by Zeus, who changed her into a heifer to escape detection. His wife Hera sent ever-watchful Argus Panoptes, with 100 eyes, to guard her, but Hermes was sent to distract the guardian and slay him. Heifer Io was loosed to roam the world, stund by a maddening gadfly sent by Hera, and wandered to Egypt, thus placing her descendant Belus in Egypt; his sons Cadmus and Danaus would then "return" to mainland Greece.
The ancients connected Io with the Moon, and in Aeschylus´Prometheus Bound, where Io encounters Prometheus, she refers to herself as "the horned virgin", both bovine and lunar.
