Apollodorus, Library
Sir James George Frazer, Ed.

Argus and Ismene, daughter of Asopus, had a son Iasus, who is said to have been the father of Io.¹ But the annalist Castor and many of the tragedians allege that Io was a daughter of Inachus;² and Hesiod and Acusilaus say that she was a daughter of Piren. Zeus seduced her while she held the priesthood of Hera, but being detected by Hera he by a touch turned Io into a white cow³ and swore that he had not known her; wherefore Hesiod remarks that lover's oaths do not draw down the anger of the gods. But Hera requested the cow from Zeus for herself and set Argus the All-seeing to guard it. Pherecydes says that this Argus was a son of Arestor;⁴ but Asclepiades says that he was a son of Inachus, and Cercops says that he was a son of Argus and Ismene, daughter of Asopus; but Acusilaus says that he was earth-born.⁵ He tethered her to the olive tree which was in the grove of the Mycenaeans. But Zeus ordered Hermes to steal the cow, and as Hermes could not do it secretly because Hierax had blabbed, he killed Argus by the cast of a stone;⁶ whence he was called Argiphontes.⁷ Hera next sent a gadfly to infest the cow,⁸ and the animal came first to what is called after her the Ionian gulf. Then she journeyed through Illyria and having traversed Mount Haemus she crossed what was then called the Thracian Straits but is now called after her the Bosphorus.⁹ And having gone away to Scythia and the Cimmerian land she wandered over great tracts of land and swam wide stretches of sea both in Europe and Asia until at last she came to Egypt, where she recovered her original form and gave birth to a son Epaphus beside the river Nile.¹⁰ Him Hera besought the Curetes to make away with, and make away with him they did. When Zeus learned of it, he slew the Curetes; but Io set out in search of the child. She roamed all over Syria, because there it was revealed to her that the wife of the king of Byblus was nursing her son;¹¹ and having found Epaphus she came to Egypt and was married to Telegonus, who then reigned over the Egyptians. And she set up an image of Demeter, whom the Egyptians called Isis,¹² and Io likewise they called by the name of Isis.¹³