He played a pipe so enchanting that Argus invited the stranger to share the shade with him. Mercury descended to Earth and wore a shepherd's disguise. Jove felt sorry for Io, and so he sent his son, Mercury, to kill Argus. He took Io to a distant field where he could sit on a mountaintop and guard her. Her father was distraught at the fate of his daughter, and Argus separated the family. During the day when she was allowed to graze she wandered to her father's stream and there she followed him and her sisters, but none recognized her until she scratched her name into the dirt with her hoof. Day and night Argus watched over Io and she was miserable in her new form. Juno gave the heifer to Argus, a man with a hundred eyes, to keep watch over her. Knowing that if he refused to give the heifer to his wife she would become suspicious, Jove agreed. Juno, though suspicious, couldn't help but admire the beautiful animal, and she asked for it as a gift. Jove turned Io into a white heifer so that he wouldn't be caught in his infidelity. Juno, Jove's wife and sister, noticed the fake night that darkened earth and knew that her husband was up to something, so she descended from Olympus and dispersed the clouds. Although he told her who he was, she wouldn't stop running, so he covered the earth in darkness so that she wouldn't be able to run away from him.

When Jove descended to possess her, she ran into the forest. Io, daughter of the river Inachus, caught Jove's eye one day as she was returning from her father's stream.

Ovid metamorphoses book 1