According to Herodotus, the Egyptians never sacrifice cows
“for these are sacred to Isis. For the image of Isis is always made in the form of a woman with the horns of an ox, as Io is pictured by the Greeks; and for that reason all Egyptians are alike in treating cows far more holy than other beasts.”
In the above image from Pompeii’s Temple of Isis, we can see that the woman on the left does indeed have have horns, although Isis, on the right, does not. (Just as points of interest, note the diaphanous nature of Isis’ robe, as well as the breast-baring robe of the—I assume—priestess behind Her, who holds a sistrum. The—I again assume—priest beside her holds a sistrum, wand, and situla. We don’t know for certain, but perhaps the artist was depicting the Isiac priestess and priest as he had actually seem them in the temple of Isis. If so, Pompeiian Isiacs were working hard to keep the Egyptian flavor of their rites, even in Italy.)
But back to our subject, which is, who is this Io and why does she receive special consideration from the Goddess Isis?
The story of Io is a Greek myth and apparently a very ancient one. Here’s the tale: Io was a priestess of Hera, even the first priestess of Hera, having established the Goddess’ worship in Argos. Io is also a naiad or water nymph, daughter of the River God, Inakhos. Theoi.com (a truly great mythology website) says that Io, in the Argive dialect, means “the moon.” (Ah ha; very interesting.)
Hera’s ever-unfaithful husband, Zeus, falls in love with the lovely lunar nymph—either because of her great beauty or due to the spells of a iynx (a magical wheel sacred to Hekate; also known as Hekate’s Top). Io had dreams that told her she should indeed surrender to Zeus, but when she told her father about them, he decided a second opinion was in order. After consulting the Delphic oracle and the oracle of Dodona (an oracle of Zeus, by the way), the answer remained the same. So Io went secretly to Zeus and they made love. Now betrayed not only by Her husband but also by Her priestess, Hera was, to say the least, not pleased.
To protect Io, Zeus turned her into a beautiful white cow. Hera, pretending ignorance of the true identity of the lovely cow, promptly demanded that Zeus give the cow to Her. He could do nothing but comply. To guard Her new possession, Hera brought in Argos, Who had a hundred watchful eyes. Due to His many eyes, Argos was able to keep permanent vigil and was therefore a formidable guardian. But Zeus enlisted the aid of Hermes to help Io escape, which He finally did by killing Argos.
Io, still in the form of a cow, made good her escape, so Hera sent a horsefly or gadfly to torment her until she was driven mad. As a mad cow, she wandered and wandered across the world. In her wanderings, she gave her name to many geographic features. For instance, the Ionian Sea is supposed to be named for her. Finally, the white cow, Io, arrives in Egypt.
There she regained her human form—Aeschylus says Zeus healed her—and bore Zeus’ son, Epaphus. Herodotus gives Epaphus as an alternative name for the Egyptian Apis bull; ah ha, again. Other stories have Io, already in human form, kidnapped by Phoenicians or pirates, and brought to Egypt. But Io’s troubles are not yet over, for Hera next ordered the Kouretes (young Divine warriors Who serve the Mother Goddess) to kidnap Epaphus—so once again, Io wandered, this time, searching for her lost son. At last, she learned that the queen of Byblos was raising Epaphus. Io went to Byblos and eventually returned with Epaphus to Egypt where, according to Apollodorus, Io “dedicated an image to Demeter, called Isis by the Aigyptians, as also they called Io herself.”
Although Io’s story seems to be quite old and many ancient texts refer to it, Io’s connection with Isis—or even identification with Isis—is less so. Nevertheless, there are a number of correspondences between Isis and Io. The theme of searching for a loved one, pursued by an enemy is common to both. In fact, both wander twice. Both appear as pure, white cows. Both are associated with the moon. Both are aided by the God of Knowledge; Hermes in the case of Io, Thoth in the case of Isis. In Plutarch’s late version of the Isis-Osiris myth, Isis finds Osiris’ body in Byblos. Io finds her son in Byblos. And in Apuleius’ tale of initiation into Isis’ Mysteries, the theme of being returned to human form after suffering trials in the form of an animal applies to Lucius in Apuleius’ tale and Io in her many myths. A 10th century CE lexicon or encyclopedia, known as the Suidas, makes the identification complete under the entry for Isis:
Isis: She is called Io. She was snatched by Zeus from Argos and he, fearing Hera, changed her first into a white cow, then into a black one, and then into a one that was violet-coloured. After wandering around with her, he came into Egypt. The Egyptians, then, honour Isis, and for this reason they carve the horns of a cow on the head of her statue, alluding to the change from maiden to cow.
It is always interesting to me, and important, I think, that when we first see the connections drawn by the ancients between the Deities (for Io becomes a Goddess), we often find them far-fetched. Yet if we follow the trail a bit more, the associations become much less strained. Io is certainly a case in point. When we look deeper into the myths and stories, we find the holy correspondences. We see the sacred connections. We glimpse a little more of the Divine unity that underlies and interpenetrates all things.