Io is known from the Greek tragedy Prometheus Bound. She is a girl who is partly a cow and she is portrayed as a total victim. Prometheus tells her fortune which involves great wanderings from the Black Sea down to Egypt where she gives birth to a boy who will grow up to be the first king of Egypt. I find it fascinating he’s not the first pharoah but the first king which suggests his time was before the First Kingdom. The Greek myths hopelessly muddy the story but that seems to be the essential fact. Then I was reading up on the founding of Byzantium (the city that became Constantinople and is now Istanbul.) It was a Greek colony founded around 800 BCE. But then I read some other myths about its founding. That Io stopped there and gave birth to a daughter and then resumed her wanderings down to Egypt. Daughter grew up withe horns of a cow so no one liked her until she met Poseidon. Their son was Byzas who then founded the city Byzantium. So myth is making a very clear connection between the ancient Black Sea and ancient Egypt. This to me is very suggestive of either very ancient trade routes or a mass migration or ????