The River Styx is a prominent place in Greek mythology, known as the river that separated the world of the living from the underworld. It was said to be a dark and gloomy river, guarded by the ferryman, Charon, who would transport the souls of the dead across the river to the underworld.

The River Styx was also known for its power to confer invulnerability. In Greek mythology, it was said that those who were dipped in the River Styx would become invulnerable, except for the spot where they were held, as it was believed that the water of the river had magical powers. This is why Thetis dipped Achilles in the river, however, she held him by the heel, which remained unprotected and would be his weak spot.

The River Styx was also known for being the location where oaths were taken, and it was believed that those who swore an oath on the River Styx would be bound by it. This is why in many myths, gods and heroes take oaths on the River Styx in order to make them more binding.