The Circle of Fire was created by Hera. It had the power to kill immortality. When Hera stole the Eternal Torch from Prometheus she hid it within the Circle of Fire to make sure no one could get it back. Hercules knew the cost and still chose to enter the Circle to retrieve the torch. Zeus interceded on his behalf and Hera backed down, allowing the torch to be given back to Prometheus. Later, Hercules took fire from the circle to create a second one which he used to cure his friend Cheiron's wound and make him mortal.