Phlegethon

In Greek mythology, the river Phlegethon (Ancient Greek: Φλεγέθων, lit. 'flaming') or Pyriphlegethon (Πυριφλεγέθων, 'fire-flaming') was one of the five rivers in the infernal regions of the underworld, along with the rivers Styx, Lethe, Cocytus, and Acheron.