In Greek mythology, the river Phlegethon or Pyriphlegethon was one of the five rivers in the infernal regions of the underworld, along with the rivers Styx, Lethe, Cocytus, and Acheron. Plato describes it as "a stream of fire, which coils round the earth and flows into the depths of Tartarus". It was parallel to the river Styx. It is said that the goddess Styx was in love with Phlegethon, but she was consumed by his flames and sent to Hades. Eventually, when Hades allowed her river to flow through, they reunited.
