Phlegethon

In Greek mythology, the river Phlegethon ("lake of fire") was one of the five rivers of the underworld, along with the rivers Styx, Lethe, Cocytus, and Acheron. It flowed with fire that burned but did not consume fuel. 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 him to Hades. Eventually when Zeus accepted her river to flow through, they reunited.In Dante's Inferno Phlegethon is described as a river of blood that boils souls. It is in the Seventh Circle and is guarded by centaurs. Here are punished the shades who committed crimes of violence against their fellow men (see Canto XI, 34-39). Here are murderers and tyrants; men who through their violent deeds in life caused hot blood to flow and now themselves sunk in flowing, boiling blood.
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[Greek] The river that flows with fire which burns and does not consume. It is one of the five principal rivers in the realms of Hades.