Proper noun
Phlegethon
(Greek mythology) A river of fire in Hades.
Synonym: Pyriphlegethon
He leads the centaurs in Hell 's Circle of Violence where they fire their arrows at any of the damned that try to escape from the Phlegethon. Source: Internet
Virgil describes it in the Aeneid as a gigantic place, surrounded by the flaming river Phlegethon and triple walls to prevent sinners from escaping from it. Source: Internet