In ancient geography, a volcanic crater lake near Naples, Italy, legendary as the entrance to the underworld in Roman mythology.
From Latin Avernus, from Greek Aornos, meaning 'without birds' (a- meaning without + ornos meaning bird). The name derived from the phenomenon that toxic volcanic gases from the lake killed birds attempting to fly over it.
Avernus was literally called 'the lake where birds die'—and it actually happened due to carbon dioxide seeping from volcanic vents! The Romans then made it the mythological gateway to Hell because the dead zone was already built into reality. Ancient people were great at turning scary nature into religion.
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