Aver'nus, a lake now called Lago d'Averno, in Campania, Italy, between the ancient Cumae and Puteoli, about eight miles from Naples. It occupies the crater of an old volcano, and is in some places 180 feet deep. Formerly the gloom of its forest surroundings and its sulphurous vapors caused it to be regarded as the entrance to the infernal regions. It was the fabled abode of the Cimmerians, and was especially dedicated to Proserpine.