AVERNUS LACUS or AVERNI LACUS(Ἄορνος λίμνη: Lago d'Averno), a small lake in Campania, between Cumae and the Gulf of Baiae. It occupies the crater of an extinct volcano, the steep sides of which rising precipitously around it, and covered in ancient times with dark and shaggy woods, gave it a strikingly gloomy character; and it was probably this circumstance, associated with the sulphureous and mephitic exhalations so common in the neighbourhood, that led the Greeks to fix upon it as the entrance to the infernal regions, and the scene of Ulysses' visit to the shades. How early this mythical legend became attached to the lake we know not, but probably soon after the settlement of the Greeks at Cumae. Ephorus, however, is the earliest writer whom we find cited as adopting it. ( ap. Strab. 5. p. 244.) It was commonly reported that the pestiferous vapours arising from the lake were so strong that no living thing could approach its banks, and even birds were suffocated by them as they flew across it. Hence its Greek name Ἄορνοςwas commonly supposed to be derived from ἀν-and ὄρνις.This is probably a mere etymological fancy: but it is not improbable that there was some foundation for the fact, though it is treated as merely fabulous by Strabo and other writers. Similar effects from mephitic exhalations are still observed in the valley of Amsanctus and other localities, and it must be observed that Virgil, who describes the phenomenon in some detail, represents the noxious vapours as issuing from a cavern or fissure in the rocks adjoining the lake, not from the lake itself; and constantly uses the expression Averna locaor Averna,as does Lucretius also, in speaking of the same locality. But while the lake itself was closely surrounded with dense woods, these would so much prevent the circulation of the air, that the whole of the atmosphere might be rendered pestilential, though in a less degree. In the time of Strabo the woods had been cut down; but the volcanic exhalations seem to have already ceased altogether. (Strab. v. pp. 244, 245; Pseud. Aristot. de Mirab. 102; Antig. Caryst. 167; Diod. 4.22; Verg. A. 3.442, 6.201, 237—242 ; Lucr. 6.739—749; Sil. Ital.; Nonius, 1. p. 14; Daubeny on Volcanoes, p. 199.)
The lake itself was of nearly circular form, about a mile and a half in circumference, though Diodorus reckons it only 5 stadia; and like most volcanic lakes, of great depth, so that it was believed to be unfathomable. (Lycophron. Alex. 704; Diod. l. c.;Pseud. Arist. l. c.;Lucan (Luc. 2.665.) It seems to have had no natural outlet; but Agrippa opened a communication between its waters and those of the Lucrine Lake, so as to render the Lake Avernus itself accessible to ships; and though this work did not continue long in a complete state, there appears to have always remained some outlet from the inner lake to the Gulf of Baiae. (Strab. l. c.;Cassiod. Var. 9.6. For further particulars concerning the work of Agrippa see LUCRINUS LACUS) At a subsequent period Nero conceived the extravagant project of constructing a canal, navigable for ships from the Tiber to the Lake Avernus, and from thence into the Gulf of Baiae; and it appears that the works were actually commenced in the neighbourhood of the Avernus. (Suet. Nero 31; Plin. Nat. 14.6. s. 8; Tac. Ann. 15.42.) There existed from very early times an oracle or sanctuary on the banks of the lake, connected with the sources of mephitic vapours; and this was asserted by many writers to be the spot where Ulysses held conference with the shades of the departed. It was pretended that the Cimmerians of Homer were no others than the ancient inhabitants of the banks of the lake, and his assertion that they never saw the light of the sun, was explained as referring to their dwelling in subterranean abodes and caverns hollowed in the rocks. (Ephorus ap. Strab. l. c.;Lycophr. 695; Max. Tyr. Diss. 14.2; Sil. Ital..) The softness of the volcanic tufo of which the surrounding hills are composed, rendered them well adapted for this purpose; and after the whole neighbourhood had been occupied by the Romans, Cocceius carried the road from the lake to Cumae, through a long grotto or tunnel. (Strab. 5. p. 245.) A similar excavation, still extant on the S. side of the lake, is now commonly known as the Grotta della Sibilla;it has no outlet, and was probably never finished. Those writers who placed here the Cimmerians of Homer, represented them as having been subsequently destroyed (Ephorus, l. c.;Plin. Nat. 3.5. s. 9); but the oracle continued down to a much later period; and the lake itself was regarded as sacred to Proserpine or Hecate, to whom sacrifices were frequently offered on the spot. It was under pretence of celebrating these sacred rites that Hannibal in B.C. 214 visited the Lake Avernus at the head of his army; but his real object, according to Livy, was to make an attempt upon the neighbouring town of Puteoli. (Liv. 24.12, 13; Sil. Ital.—160.)
There exist on the SE. side of the lake the picturesque ruins of a large octagonal vaulted edifice, built of brick, in the style of the best Roman works; this has been called by some writers the temple of Proserpine; but it is more probable that it was employed for thermal purposes.
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