the one connected with the Lake of Avernus, near Naples.
Cicero[57] describes how, from this lake, "shades, the spirits of the
dead, are summoned in the dense gloom of the mouth of Acheron with salt
blood"; and Strabo quotes the early Greek historian Ephorus as relating
how, even in his day, "the priests that raise the dead from Avernus live
in underground dwellings, communicating with each other by subterranean
passages, through which they led those who wished to consult the oracle
hidden in the bowels of the earth." "Not far from the lake of Avernus,"
says Maximus of Tyre, "was an oracular cave, which took its name from
the calling up of the dead. Those who came to consult the oracle, after
repeating the sacred formula and offering libations and slaying victims,
called upon the spirit of the friend or relation they wished to consult.
Then it appeared, an unsubstantial shade, difficult both to see and to
recognize, yet endowed with a human voice and skilled in prophecy. When
it had answered the questions put to it, it vanished." One is at once
struck with the similarity of this account to those of the
spiritualistic seances of the famous Eusapia in the same part of the
world, not so very long ago. In most cases those consulting the oracle
would probably be satisfied with hearing the voice of the dead man, or
with a vision of him in sleep, so that some knowledge of ventriloquism
or power of hypnotism or suggestion would often be ample stock-in-trade
for those in charge.

This consulting of the dead must have been very common in antiquity.
Both Plato[58] and Euripides[59] mention it; and the belief that the
dead have a knowledge of the future, which seems to be ingrained in
human nature, gave these oracles great power. Thus, Cicero tells[60] us
that Appius often consulted "soul-oracles" (psychomantia), and also
mentions a man having recourse to one when his son was seriously
ill.[61] The poets have, of course, made free use of this supposed
prophetic power of the dead. The shade of Polydorus, for instance,
speaks the prologue of the Hecuba, while the appearance of the dead
Creusa in the _AEneid_ is known to everyone. In the _Persae_, AEschylus
makes the shade of Darius ignorant of all that has happened since his
death, and is thus able to introduce his famous description of the
battle of Salamis; but Darius, nevertheless, possesses a knowledge of
the future, and can therefore give us an equally vivid account of the
batt