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 battle of Plataea, which had not yet taken place. The shade of Clytemnestra in the _Eumenides_, however, does not prophesy. Pliny mentions the belief that the dead had prophetic powers, but declares that they could not always be relied on, as the following instance proves.[62] During the Sicilian war, Gabienus, the bravest man in Caesar's fleet, was captured by Sextus Pompeius, and beheaded by his orders. For a whole day the corpse lay upon the shore, the head almost severed from the body. Then, towards evening, a large crowd assembled, attracted by his groans and prayers; and he begged Sextus Pompeius either to come to him himself or to send some of his friends; for he had returned from the dead, and had something to tell him. Pompeius sent friends, and Gabienus informed them that Pompeius's cause found favour with the gods below, and was the right cause, and that he was bidden to announce that all would end as he wished. To prove the truth of what he said, he announced that he would die immediately, as he actually did.