This ecstasy was in the case of almost all the oracles of antiquity brought on by inhaling certain gases which rose from the soil and produced often most fearful symptoms in the unfortunate persons employed for the purpose. At the same time they were rarely free from an addition of artifice, as the priests not only filled the mind of the pythoness beforehand with thoughts suggested by their own wisdom and political experience, but the latter also frequently employed her skill as a ventriloquist, in order to increase the force of her revelations. Hence the fact, that almost all the Greek oracles proceeded from deep caves, in which, as at Dodona and Delphi, carbonic gas was developed in abundance; hence, also, the name of _ventriloqua vates_, which was commonly given to the Delphi Pythia. The oldest of these oracles, that at Dodona, foretold events for nearly two thousand years, and even survived the almost universal destruction of such institutions at the time of Christ; it did not actually cease till the third century, when an Illyrian robber cut down the sacred tree. The oracle of Zeus Trophonius in Boeotia spoke through the patients who were brought to the caves, where they became somnambulists, had visions and answered the questions of the priests while they were in this condition. The Romans also had their somnambulist prophets from the earliest days, and whenever the state was in danger, the Sibylline books were consulted. Christianity made an end to all such divination in Italy as in Greece. It is strange that the vast scheme of Egyptian superstition shows us no oracles whatever; but among the Germans prophets were all the more numerous. They foretold war or peace, success or failure, and exercised a powerful influence on all affairs. One of the older prophetesses, Veleda, who lived in an isolated tower, and allowed herself to be but rarely consulted, was held in high esteem even by the Romans. The Celts had in like manner prophet-Druids, some of whom became well known to the Romans, and are reported to have foretold the fate of the emperors Aurelian, Diocletian and Severus.