Cave experiences and ancient Greek oracles

A great number of Greek oracular cults focused on caves, notwithstanding the divergent nature of the divine patrons of these cults. The fundamental reason for locating prophetic activities in caves was the need of the gods' mediums to attain divine inspiration, that is, to alter their state of consciousness. For the purposes of divination the Greeks used at least two methods. The easiest and universally practiced technique was sensory deprivation. Modern research demonstrates that reduction of external stimuli leads to dream-like states, involving release of internal imagery. In the geographic setting of Greece, caverns and grottos provide an easy way to achieve total or near-total isolation. The second technique was based on special geological conditions, namely, a source of poisonous gas having euphoriant or psychotropic effect. The psychotropic or, in the opinion of the Greeks, numinous quality of the caves was common knowledge to such a degree that the association of seers and prophets with caves became universal.