Apart from Delphi, we know that oracles existed in Dodona, Trophonios,
Claros and Didyma. Homer, Aeschylus, Sophocles and Herodotus mentioned
in their works oracles and the way they functioned. From them we know
that they have played an important role and that the Delphi oracle was
the most famous. Many political leaders asked the oracle’s advice before
taking a decision, which indicated the crucial role it played not only
in ever day life but also in political affairs.
Oracles where established at places that enjoyed a special sanctity
according to ancient Greek beliefs. Elevations, springs, caves and
places struck by lightning are some of the signs, we know, that were
enough to characterize a place sacred. For example the oracle of Dodona
(in Northwest Greece) was established after a lightning (symbol of the
father of gods Dias/Zeus) hit an oak tree (another symbol of Dias/Zeus).