Dodona was the oldest of the Pagan Greek oracles, located in the mountains of northern Greece, 5 miles SE of the southern most tip of modern Albania and 30 miles inland from the Ionian Sea. There was an Oak grove near a year round stream which dried during the evening and ran during the day. Some claim this was a Beech grove, depending on which of the Tree-month-Gods was being promoted at the time. However, Socrates speaking to Phaedrus (275) says, "There was a tradition in the temple of Dodona that oaks first gave prophetic utterances." Which confirms what Homer says, when he speaks of the, "spelling lofty leaved oak of the God" at Dodona. (Odyssey 14:326-7)
The three Priestesses who kept the shrine and interpreted the Oracle of Zeus, were known as Selli, though in later years, both priest and priestess of Zeus at Dodona were called Selli, or Selloi; and the most ancient name for people of the area was also Selloi.
The priestesses went barefoot, never washed their feet and slept on the bare ground, or as Homer has Achilles say,
"Lord of Dodona, King Zeus, God of Pelasgians, O God who dwells afar, who holds harsh wintery Dodona in your sway, where your interpreters the Selli dwell with feet like roots, unwashed, and make their beds on the ground..." The Iliad 16:127 (authors translation)
These Selli received their Oracle by listening to the clinking of bronze vessels hung in the branches of the trees, the cooing of doves, the sounds of other birds, the rustling of the oak leaves, or the Oak itself when they placed their heads on its heart.
Herodotus (Book II 54-58) has this to say about the origin of the Oracle at Dodona:
"The priests of the Zeus of (Egyptian) Thebes told me that two Priestesses were carried away from that country by Phoenicians, who, as they heard, sold one in Libya and the other in Greece, and these two women established the first oracles in either place. When I asked how they knew this, they said that the Egyptians has searched diligently for these two women, but in vain, and afterward they had learnt what they now told me.
"This account I had from the priests at Thebes; but the prophetesses at Dodona say that two black pigeons flew from Thebes of Egypt, on to Libya an the other to Dodona. The second perched on a beech-tree, and uttered human speech admonishing the people of the place to set up an oracle of Zeus; and they, believing it be a divine revelation, obeyed. They add that the pigeon which flew to Libya commanded the establishment of an oracle of Ammon, also dedicated to Zeus. This is said by the priestesses at Dodona, the oldest of whom is named Promeneia, and the next Timarete, and the youngest Nicandra; and the other servants of the shrine said likewise.
"But my own belief is this. If the Phoenicians did indeed carry off the holy women and sell one in Libya and one in Greece, the part of Greece (called in those days Pelasgia) where they sold the second was Thesprotia. Being kept as a slave there, she consecrated an alter to Zeus under a beech-tree; for we may suppose that she, who had been a priestess of His temple at Thebes would be mindful of His worship in another place. Later she made of it a place of divination, when she had learnt the language of Greece; and she must have said that their sister had been sold in Libya by the same Phoenicians.
"The people of Dodona, I suppose, called these women pigeons because they were foreigners and their speech was no more understood than the chattering of birds; then, when one could speak their language, they reported that the pigeon had spoken with a human voice; for while she spoke a foreign tongue they would think her voice like that of a bird. But how could a pigeon utter the speech of men? And they said the pigeon was black meaning that the woman was an Egyptian.
"Moreover, it is true that the ways of divination at Thebes of Egypt and at Dodona are much alike..."
Historically, Herodotus is close to the truth, but Herodotus knew nothing about spiritual matters, and failed to understand what the Egyptians said. Manetho, the Egyptian historian would later find "great fault with Herodotus for his ignorance and false relations of Egyptian affairs", and Plutarch (On the Malice of Herodotus, 14) accused Herodotus of "using worthless Egyptian stories to overthrow the most solemn and sacred truths of Greek Religion."
However, Herodotus was correct is stating that the original priestess of Dodona was taken from Egypt, [the second to the temple of Ammon in Libya]. This occurred in early Cretan [pre Greek] times, about 500 years before the Trojan War, or about 1750 BCE. This was a time of turmoil not only in Egypt but throughout the mid east. Sumer-Akkad was under attack by Hammurabi and the balance of power in the entire mid east was tilting, just as Taurus, the Bull, which had long been the stable force in the heavens, was giving way to Ares the Ram. It was during this period that the followers of Aries, the Arians (Aryans), invaded northern Akkad and India and the Hyksos invaded Egypt. And so it was that the Egyptian priestess went to desolate and primitive Dodona where she introduced the worship of Isis, Goddess of Magic, and Ra, God of the Sun. The Aryan had not yet formulated their own myth, but rather they borrowed from the peoples they conquered as is evident from the complete lack of continuity of the later Aryan religions. This was the time when Zeus was born on Crete, but Zeus was never a Sun God, and the change of the oracle from that of the Goddess to that of a Greek God reveals just how ancient the oracle at Dodona was. Oracle was given by the Greek God, Apollo, at Delphi and in Greek myth, it was Zeus who sought revelation from Metis and Prometheus. It appears that it was sometime after the fall of Troy, and perhaps even after the Dorian invasion, that Ra would be worshiped under the name of Zeus, and the priestesses of Isis would become the priestesses of Zeus and first augmented then replaced by male priests.
But this was only the latest of the oracles of Dodona, as Dodona had been the seat of oracle for at least a millennium before the Egyptian priestesses arrived. And it is quite likely that the various methods of divination at Dodona were derived from these earlier rites of those Goddesses.