Herodotus describes it as follows:[1]The Panionion is a sacred ground in Mykale, facing north; it was set apart for Poseidon of Helicon by the joint will of the Ionians.
[3] Diodorus writes that the Ionians were forced to move the Panionia from the Panionium to Ephesus, because of war in the surrounding area.
[4] Under Alexander the Great the games and festival were again held at the Panionium, and continued to be so under Roman rule, without however, regaining their previous importance.
In the central area can be seen evidence of a 17.5 by 4.25 m (57.4 by 13.9 ft) rectangular stone, presumed to be the altar of Poseidon, dated from the end of the 6th century BC.
It is 32 m (105 ft) in diameter, a little bit more than semicircular, with 11 rows of seats, cut into solid rock, and is presumed to be the council chamber for the meetings of the Ionian League.
Mycale, discovered another archaeological site high in the mountains, a settlement and an archaic temple (about mid 6th century BC) of the Ionic order.