The Panionium (Ancient Greek Πανιώνιον, Paniōnion) was an Ionian sanctuary dedicated to Poseidon Helikonios and the meeting place of the Ionian League. It was on the peninsula of Mt. Mycale, about south of Smyrna—now İzmir, in Turkey. Herodotus defines it as follows:The Panionion's a sacred ground in Mykale, facing north; it was set apart for Poseidon of Helicon by the joint will of the Ionians. Mykale's a western promontory of the mai… (More on Panionium)