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 100 kilometres (62 mi) south of Smyrna—now İzmir, in Turkey. Herodotus describes it as follows: