The Ionian cities formed a religious and cultural (as opposed to a political or military) confederacy, the Ionian League, of which participation in the Panionic festival was a distinguishing characteristic. This festival took place on the north slope of Mt. Mycale in a shrine called the Panionium. In addition to the Panionic festival at Mycale, which was celebrated mainly by the Asian Ionians, both European and Asian coast Ionians convened on Delos Island each summer to worship at the temple of the Delian Apollo.